NFC: digital: Add NFC-DEP Initiator-side NACK Support
When an NFC-DEP Initiator receives a frame with
an incorrect CRC or with a parity error, and the
frame is at least 4 bytes long, its supposed to
send a NACK to the Target. The Initiator can
send up to 'N(retry,nack)' consecutive NACKs
where 2 <= 'N(retry,nack)' <= 5. When the limit
is exceeded, a PROTOCOL EXCEPTION is raised.
Any other type of transmission error is to be
ignored and the Initiator should continue
waiting for a new frame. This is described
in section 14.12.5.4 of the NFC Digital Protocol
Spec.
The digital layer's NFC-DEP code doesn't implement
any of this so add it. This support diverges from
the spec in two significant ways:
a) NACKs will be sent for ANY error reported by the
driver except a timeout. This is done because
there is currently no way for the digital layer
to distinguish a CRC or parity error from any
other type of error reported by the driver.
b) All other errors will cause a PROTOCOL EXCEPTION
even frames with CRC errors that are less than 4
bytes.
The value chosen for 'N(retry,nack)' is 2.
Targets do not send NACK PDUs.
Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
2 files changed