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Haavard Skinnemoenab0df362008-08-29 21:09:49 +02001AVR32 Port multiplexer configuration
2====================================
3
4On AVR32 chips, most external I/O pins are routed through a port
5multiplexer. There are currently two kinds of port multiplexer
6hardware around with different register interfaces:
7
8 * PIO (AT32AP700x; this is also used on ARM AT91 chips)
9 * GPIO (all other AVR32 chips)
10
11The "PIO" variant supports multiplexing up to two peripherals per pin
12in addition to GPIO (software control). Each pin has configurable
13pull-up, glitch filter, interrupt and multi-drive capabilities.
14
15The "GPIO" variant supports multiplexing up to four peripherals per
16pin in addition to GPIO. Each pin has configurable
17pull-up/pull-down/buskeeper, glitch filter, interrupt, open-drain and
18schmitt-trigger capabilities, as well as configurable drive strength
19and slew rate control.
20
21Both controllers are configured using the same API, but the functions
22may accept different values for some parameters depending on the
23actual portmux implementation, and some parameters may be ignored by
24one of the implementation (e.g. the "PIO" implementation will ignore
25the drive strength flags since the hardware doesn't support
26configurable drive strength.)
27
28Selecting the portmux implementation
29------------------------------------
30Since u-boot is lacking a Kconfig-style configuration engine, the
31portmux implementation must be selected manually by defining one of
32the following symbols:
33
34 CONFIG_PORTMUX_PIO
35 CONFIG_PORTMUX_GPIO
36
37depending on which implementation the chip in question uses.
38
39Identifying pins
40----------------
41The portmux configuration functions described below identify the pins
42to act on based on two parameters: A "port" (i.e. a block of pins
43that somehow belong together) and a pin mask. Both are defined in an
44implementation-specific manner.
45
46The available ports are defined on the form
47
48 #define PORTMUX_PORT_A (something)
49
50where "A" matches the identifier given in the chip's data sheet, and
51"something" is whatever the portmux implementation needs to identify
52the port (usually a memory address).
53
54The pin mask is a bitmask where each '1' bit indicates a pin to apply
55the current operation to. The width of the bitmask may vary from port
56to port, but it is never wider than 32 bits (which is the width of
57'unsigned long' on avr32).
58
59Selecting functions
60-------------------
61Each pin can either be assigned to one of a predefined set of on-chip
62peripherals, or it can be set up to be controlled by software. For the
63former case, the portmux implementation defines an enum containing all
64the possible peripheral functions that can be selected. For example,
65the PIO implementation, which allows multiplexing two peripherals per
66pin, defines it like this:
67
68 enum portmux_function {
69 PORTMUX_FUNC_A,
70 PORTMUX_FUNC_B,
71 };
72
73To configure a set of pins to be connected to a given peripheral
74function, the following function is used.
75
76 void portmux_select_peripheral(void *port, unsigned long pin_mask,
77 enum portmux_function func, unsigned long flags);
78
79To configure a set of pins to be controlled by software (GPIO), the
80following function is used. In this case, no "function" argument is
81required since "GPIO" is a function in its own right.
82
83 void portmux_select_gpio(void *port, unsigned int pin_mask,
84 unsigned long flags);
85
86Both of these functions take a "flags" parameter which may be used to
87alter the default configuration of the pin. This is a bitmask of
88various flags defined in an implementation-specific way, but the names
89of the flags are the same on all implementations.
90
91 PORTMUX_DIR_OUTPUT
92 PORTMUX_DIR_INPUT
93
Thomas Weberc46bf092012-03-24 22:44:01 +000094These mutually-exclusive flags configure the initial direction of the
Haavard Skinnemoenab0df362008-08-29 21:09:49 +020095pins. PORTMUX_DIR_OUTPUT means that the pins are driven by the CPU,
96while PORTMUX_DIR_INPUT means that the pins are tristated by the CPU.
97These flags are ignored by portmux_select_peripheral().
98
99 PORTMUX_INIT_HIGH
100 PORTMUX_INIT_LOW
101
102These mutually-exclusive flags configure the initial state of the
103pins: High (Vdd) or low (Vss). They are only effective when
104portmux_select_gpio() is called with the PORTMUX_DIR_OUTPUT flag set.
105
106 PORTMUX_PULL_UP
107 PORTMUX_PULL_DOWN
108 PORTMUX_BUSKEEPER
109
110These mutually-exclusive flags are used to enable any on-chip CMOS
111resistors connected to the pins. PORTMUX_PULL_UP causes the pins to be
112pulled up to Vdd, PORTMUX_PULL_DOWN causes the pins to be pulled down
113to Vss, and PORTMUX_BUSKEEPER will keep the pins in whatever state
114they were left in by whatever was driving them last. If none of the
115flags are specified, the pins are left floating if no one are driving
116them; this is only recommended for always-output pins (e.g. extern
117address and control lines driven by the CPU.)
118
119Note that the "PIO" implementation will silently ignore the
120PORTMUX_PULL_DOWN flag and interpret PORTMUX_BUSKEEPER as
121PORTMUX_PULL_UP.
122
123 PORTMUX_DRIVE_MIN
124 PORTMUX_DRIVE_LOW
125 PORTMUX_DRIVE_HIGH
126 PORTMUX_DRIVE_MAX
127
Thomas Weberc46bf092012-03-24 22:44:01 +0000128These mutually-exclusive flags determine the drive strength of the
Haavard Skinnemoenab0df362008-08-29 21:09:49 +0200129pins. PORTMUX_DRIVE_MIN will give low power-consumption, but may cause
130corruption of high-speed signals. PORTMUX_DRIVE_MAX will give high
131power-consumption, but may be necessary on pins toggling at very high
132speeds. PORTMUX_DRIVE_LOW and PORTMUX_DRIVE_HIGH specify something in
133between the other two.
134
135Note that setting the drive strength too high may cause excessive
136overshoot and EMI problems, which may in turn cause signal corruption.
137Also note that the "PIO" implementation will silently ignore these
138flags.
139
140 PORTMUX_OPEN_DRAIN
141
142This flag will configure the pins as "open drain", i.e. setting the
143pin state to 0 will drive it low, while setting it to 1 will leave it
144floating (or, in most cases, let it be pulled high by an internal or
145external pull-up resistor.) In the data sheet for chips using the
146"PIO" variant, this mode is called "multi-driver".
147
148Enabling specific peripherals
149-----------------------------
150In addition to the above functions, each chip provides a set of
151functions for setting up the port multiplexer to use a given
152peripheral. The following are some of the functions available.
153
154All the functions below take a "drive_strength" parameter, which must
155be one of the PORTMUX_DRIVE_x flags specified above. Any other
156portmux flags will be silently filtered out.
157
158To set up the External Bus Interface (EBI), call
159
160 void portmux_enable_ebi(unsigned int bus_width,
161 unsigned long flags, unsigned long drive_strength)
162
163where "bus_width" must be either 16 or 32. "flags" can be any
164combination of the following flags.
165
166 PORTMUX_EBI_CS(x) /* Enable chip select x */
167 PORTMUX_EBI_NAND /* Enable NAND flash interface */
168 PORTMUX_EBI_CF(x) /* Enable CompactFlash interface x */
169 PORTMUX_EBI_NWAIT /* Enable NWAIT signal */
170
171To set up a USART, call
172
173 void portmux_enable_usartX(unsigned long drive_strength);
174
175where X is replaced by the USART instance to be configured.
176
177To set up an ethernet MAC:
178
179 void portmux_enable_macbX(unsigned long flags,
180 unsigned long drive_strength);
181
182where X is replaced by the MACB instance to be configured. "flags" can
183be any combination of the following flags.
184
185 PORTMUX_MACB_RMII /* Just set up the RMII interface */
186 PORTMUX_MACB_MII /* Set up full MII interface */
187 PORTMUX_MACB_SPEED /* Enable the SPEED pin */
188
189To set up the MMC controller:
190
191 void portmux_enable_mmci(unsigned long slot, unsigned long flags
192 unsigned long drive_strength);
193
194where "slot" identifies which of the alternative SD card slots to
195enable. "flags" can be any combination of the following flags:
196
197 PORTMUX_MMCI_4BIT /* Enable 4-bit SD card interface */
198 PORTMUX_MMCI_8BIT /* Enable 8-bit MMC+ interface */
199 PORTMUX_MMCI_EXT_PULLUP /* Board has external pull-ups */
200
201To set up a SPI controller:
202
203 void portmux_enable_spiX(unsigned long cs_mask,
204 unsigned long drive_strength);
205
206where X is replaced by the SPI instance to be configured. "cs_mask" is
207a 4-bit bitmask specifying which of the four standard chip select
208lines to set up as GPIOs.