src/nfc/llcp/llcp_dlc.cc

/******************************************************************************
 *
 *  Copyright (C) 2010-2014 Broadcom Corporation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at:
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 ******************************************************************************/

/******************************************************************************
 *
 *  This file contains the LLCP Data Link Connection Management
 *
 ******************************************************************************/

#include <string>

#include <android-base/stringprintf.h>
#include <base/logging.h>

#include "bt_types.h"
#include "gki.h"
#include "llcp_defs.h"
#include "llcp_int.h"
#include "nfc_int.h"

using android::base::StringPrintf;

static tLLCP_STATUS llcp_dlsm_idle(tLLCP_DLCB* p_dlcb, tLLCP_DLC_EVENT event,
                                   void* p_data);
static tLLCP_STATUS llcp_dlsm_w4_remote_resp(tLLCP_DLCB* p_dlcb,
                                             tLLCP_DLC_EVENT event,
                                             void* p_data);
static tLLCP_STATUS llcp_dlsm_w4_local_resp(tLLCP_DLCB* p_dlcb,
                                            tLLCP_DLC_EVENT event,
                                            void* p_data);
static tLLCP_STATUS llcp_dlsm_connected(tLLCP_DLCB* p_dlcb,
                                        tLLCP_DLC_EVENT event, void* p_data);
static tLLCP_STATUS llcp_dlsm_w4_remote_dm(tLLCP_DLCB* p_dlcb,
                                           tLLCP_DLC_EVENT event);
static std::string llcp_dlsm_get_state_name(tLLCP_DLC_STATE state);
static std::string llcp_dlsm_get_event_name(tLLCP_DLC_EVENT event);

extern bool nfc_debug_enabled;
extern unsigned char appl_dta_mode_flag;

/*******************************************************************************
**
** Function         llcp_dlsm_execute
**
** Description      This function executes the state machine for data link
**                  connection.
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
tLLCP_STATUS llcp_dlsm_execute(tLLCP_DLCB* p_dlcb, tLLCP_DLC_EVENT event,
                               void* p_data) {
  tLLCP_STATUS status;

  DLOG_IF(INFO, nfc_debug_enabled)
      << StringPrintf("DLC (0x%02X) - state: %s, evt: %s", p_dlcb->local_sap,
                      llcp_dlsm_get_state_name(p_dlcb->state).c_str(),
                      llcp_dlsm_get_event_name(event).c_str());

  switch (p_dlcb->state) {
    case LLCP_DLC_STATE_IDLE:
      status = llcp_dlsm_idle(p_dlcb, event, p_data);
      break;

    case LLCP_DLC_STATE_W4_REMOTE_RESP:
      status = llcp_dlsm_w4_remote_resp(p_dlcb, event, p_data);
      break;

    case LLCP_DLC_STATE_W4_LOCAL_RESP:
      status = llcp_dlsm_w4_local_resp(p_dlcb, event, p_data);
      break;

    case LLCP_DLC_STATE_CONNECTED:
      status = llcp_dlsm_connected(p_dlcb, event, p_data);
      break;

    case LLCP_DLC_STATE_W4_REMOTE_DM:
      status = llcp_dlsm_w4_remote_dm(p_dlcb, event);
      break;

    default:
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlsm_idle
**
** Description      Data link connection is in idle state
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
static tLLCP_STATUS llcp_dlsm_idle(tLLCP_DLCB* p_dlcb, tLLCP_DLC_EVENT event,
                                   void* p_data) {
  tLLCP_STATUS status = LLCP_STATUS_SUCCESS;
  tLLCP_SAP_CBACK_DATA data;
  tLLCP_CONNECTION_PARAMS* p_params;

  switch (event) {
    case LLCP_DLC_EVENT_API_CONNECT_REQ:

      /* upper layer requests to create data link connection */
      p_params = (tLLCP_CONNECTION_PARAMS*)p_data;

      status = llcp_util_send_connect(p_dlcb, p_params);

      if (status == LLCP_STATUS_SUCCESS) {
        p_dlcb->local_miu = p_params->miu;
        p_dlcb->local_rw = p_params->rw;

        /* wait for response from peer device */
        p_dlcb->state = LLCP_DLC_STATE_W4_REMOTE_RESP;

        nfc_start_quick_timer(&p_dlcb->timer, NFC_TTYPE_LLCP_DATA_LINK,
                              (uint32_t)(llcp_cb.lcb.data_link_timeout *
                                         QUICK_TIMER_TICKS_PER_SEC) /
                                  1000);
      }
      break;

    case LLCP_DLC_EVENT_PEER_CONNECT_IND:

      /* peer device requests to create data link connection */
      p_params = (tLLCP_CONNECTION_PARAMS*)p_data;

      if (p_params->miu > llcp_cb.lcb.peer_miu) {
        LOG(WARNING) << StringPrintf(
            "Peer sent data link MIU bigger than peer's "
            "link MIU");
        p_params->miu = llcp_cb.lcb.peer_miu;
      }

      data.connect_ind.event = LLCP_SAP_EVT_CONNECT_IND;
      data.connect_ind.remote_sap = p_dlcb->remote_sap;
      data.connect_ind.local_sap = p_dlcb->local_sap;
      data.connect_ind.miu = p_params->miu;
      data.connect_ind.rw = p_params->rw;
      data.connect_ind.p_service_name = p_params->sn;
      data.connect_ind.server_sap = p_dlcb->local_sap;

      p_dlcb->remote_miu = p_params->miu;
      p_dlcb->remote_rw = p_params->rw;

      DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
          "Remote MIU:%d, RW:%d", p_dlcb->remote_miu, p_dlcb->remote_rw);

      /* wait for response from upper layer */
      p_dlcb->state = LLCP_DLC_STATE_W4_LOCAL_RESP;

      nfc_start_quick_timer(&p_dlcb->timer, NFC_TTYPE_LLCP_DATA_LINK,
                            (uint32_t)(llcp_cb.lcb.data_link_timeout *
                                       QUICK_TIMER_TICKS_PER_SEC) /
                                1000);

      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected event");
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlsm_w4_remote_resp
**
** Description      data link connection is waiting for connection confirm from
**                  peer
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
static tLLCP_STATUS llcp_dlsm_w4_remote_resp(tLLCP_DLCB* p_dlcb,
                                             tLLCP_DLC_EVENT event,
                                             void* p_data) {
  tLLCP_STATUS status = LLCP_STATUS_SUCCESS;
  tLLCP_SAP_CBACK_DATA data;
  tLLCP_CONNECTION_PARAMS* p_params;

  switch (event) {
    case LLCP_DLC_EVENT_PEER_CONNECT_CFM:

      /* peer device accepted data link connection */
      nfc_stop_quick_timer(&p_dlcb->timer);

      p_params = (tLLCP_CONNECTION_PARAMS*)p_data;

      /* data link MIU must be up to link MIU */
      if (p_params->miu > llcp_cb.lcb.peer_miu) {
        LOG(WARNING) << StringPrintf(
            "Peer sent data link MIU bigger than "
            "peer's link MIU");
        p_params->miu = llcp_cb.lcb.peer_miu;
      }

      p_dlcb->remote_miu = p_params->miu;
      p_dlcb->remote_rw = p_params->rw;

      DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
          "Remote MIU:%d, RW:%d", p_dlcb->remote_miu, p_dlcb->remote_rw);

      p_dlcb->state = LLCP_DLC_STATE_CONNECTED;
      llcp_util_adjust_dl_rx_congestion();

      data.connect_resp.event = LLCP_SAP_EVT_CONNECT_RESP;
      data.connect_resp.remote_sap = p_dlcb->remote_sap;
      data.connect_resp.local_sap = p_dlcb->local_sap;
      data.connect_resp.miu = p_params->miu;
      data.connect_resp.rw = p_params->rw;

      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      if (llcp_cb.overall_rx_congested) {
        p_dlcb->flags |= LLCP_DATA_LINK_FLAG_PENDING_RR_RNR;
      }
      break;

    case LLCP_DLC_EVENT_PEER_DISCONNECT_RESP:
    case LLCP_DLC_EVENT_TIMEOUT:

      /* peer device rejected connection or didn't respond */
      data.disconnect_resp.event = LLCP_SAP_EVT_DISCONNECT_RESP;
      data.disconnect_resp.local_sap = p_dlcb->local_sap;
      data.disconnect_resp.remote_sap = p_dlcb->remote_sap;
      data.disconnect_resp.reason = *((uint8_t*)p_data);
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      /* stop timer, flush any pending data in queue and deallocate control
       * block */
      llcp_util_deallocate_data_link(p_dlcb);

      llcp_util_adjust_dl_rx_congestion();
      break;

    case LLCP_DLC_EVENT_FRAME_ERROR:
    case LLCP_DLC_EVENT_LINK_ERROR:

      /* received bad frame or link is deactivated */
      data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
      data.disconnect_ind.local_sap = p_dlcb->local_sap;
      data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected event");
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlsm_w4_local_resp
**
** Description      data link connection is waiting for connection confirm from
**                  application
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
static tLLCP_STATUS llcp_dlsm_w4_local_resp(tLLCP_DLCB* p_dlcb,
                                            tLLCP_DLC_EVENT event,
                                            void* p_data) {
  tLLCP_STATUS status = LLCP_STATUS_SUCCESS;
  tLLCP_CONNECTION_PARAMS* p_params;
  tLLCP_SAP_CBACK_DATA data;
  uint8_t reason;

  switch (event) {
    case LLCP_DLC_EVENT_API_CONNECT_CFM:

      /* upper layer accepted data link connection */
      nfc_stop_quick_timer(&p_dlcb->timer);

      p_params = (tLLCP_CONNECTION_PARAMS*)p_data;

      p_dlcb->local_miu = p_params->miu;
      p_dlcb->local_rw = p_params->rw;

      p_dlcb->state = LLCP_DLC_STATE_CONNECTED;

      if (llcp_cb.overall_rx_congested) {
        p_dlcb->flags |= LLCP_DATA_LINK_FLAG_PENDING_RR_RNR;
      }

      status = llcp_util_send_cc(p_dlcb, p_params);

      if (status == LLCP_STATUS_SUCCESS) {
        llcp_util_adjust_dl_rx_congestion();
      } else {
        data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
        data.disconnect_ind.local_sap = p_dlcb->local_sap;
        data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
        (*p_dlcb->p_app_cb->p_app_cback)(&data);

        llcp_util_deallocate_data_link(p_dlcb);
      }
      break;

    case LLCP_DLC_EVENT_API_CONNECT_REJECT:
    case LLCP_DLC_EVENT_TIMEOUT:

      if (event == LLCP_DLC_EVENT_TIMEOUT)
        reason = LLCP_SAP_DM_REASON_TEMP_REJECT_THIS;
      else
        reason = *((uint8_t*)p_data);

      /* upper layer rejected connection or didn't respond */
      llcp_util_send_dm(p_dlcb->remote_sap, p_dlcb->local_sap, reason);

      /* stop timer, flush any pending data in queue and deallocate control
       * block */
      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    case LLCP_DLC_EVENT_FRAME_ERROR:
    case LLCP_DLC_EVENT_LINK_ERROR:

      /* received bad frame or link is deactivated */
      data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
      data.disconnect_ind.local_sap = p_dlcb->local_sap;
      data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected event");
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlsm_connected
**
** Description      data link connection is connected
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
static tLLCP_STATUS llcp_dlsm_connected(tLLCP_DLCB* p_dlcb,
                                        tLLCP_DLC_EVENT event, void* p_data) {
  bool flush;
  tLLCP_STATUS status = LLCP_STATUS_SUCCESS;
  tLLCP_SAP_CBACK_DATA data;

  switch (event) {
    case LLCP_DLC_EVENT_API_DISCONNECT_REQ:

      /* upper layer requests to disconnect */
      flush = *(bool*)(p_data);

      /*
      ** if upper layer asks to discard any pending data
      ** or there is no pending data/ack to send and it is not waiting for ack
      */
      if ((flush) || ((p_dlcb->i_xmit_q.count == 0) &&
                      (p_dlcb->next_rx_seq == p_dlcb->sent_ack_seq) &&
                      (p_dlcb->next_tx_seq == p_dlcb->rcvd_ack_seq))) {
        /* wait for disconnect response */
        p_dlcb->state = LLCP_DLC_STATE_W4_REMOTE_DM;

        llcp_util_send_disc(p_dlcb->remote_sap, p_dlcb->local_sap);

        nfc_start_quick_timer(&p_dlcb->timer, NFC_TTYPE_LLCP_DATA_LINK,
                              (uint32_t)(llcp_cb.lcb.data_link_timeout *
                                         QUICK_TIMER_TICKS_PER_SEC) /
                                  1000);
      } else {
        /* set flag to send DISC when tx queue is empty */
        p_dlcb->flags |= LLCP_DATA_LINK_FLAG_PENDING_DISC;
      }
      break;

    case LLCP_DLC_EVENT_PEER_DISCONNECT_IND:

      /* peer device requests to disconnect */

      /* send disconnect response and notify upper layer */
      llcp_util_send_dm(p_dlcb->remote_sap, p_dlcb->local_sap,
                        LLCP_SAP_DM_REASON_RESP_DISC);

      data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
      data.disconnect_ind.local_sap = p_dlcb->local_sap;
      data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    case LLCP_DLC_EVENT_API_DATA_REQ:

      /* upper layer requests to send data */

      /* if peer device can receive data */
      if (p_dlcb->remote_rw) {
        /* enqueue data and check if data can be sent */
        GKI_enqueue(&p_dlcb->i_xmit_q, p_data);
        llcp_cb.total_tx_i_pdu++;

        llcp_link_check_send_data();

        if ((p_dlcb->is_tx_congested) || (llcp_cb.overall_tx_congested) ||
            (p_dlcb->remote_busy) ||
            (p_dlcb->i_xmit_q.count >=
             p_dlcb->remote_rw)) /*if enough data to send next round */
        {
          DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
              "Data link (SSAP:DSAP=0x%X:0x%X) "
              "congested: xmit_q.count=%d",
              p_dlcb->local_sap, p_dlcb->remote_sap, p_dlcb->i_xmit_q.count);

          /* set congested here so overall congestion check routine will not
           * report event again */
          p_dlcb->is_tx_congested = true;
          status = LLCP_STATUS_CONGESTED;
        }
      } else {
        LOG(ERROR) << StringPrintf("Remote RW is zero: discard data");
        /* buffer will be freed when returned to API function */
        status = LLCP_STATUS_FAIL;
      }
      break;

    case LLCP_DLC_EVENT_PEER_DATA_IND:
      /* peer device sends data so notify upper layer to read data from data
       * link connection */

      data.data_ind.event = LLCP_SAP_EVT_DATA_IND;
      data.data_ind.local_sap = p_dlcb->local_sap;
      data.data_ind.link_type = LLCP_LINK_TYPE_DATA_LINK_CONNECTION;
      data.data_ind.remote_sap = p_dlcb->remote_sap;

      (*p_dlcb->p_app_cb->p_app_cback)(&data);
      break;

    case LLCP_DLC_EVENT_FRAME_ERROR:
    case LLCP_DLC_EVENT_LINK_ERROR:

      /* received bad frame or link is deactivated */
      data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
      data.disconnect_ind.local_sap = p_dlcb->local_sap;
      data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected event");
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlsm_w4_remote_dm
**
** Description      data link connection is waiting for disconnection confirm
**                  from peer
**
** Returns          tLLCP_STATUS
**
*******************************************************************************/
static tLLCP_STATUS llcp_dlsm_w4_remote_dm(tLLCP_DLCB* p_dlcb,
                                           tLLCP_DLC_EVENT event) {
  tLLCP_STATUS status = LLCP_STATUS_SUCCESS;
  tLLCP_SAP_CBACK_DATA data;

  switch (event) {
    case LLCP_DLC_EVENT_PEER_DISCONNECT_RESP:
    case LLCP_DLC_EVENT_TIMEOUT:

      /* peer device sends disconnect response or didn't responde */
      data.disconnect_resp.event = LLCP_SAP_EVT_DISCONNECT_RESP;
      data.disconnect_resp.local_sap = p_dlcb->local_sap;
      data.disconnect_resp.remote_sap = p_dlcb->remote_sap;
      data.disconnect_resp.reason = LLCP_SAP_DM_REASON_RESP_DISC;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    case LLCP_DLC_EVENT_FRAME_ERROR:
    case LLCP_DLC_EVENT_LINK_ERROR:

      /* received bad frame or link is deactivated */
      data.disconnect_ind.event = LLCP_SAP_EVT_DISCONNECT_IND;
      data.disconnect_ind.local_sap = p_dlcb->local_sap;
      data.disconnect_ind.remote_sap = p_dlcb->remote_sap;
      (*p_dlcb->p_app_cb->p_app_cback)(&data);

      llcp_util_deallocate_data_link(p_dlcb);
      llcp_util_adjust_dl_rx_congestion();
      break;

    case LLCP_DLC_EVENT_PEER_DATA_IND:
      break;

    case LLCP_DLC_EVENT_PEER_DISCONNECT_IND:
      /* it's race condition, send disconnect response and wait for DM */
      llcp_util_send_dm(p_dlcb->remote_sap, p_dlcb->local_sap,
                        LLCP_SAP_DM_REASON_RESP_DISC);
      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected event");
      status = LLCP_STATUS_FAIL;
      break;
  }

  return status;
}

/*******************************************************************************
**
** Function         llcp_dlc_find_dlcb_by_local_sap
**
** Description      Find tLLCP_DLCB by local SAP and remote SAP
**                  if remote_sap is LLCP_INVALID_SAP, it will return a DLCB
**                  which is waiting for CC from peer.
**
** Returns          tLLCP_DLCB *
**
*******************************************************************************/
tLLCP_DLCB* llcp_dlc_find_dlcb_by_sap(uint8_t local_sap, uint8_t remote_sap) {
  int i;

  for (i = 0; i < LLCP_MAX_DATA_LINK; i++) {
    if ((llcp_cb.dlcb[i].state != LLCP_DLC_STATE_IDLE) &&
        (llcp_cb.dlcb[i].local_sap == local_sap)) {
      if ((remote_sap == LLCP_INVALID_SAP) &&
          (llcp_cb.dlcb[i].state == LLCP_DLC_STATE_W4_REMOTE_RESP)) {
        /* Remote SAP has not been finalized because we are watiing for CC */
        return (&llcp_cb.dlcb[i]);
      } else if (llcp_cb.dlcb[i].remote_sap == remote_sap) {
        return (&llcp_cb.dlcb[i]);
      }
    }
  }
  return NULL;
}

/*******************************************************************************
**
** Function         llcp_dlc_flush_q
**
** Description      Free buffers in tx and rx queue in data link
**
** Returns          void
**
*******************************************************************************/
void llcp_dlc_flush_q(tLLCP_DLCB* p_dlcb) {
  if (p_dlcb) {
    DLOG_IF(INFO, nfc_debug_enabled)
        << StringPrintf("local SAP:0x%02X", p_dlcb->local_sap);

    /* Release any held buffers */
    while (p_dlcb->i_xmit_q.p_first) {
      GKI_freebuf(GKI_dequeue(&p_dlcb->i_xmit_q));
      llcp_cb.total_tx_i_pdu--;
    }

    /* discard any received I PDU on data link  including in AGF */
    LLCP_FlushDataLinkRxData(p_dlcb->local_sap, p_dlcb->remote_sap);
  } else {
    LOG(ERROR) << StringPrintf("p_dlcb is NULL");
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_connect_pdu
**
** Description      Process CONNECT PDU
**
** Returns          void
**
*******************************************************************************/
static void llcp_dlc_proc_connect_pdu(uint8_t dsap, uint8_t ssap,
                                      uint16_t length, uint8_t* p_data) {
  tLLCP_DLCB* p_dlcb;
  tLLCP_STATUS status;
  tLLCP_APP_CB* p_app_cb;

  tLLCP_CONNECTION_PARAMS params;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  p_app_cb = llcp_util_get_app_cb(dsap);

  if ((p_app_cb == NULL) || (p_app_cb->p_app_cback == NULL) ||
      ((p_app_cb->link_type & LLCP_LINK_TYPE_DATA_LINK_CONNECTION) == 0)) {
    LOG(ERROR) << StringPrintf("Unregistered SAP:0x%x", dsap);
    llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_NO_SERVICE);
    return;
  }

  /* parse CONNECT PDU and get connection parameters */
  if (llcp_util_parse_connect(p_data, length, &params) != LLCP_STATUS_SUCCESS) {
    LOG(ERROR) << StringPrintf("Bad format CONNECT");
    /* fix to pass TC_CTO_TAR_BI_02_x (x=5) test case
     * As per the LLCP test specification v1.2.00 by receiving erroneous SNL PDU
     * i'e with improper length and service name "urn:nfc:sn:dta-co-echo-in",
     * the IUT should not send any PDU except SYMM PDU */

    if (appl_dta_mode_flag == 1 &&
        p_data[1] == strlen((const char*)&p_data[2])) {
      DLOG_IF(INFO, nfc_debug_enabled)
          << StringPrintf("%s: Strings are not equal", __func__);
      llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_NO_SERVICE);
    } else {
      llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_NO_SERVICE);
    }
    return;
  }

  /* if this is connection by service name */
  if (dsap == LLCP_SAP_SDP) {
    /* find registered SAP with service name */
    if (strlen(params.sn))
      dsap = llcp_sdp_get_sap_by_name(params.sn, (uint8_t)strlen(params.sn));
    else {
      /* if SN type is included without SN */
      if (params.sn[1] == LLCP_SN_TYPE) {
        llcp_util_send_dm(ssap, LLCP_SAP_SDP, LLCP_SAP_DM_REASON_NO_SERVICE);
      } else {
        /* SDP doesn't accept connection */
        llcp_util_send_dm(ssap, LLCP_SAP_SDP,
                          LLCP_SAP_DM_REASON_PERM_REJECT_THIS);
      }
      return;
    }

    if (dsap == LLCP_SAP_SDP) {
      LOG(ERROR) << StringPrintf("SDP doesn't accept connection");

      llcp_util_send_dm(ssap, LLCP_SAP_SDP,
                        LLCP_SAP_DM_REASON_PERM_REJECT_THIS);
      return;
    } else if (dsap == 0) {
      LOG(ERROR) << StringPrintf("Unregistered Service:%s", params.sn);

      llcp_util_send_dm(ssap, LLCP_SAP_SDP, LLCP_SAP_DM_REASON_NO_SERVICE);
      return;
    } else {
      /* check if this application can support connection-oriented transport */
      p_app_cb = llcp_util_get_app_cb(dsap);

      if ((p_app_cb == NULL) || (p_app_cb->p_app_cback == NULL) ||
          ((p_app_cb->link_type & LLCP_LINK_TYPE_DATA_LINK_CONNECTION) == 0)) {
        LOG(ERROR) << StringPrintf(
            "SAP(0x%x) doesn't support "
            "connection-oriented",
            dsap);
        llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_NO_SERVICE);
        return;
      }
    }
  }

  /* check if any data link */
  p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
  if (p_dlcb) {
    LOG(ERROR) << StringPrintf("Data link is aleady established");
    llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_TEMP_REJECT_THIS);
  } else {
    /* allocate data link connection control block and notify upper layer
     * through state machine */
    p_dlcb = llcp_util_allocate_data_link(dsap, ssap);

    if (p_dlcb) {
      status =
          llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_PEER_CONNECT_IND, &params);
      if (status != LLCP_STATUS_SUCCESS) {
        LOG(ERROR) << StringPrintf("Error in state machine");
        llcp_util_deallocate_data_link(p_dlcb);
      }
    } else {
      LOG(ERROR) << StringPrintf("Out of resource");
      llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_TEMP_REJECT_ANY);
    }
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_disc_pdu
**
** Description      Process DISC PDU
**
** Returns          void
**
*******************************************************************************/
static void llcp_dlc_proc_disc_pdu(uint8_t dsap, uint8_t ssap,
                                   uint16_t length) {
  tLLCP_DLCB* p_dlcb;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
  if (p_dlcb) {
    if (length > 0) {
      LOG(ERROR) << StringPrintf(
          "Received extra data (%d bytes) in DISC "
          "PDU",
          length);

      llcp_util_send_frmr(p_dlcb,
                          LLCP_FRMR_W_ERROR_FLAG | LLCP_FRMR_I_ERROR_FLAG,
                          LLCP_PDU_DISC_TYPE, 0);
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
    } else {
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_PEER_DISCONNECT_IND, NULL);
    }
  } else {
    LOG(ERROR) << StringPrintf("No data link for SAP (0x%x,0x%x)", dsap, ssap);
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_cc_pdu
**
** Description      Process CC PDU
**
** Returns          void
**
*******************************************************************************/
static void llcp_dlc_proc_cc_pdu(uint8_t dsap, uint8_t ssap, uint16_t length,
                                 uint8_t* p_data) {
  tLLCP_DLCB* p_dlcb;
  tLLCP_CONNECTION_PARAMS params;
  tLLCP_STATUS status;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  /* find a DLCB waiting for CC on this local SAP */
  p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, LLCP_INVALID_SAP);
  if (p_dlcb) {
    /* The CC may contain a SSAP that is different from the DSAP in the CONNECT
     */
    p_dlcb->remote_sap = ssap;

    if (llcp_util_parse_cc(p_data, length, &(params.miu), &(params.rw)) ==
        LLCP_STATUS_SUCCESS) {
      status =
          llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_PEER_CONNECT_CFM, &params);
      if (status != LLCP_STATUS_SUCCESS) {
        LOG(ERROR) << StringPrintf("Error in state machine");
        llcp_util_deallocate_data_link(p_dlcb);
      }
    } else {
      llcp_util_send_frmr(p_dlcb,
                          LLCP_FRMR_W_ERROR_FLAG | LLCP_FRMR_I_ERROR_FLAG,
                          LLCP_PDU_DISC_TYPE, 0);
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
    }
  } else {
    LOG(ERROR) << StringPrintf("No data link for SAP (0x%x,0x%x)", dsap, ssap);
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_dm_pdu
**
** Description      Process DM PDU
**
** Returns          void
**
*******************************************************************************/
static void llcp_dlc_proc_dm_pdu(uint8_t dsap, uint8_t ssap, uint16_t length,
                                 uint8_t* p_data) {
  tLLCP_DLCB* p_dlcb;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  if (length != LLCP_PDU_DM_SIZE - LLCP_PDU_HEADER_SIZE) {
    LOG(ERROR) << StringPrintf("Received invalid DM PDU");
  } else {
    if (*p_data == LLCP_SAP_DM_REASON_RESP_DISC) {
      /* local device initiated disconnecting */
      p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
    } else {
      /* peer device rejected connection with any reason */
      /* find a DLCB waiting for CC on this local SAP    */
      p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, LLCP_INVALID_SAP);
    }

    if (p_dlcb) {
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_PEER_DISCONNECT_RESP,
                        p_data); /* passing reason */
    } else {
      LOG(ERROR) << StringPrintf("No data link for SAP (0x%x,0x%x)", dsap,
                                 ssap);
    }
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_i_pdu
**
** Description      Process I PDU
**
** Returns          void
**
*******************************************************************************/
void llcp_dlc_proc_i_pdu(uint8_t dsap, uint8_t ssap, uint16_t i_pdu_length,
                         uint8_t* p_i_pdu, NFC_HDR* p_msg) {
  uint8_t *p, *p_dst, send_seq, rcv_seq, error_flags;
  uint16_t info_len, available_bytes;
  tLLCP_DLCB* p_dlcb;
  bool appended;
  NFC_HDR* p_last_buf;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);

  if ((p_dlcb) && (p_dlcb->state == LLCP_DLC_STATE_CONNECTED)) {
    error_flags = 0;

    if (p_msg) {
      i_pdu_length = p_msg->len;
      p_i_pdu = (uint8_t*)(p_msg + 1) + p_msg->offset;
    }

    info_len = i_pdu_length - LLCP_PDU_HEADER_SIZE - LLCP_SEQUENCE_SIZE;

    if (info_len > p_dlcb->local_miu) {
      LOG(ERROR) << StringPrintf(
          "exceeding local MIU (%d bytes): got %d "
          "bytes SDU",
          p_dlcb->local_miu, info_len);

      error_flags |= LLCP_FRMR_I_ERROR_FLAG;
    }

    /* get sequence numbers */
    p = p_i_pdu + LLCP_PDU_HEADER_SIZE;

    send_seq = LLCP_GET_NS(*p);
    rcv_seq = LLCP_GET_NR(*p);

    DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
        "LLCP RX I PDU - N(S,R):(%d,%d) V(S,SA,R,RA):(%d,%d,%d,%d)", send_seq,
        rcv_seq, p_dlcb->next_tx_seq, p_dlcb->rcvd_ack_seq, p_dlcb->next_rx_seq,
        p_dlcb->sent_ack_seq);

    /* if send sequence number, N(S) is not expected one, V(R) */
    if (p_dlcb->next_rx_seq != send_seq) {
      LOG(ERROR) << StringPrintf("Bad N(S) got:%d, expected:%d", send_seq,
                                 p_dlcb->next_rx_seq);

      error_flags |= LLCP_FRMR_S_ERROR_FLAG;
    } else {
      /* if peer device sends more than our receiving window size */
      if ((uint8_t)(send_seq - p_dlcb->sent_ack_seq) % LLCP_SEQ_MODULO >=
          p_dlcb->local_rw) {
        LOG(ERROR) << StringPrintf("Bad N(S):%d >= V(RA):%d + RW(L):%d",
                                   send_seq, p_dlcb->sent_ack_seq,
                                   p_dlcb->local_rw);

        error_flags |= LLCP_FRMR_S_ERROR_FLAG;
      }
    }

    /* check N(R) is in valid range; V(SA) <= N(R) <= V(S) */
    if ((uint8_t)(rcv_seq - p_dlcb->rcvd_ack_seq) % LLCP_SEQ_MODULO +
            (uint8_t)(p_dlcb->next_tx_seq - rcv_seq) % LLCP_SEQ_MODULO !=
        (uint8_t)(p_dlcb->next_tx_seq - p_dlcb->rcvd_ack_seq) %
            LLCP_SEQ_MODULO) {
      error_flags |= LLCP_FRMR_R_ERROR_FLAG;
      LOG(ERROR) << StringPrintf("Bad N(R):%d valid range [V(SA):%d, V(S):%d]",
                                 rcv_seq, p_dlcb->rcvd_ack_seq,
                                 p_dlcb->next_tx_seq);
    }

    /* if any error is found */
    if (error_flags) {
      llcp_util_send_frmr(p_dlcb, error_flags, LLCP_PDU_I_TYPE, *p);
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
    } else {
      /* update local sequence variables */
      p_dlcb->next_rx_seq = (p_dlcb->next_rx_seq + 1) % LLCP_SEQ_MODULO;
      p_dlcb->rcvd_ack_seq = rcv_seq;

      appended = false;

      /* get last buffer in rx queue */
      p_last_buf = (NFC_HDR*)GKI_getlast(&p_dlcb->i_rx_q);

      if (p_last_buf) {
        /* get max length to append at the end of buffer */
        available_bytes = GKI_get_buf_size(p_last_buf) - NFC_HDR_SIZE -
                          p_last_buf->offset - p_last_buf->len;

        /* if new UI PDU with length can be attached at the end of buffer */
        if (available_bytes >= LLCP_PDU_AGF_LEN_SIZE + info_len) {
          p_dst =
              (uint8_t*)(p_last_buf + 1) + p_last_buf->offset + p_last_buf->len;

          /* add length of information in I PDU */
          UINT16_TO_BE_STREAM(p_dst, info_len);

          /* copy information of I PDU */
          p = p_i_pdu + LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE;

          memcpy(p_dst, p, info_len);

          p_last_buf->len += LLCP_PDU_AGF_LEN_SIZE + info_len;

          if (p_msg) {
            GKI_freebuf(p_msg);
            p_msg = NULL;
          }

          appended = true;
        }
      }

      /* if it is not available to append */
      if (!appended) {
        /* if it's not from AGF PDU */
        if (p_msg) {
          /* add length of information in front of information */
          p = p_i_pdu + LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE -
              LLCP_PDU_AGF_LEN_SIZE;
          UINT16_TO_BE_STREAM(p, info_len);

          p_msg->offset +=
              LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE - LLCP_PDU_AGF_LEN_SIZE;
          p_msg->len -=
              LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE - LLCP_PDU_AGF_LEN_SIZE;
          p_msg->layer_specific = 0;
        } else {
          p_msg = (NFC_HDR*)GKI_getpoolbuf(LLCP_POOL_ID);

          if (p_msg) {
            p_dst = (uint8_t*)(p_msg + 1);

            /* add length of information in front of information */
            UINT16_TO_BE_STREAM(p_dst, info_len);

            p = p_i_pdu + LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE;
            memcpy(p_dst, p, info_len);

            p_msg->offset = 0;
            p_msg->len = LLCP_PDU_AGF_LEN_SIZE + info_len;
            p_msg->layer_specific = 0;
          } else {
            LOG(ERROR) << StringPrintf("out of buffer");
          }
        }

        /* insert I PDU in rx queue */
        if (p_msg) {
          GKI_enqueue(&p_dlcb->i_rx_q, p_msg);
          p_msg = NULL;
          llcp_cb.total_rx_i_pdu++;

          llcp_util_check_rx_congested_status();
        }
      }

      p_dlcb->num_rx_i_pdu++;

      if ((!p_dlcb->local_busy) && (p_dlcb->num_rx_i_pdu == 1)) {
        /* notify rx data is available so upper layer reads data until queue is
         * empty */
        llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_PEER_DATA_IND, NULL);
      }

      if ((!p_dlcb->is_rx_congested) &&
          (p_dlcb->num_rx_i_pdu >= p_dlcb->rx_congest_threshold)) {
        DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
            "congested num_rx_i_pdu=%d, "
            "rx_congest_threshold=%d",
            p_dlcb->num_rx_i_pdu, p_dlcb->rx_congest_threshold);

        /* send RNR */
        p_dlcb->is_rx_congested = true;
        p_dlcb->flags |= LLCP_DATA_LINK_FLAG_PENDING_RR_RNR;
      }
    }
  } else {
    LOG(ERROR) << StringPrintf("No data link for SAP (0x%x,0x%x)", dsap, ssap);
    llcp_util_send_dm(ssap, dsap, LLCP_SAP_DM_REASON_NO_ACTIVE_CONNECTION);
  }

  if (p_msg) {
    GKI_freebuf(p_msg);
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_rr_rnr_pdu
**
** Description      Process RR or RNR PDU
**
** Returns          void
**
*******************************************************************************/
static void llcp_dlc_proc_rr_rnr_pdu(uint8_t dsap, uint8_t ptype, uint8_t ssap,
                                     uint16_t length, uint8_t* p_data) {
  uint8_t rcv_seq, error_flags;
  tLLCP_DLCB* p_dlcb;
  bool flush = true;
  tLLCP_SAP_CBACK_DATA cback_data;
  bool old_remote_busy;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
  if (p_dlcb != NULL) {
    error_flags = 0;

    rcv_seq = LLCP_GET_NR(*p_data);

    if (length != LLCP_PDU_RR_SIZE - LLCP_PDU_HEADER_SIZE) {
      error_flags |= LLCP_FRMR_W_ERROR_FLAG | LLCP_FRMR_I_ERROR_FLAG;
    }

    /* check N(R) is in valid range; V(SA) <= N(R) <= V(S) */
    if ((uint8_t)(rcv_seq - p_dlcb->rcvd_ack_seq) % LLCP_SEQ_MODULO +
            (uint8_t)(p_dlcb->next_tx_seq - rcv_seq) % LLCP_SEQ_MODULO !=
        (uint8_t)(p_dlcb->next_tx_seq - p_dlcb->rcvd_ack_seq) %
            LLCP_SEQ_MODULO) {
      error_flags |= LLCP_FRMR_R_ERROR_FLAG;
      LOG(ERROR) << StringPrintf(
          "Bad N(R):%d valid range [V(SA):%d, "
          "V(S):%d]",
          rcv_seq, p_dlcb->rcvd_ack_seq, p_dlcb->next_tx_seq);
    }

    if (error_flags) {
      llcp_util_send_frmr(p_dlcb, error_flags, ptype, *p_data);
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
    } else {
      p_dlcb->rcvd_ack_seq = rcv_seq;

      DLOG_IF(INFO, nfc_debug_enabled)
          << StringPrintf("LLCP RX - N(S,R):(NA,%d) V(S,SA,R,RA):(%d,%d,%d,%d)",
                          rcv_seq, p_dlcb->next_tx_seq, p_dlcb->rcvd_ack_seq,
                          p_dlcb->next_rx_seq, p_dlcb->sent_ack_seq);
      old_remote_busy = p_dlcb->remote_busy;
      if (ptype == LLCP_PDU_RNR_TYPE) {
        p_dlcb->remote_busy = true;
        /* if upper layer hasn't get congestion started notification */
        if ((!old_remote_busy) && (!p_dlcb->is_tx_congested)) {
          LOG(WARNING) << StringPrintf(
              "Data link (SSAP:DSAP=0x%X:0x%X) "
              "congestion start: i_xmit_q.count=%d",
              p_dlcb->local_sap, p_dlcb->remote_sap, p_dlcb->i_xmit_q.count);

          cback_data.congest.event = LLCP_SAP_EVT_CONGEST;
          cback_data.congest.local_sap = p_dlcb->local_sap;
          cback_data.congest.remote_sap = p_dlcb->remote_sap;
          cback_data.congest.is_congested = true;
          cback_data.congest.link_type = LLCP_LINK_TYPE_DATA_LINK_CONNECTION;

          (*p_dlcb->p_app_cb->p_app_cback)(&cback_data);
        }
      } else {
        p_dlcb->remote_busy = false;
        /* if upper layer hasn't get congestion ended notification and data link
         * is not congested */
        if ((old_remote_busy) && (!p_dlcb->is_tx_congested)) {
          LOG(WARNING) << StringPrintf(
              "Data link (SSAP:DSAP=0x%X:0x%X) "
              "congestion end: i_xmit_q.count=%d",
              p_dlcb->local_sap, p_dlcb->remote_sap, p_dlcb->i_xmit_q.count);

          cback_data.congest.event = LLCP_SAP_EVT_CONGEST;
          cback_data.congest.local_sap = p_dlcb->local_sap;
          cback_data.congest.remote_sap = p_dlcb->remote_sap;
          cback_data.congest.is_congested = false;
          cback_data.congest.link_type = LLCP_LINK_TYPE_DATA_LINK_CONNECTION;

          (*p_dlcb->p_app_cb->p_app_cback)(&cback_data);
        }
      }

      /* check flag to send DISC when tx queue is empty */
      if (p_dlcb->flags & LLCP_DATA_LINK_FLAG_PENDING_DISC) {
        /* if no pending data and all PDU is acked */
        if ((p_dlcb->i_xmit_q.count == 0) &&
            (p_dlcb->next_rx_seq == p_dlcb->sent_ack_seq) &&
            (p_dlcb->next_tx_seq == p_dlcb->rcvd_ack_seq)) {
          p_dlcb->flags &= ~LLCP_DATA_LINK_FLAG_PENDING_DISC;
          llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_API_DISCONNECT_REQ, &flush);
        }
      }
    }
  } else {
    LOG(ERROR) << StringPrintf("No data link for SAP (0x%x,0x%x)", dsap, ssap);
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_proc_rx_pdu
**
** Description      Process PDU for data link
**
** Returns          void
**
*******************************************************************************/
void llcp_dlc_proc_rx_pdu(uint8_t dsap, uint8_t ptype, uint8_t ssap,
                          uint16_t length, uint8_t* p_data) {
  tLLCP_DLCB* p_dlcb;

  DLOG_IF(INFO, nfc_debug_enabled)
      << StringPrintf("DSAP:0x%x, PTYPE:0x%x, SSAP:0x%x", dsap, ptype, ssap);

  if (dsap == LLCP_SAP_LM) {
    LOG(ERROR) << StringPrintf("Invalid SAP:0x%x for PTYPE:0x%x", dsap, ptype);
    return;
  }

  switch (ptype) {
    case LLCP_PDU_CONNECT_TYPE:
      llcp_dlc_proc_connect_pdu(dsap, ssap, length, p_data);
      break;

    case LLCP_PDU_DISC_TYPE:
      llcp_dlc_proc_disc_pdu(dsap, ssap, length);
      break;

    case LLCP_PDU_CC_TYPE:
      llcp_dlc_proc_cc_pdu(dsap, ssap, length, p_data);
      break;

    case LLCP_PDU_DM_TYPE:
      llcp_dlc_proc_dm_pdu(dsap, ssap, length, p_data);
      break;

    case LLCP_PDU_FRMR_TYPE:
      p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
      if (p_dlcb) {
        llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
      }
      break;

    case LLCP_PDU_RR_TYPE:
    case LLCP_PDU_RNR_TYPE:
      llcp_dlc_proc_rr_rnr_pdu(dsap, ptype, ssap, length, p_data);
      break;

    default:
      LOG(ERROR) << StringPrintf("Unexpected PDU type (0x%x)", ptype);

      p_dlcb = llcp_dlc_find_dlcb_by_sap(dsap, ssap);
      if (p_dlcb) {
        llcp_util_send_frmr(p_dlcb, LLCP_FRMR_W_ERROR_FLAG, ptype, 0);
        llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_FRAME_ERROR, NULL);
      }
      break;
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_check_to_send_rr_rnr
**
** Description      Send RR or RNR if necessary
**
** Returns          void
**
*******************************************************************************/
void llcp_dlc_check_to_send_rr_rnr(void) {
  uint8_t idx;
  bool flush = true;

  DLOG_IF(INFO, nfc_debug_enabled) << __func__;

  /*
  ** DLC doesn't send RR PDU for each received I PDU because multiple I PDUs
  ** can be aggregated in a received AGF PDU. In this case, this is post
  ** processing of AGF PDU to send single RR or RNR after processing all I
  ** PDUs in received AGF if there was no I-PDU to carry N(R).
  **
  ** Send RR or RNR if any change of local busy condition or rx congestion
  ** status, or V(RA) is not V(R).
  */
  for (idx = 0; idx < LLCP_MAX_DATA_LINK; idx++) {
    if (llcp_cb.dlcb[idx].state == LLCP_DLC_STATE_CONNECTED) {
      llcp_util_send_rr_rnr(&(llcp_cb.dlcb[idx]));

      /* check flag to send DISC when tx queue is empty */
      if (llcp_cb.dlcb[idx].flags & LLCP_DATA_LINK_FLAG_PENDING_DISC) {
        /* if no pending data and all PDU is acked */
        if ((llcp_cb.dlcb[idx].i_xmit_q.count == 0) &&
            (llcp_cb.dlcb[idx].next_rx_seq == llcp_cb.dlcb[idx].sent_ack_seq) &&
            (llcp_cb.dlcb[idx].next_tx_seq == llcp_cb.dlcb[idx].rcvd_ack_seq)) {
          llcp_cb.dlcb[idx].flags &= ~LLCP_DATA_LINK_FLAG_PENDING_DISC;
          llcp_dlsm_execute(&(llcp_cb.dlcb[idx]),
                            LLCP_DLC_EVENT_API_DISCONNECT_REQ, &flush);
        }
      }
    }
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_is_rw_open
**
** Description      check if receive window is open in remote
**
** Returns          TRUE if remote can receive more data
**
*******************************************************************************/
bool llcp_dlc_is_rw_open(tLLCP_DLCB* p_dlcb) {
  if ((uint8_t)(p_dlcb->next_tx_seq - p_dlcb->rcvd_ack_seq) % LLCP_SEQ_MODULO <
      p_dlcb->remote_rw) {
    return true;
  } else {
    DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
        "Flow Off, V(S):%d, V(SA):%d, RW(R):%d", p_dlcb->next_tx_seq,
        p_dlcb->rcvd_ack_seq, p_dlcb->remote_rw);
    return false;
  }
}

/*******************************************************************************
**
** Function         llcp_dlc_get_next_pdu
**
** Description      Get a PDU from tx queue of data link
**
** Returns          NFC_HDR*
**
*******************************************************************************/
NFC_HDR* llcp_dlc_get_next_pdu(tLLCP_DLCB* p_dlcb) {
  NFC_HDR* p_msg = NULL;
  bool flush = true;
  tLLCP_SAP_CBACK_DATA data;

  uint8_t send_seq = p_dlcb->next_tx_seq;

  /* if there is data to send and remote device can receive it */
  if ((p_dlcb->i_xmit_q.count) && (!p_dlcb->remote_busy) &&
      (llcp_dlc_is_rw_open(p_dlcb))) {
    p_msg = (NFC_HDR*)GKI_dequeue(&p_dlcb->i_xmit_q);
    llcp_cb.total_tx_i_pdu--;

    if (p_msg->offset >= LLCP_MIN_OFFSET) {
      /* add LLCP header, DSAP, PTYPE, SSAP, N(S), N(R) and update sent_ack_seq,
       * V(RA) */
      llcp_util_build_info_pdu(p_dlcb, p_msg);

      p_dlcb->next_tx_seq = (p_dlcb->next_tx_seq + 1) % LLCP_SEQ_MODULO;

      DLOG_IF(INFO, nfc_debug_enabled) << StringPrintf(
          "LLCP TX - N(S,R):(%d,%d) V(S,SA,R,RA):(%d,%d,%d,%d)", send_seq,
          p_dlcb->next_rx_seq, p_dlcb->next_tx_seq, p_dlcb->rcvd_ack_seq,
          p_dlcb->next_rx_seq, p_dlcb->sent_ack_seq);
    } else {
      LOG(ERROR) << StringPrintf("offset (%d) must be %d at least",
                                 p_msg->offset, LLCP_MIN_OFFSET);
      GKI_freebuf(p_msg);
      p_msg = NULL;
    }
  }

  /* if tx queue is empty and all PDU is acknowledged */
  if ((p_dlcb->i_xmit_q.count == 0) &&
      (p_dlcb->next_rx_seq == p_dlcb->sent_ack_seq) &&
      (p_dlcb->next_tx_seq == p_dlcb->rcvd_ack_seq)) {
    /* check flag to send DISC */
    if (p_dlcb->flags & LLCP_DATA_LINK_FLAG_PENDING_DISC) {
      p_dlcb->flags &= ~LLCP_DATA_LINK_FLAG_PENDING_DISC;
      llcp_dlsm_execute(p_dlcb, LLCP_DLC_EVENT_API_DISCONNECT_REQ, &flush);
    }

    /* check flag to notify upper layer */
    if (p_dlcb->flags & LLCP_DATA_LINK_FLAG_NOTIFY_TX_DONE) {
      p_dlcb->flags &= ~LLCP_DATA_LINK_FLAG_NOTIFY_TX_DONE;

      data.tx_complete.event = LLCP_SAP_EVT_TX_COMPLETE;
      data.tx_complete.local_sap = p_dlcb->local_sap;
      data.tx_complete.remote_sap = p_dlcb->remote_sap;

      (*p_dlcb->p_app_cb->p_app_cback)(&data);
    }
  }

  return p_msg;
}

/*******************************************************************************
**
** Function         llcp_dlc_get_next_pdu_length
**
** Description      return length of PDU which is top in tx queue of data link
**
** Returns          length of PDU
**
*******************************************************************************/
uint16_t llcp_dlc_get_next_pdu_length(tLLCP_DLCB* p_dlcb) {
  NFC_HDR* p_msg;

  /* if there is data to send and remote device can receive it */
  if ((p_dlcb->i_xmit_q.count) && (!p_dlcb->remote_busy) &&
      (llcp_dlc_is_rw_open(p_dlcb))) {
    p_msg = (NFC_HDR*)p_dlcb->i_xmit_q.p_first;

    return (p_msg->len + LLCP_PDU_HEADER_SIZE + LLCP_SEQUENCE_SIZE);
  }
  return 0;
}

/*******************************************************************************
**
** Function         llcp_dlsm_get_state_name
**
** Description      This function returns the state name.
**
** Returns          pointer to the name
**
*******************************************************************************/
static std::string llcp_dlsm_get_state_name(tLLCP_DLC_STATE state) {
  switch (state) {
    case LLCP_DLC_STATE_IDLE:
      return "IDLE";
    case LLCP_DLC_STATE_W4_REMOTE_RESP:
      return "W4_REMOTE_RESP";
    case LLCP_DLC_STATE_W4_LOCAL_RESP:
      return "W4_LOCAL_RESP";
    case LLCP_DLC_STATE_CONNECTED:
      return "CONNECTED";
    case LLCP_DLC_STATE_W4_REMOTE_DM:
      return "W4_REMOTE_DM";
    default:
      return "???? UNKNOWN STATE";
  }
}

/*******************************************************************************
**
** Function         llcp_dlsm_get_event_name
**
** Description      This function returns the event name.
**
** Returns          pointer to the name
**
*******************************************************************************/
static std::string llcp_dlsm_get_event_name(tLLCP_DLC_EVENT event) {
  switch (event) {
    case LLCP_DLC_EVENT_API_CONNECT_REQ:
      return "API_CONNECT_REQ";
    case LLCP_DLC_EVENT_API_CONNECT_CFM:
      return "API_CONNECT_CFM";
    case LLCP_DLC_EVENT_API_CONNECT_REJECT:
      return "API_CONNECT_REJECT";
    case LLCP_DLC_EVENT_PEER_CONNECT_IND:
      return "PEER_CONNECT_IND";
    case LLCP_DLC_EVENT_PEER_CONNECT_CFM:
      return "PEER_CONNECT_CFM";
    case LLCP_DLC_EVENT_API_DATA_REQ:
      return "API_DATA_REQ";
    case LLCP_DLC_EVENT_PEER_DATA_IND:
      return "PEER_DATA_IND";
    case LLCP_DLC_EVENT_API_DISCONNECT_REQ:
      return "API_DISCONNECT_REQ";
    case LLCP_DLC_EVENT_PEER_DISCONNECT_IND:
      return "PEER_DISCONNECT_IND";
    case LLCP_DLC_EVENT_PEER_DISCONNECT_RESP:
      return "PEER_DISCONNECT_RESP";
    case LLCP_DLC_EVENT_FRAME_ERROR:
      return "FRAME_ERROR";
    case LLCP_DLC_EVENT_LINK_ERROR:
      return "LINK_ERROR";
    case LLCP_DLC_EVENT_TIMEOUT:
      return "TIMEOUT";
    default:
      return "???? UNKNOWN EVENT";
  }
}