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- AVR32 Port multiplexer configuration
- ====================================
- On AVR32 chips, most external I/O pins are routed through a port
- multiplexer. There are currently two kinds of port multiplexer
- hardware around with different register interfaces:
- * PIO (AT32AP700x; this is also used on ARM AT91 chips)
- * GPIO (all other AVR32 chips)
- The "PIO" variant supports multiplexing up to two peripherals per pin
- in addition to GPIO (software control). Each pin has configurable
- pull-up, glitch filter, interrupt and multi-drive capabilities.
- The "GPIO" variant supports multiplexing up to four peripherals per
- pin in addition to GPIO. Each pin has configurable
- pull-up/pull-down/buskeeper, glitch filter, interrupt, open-drain and
- schmitt-trigger capabilities, as well as configurable drive strength
- and slew rate control.
- Both controllers are configured using the same API, but the functions
- may accept different values for some parameters depending on the
- actual portmux implementation, and some parameters may be ignored by
- one of the implementation (e.g. the "PIO" implementation will ignore
- the drive strength flags since the hardware doesn't support
- configurable drive strength.)
- Selecting the portmux implementation
- ------------------------------------
- Since u-boot is lacking a Kconfig-style configuration engine, the
- portmux implementation must be selected manually by defining one of
- the following symbols:
- CONFIG_PORTMUX_PIO
- CONFIG_PORTMUX_GPIO
- depending on which implementation the chip in question uses.
- Identifying pins
- ----------------
- The portmux configuration functions described below identify the pins
- to act on based on two parameters: A "port" (i.e. a block of pins
- that somehow belong together) and a pin mask. Both are defined in an
- implementation-specific manner.
- The available ports are defined on the form
- #define PORTMUX_PORT_A (something)
- where "A" matches the identifier given in the chip's data sheet, and
- "something" is whatever the portmux implementation needs to identify
- the port (usually a memory address).
- The pin mask is a bitmask where each '1' bit indicates a pin to apply
- the current operation to. The width of the bitmask may vary from port
- to port, but it is never wider than 32 bits (which is the width of
- 'unsigned long' on avr32).
- Selecting functions
- -------------------
- Each pin can either be assigned to one of a predefined set of on-chip
- peripherals, or it can be set up to be controlled by software. For the
- former case, the portmux implementation defines an enum containing all
- the possible peripheral functions that can be selected. For example,
- the PIO implementation, which allows multiplexing two peripherals per
- pin, defines it like this:
- enum portmux_function {
- PORTMUX_FUNC_A,
- PORTMUX_FUNC_B,
- };
- To configure a set of pins to be connected to a given peripheral
- function, the following function is used.
- void portmux_select_peripheral(void *port, unsigned long pin_mask,
- enum portmux_function func, unsigned long flags);
- To configure a set of pins to be controlled by software (GPIO), the
- following function is used. In this case, no "function" argument is
- required since "GPIO" is a function in its own right.
- void portmux_select_gpio(void *port, unsigned int pin_mask,
- unsigned long flags);
- Both of these functions take a "flags" parameter which may be used to
- alter the default configuration of the pin. This is a bitmask of
- various flags defined in an implementation-specific way, but the names
- of the flags are the same on all implementations.
- PORTMUX_DIR_OUTPUT
- PORTMUX_DIR_INPUT
- These mutually-exclusive flags configure the initial direction of the
- pins. PORTMUX_DIR_OUTPUT means that the pins are driven by the CPU,
- while PORTMUX_DIR_INPUT means that the pins are tristated by the CPU.
- These flags are ignored by portmux_select_peripheral().
- PORTMUX_INIT_HIGH
- PORTMUX_INIT_LOW
- These mutually-exclusive flags configure the initial state of the
- pins: High (Vdd) or low (Vss). They are only effective when
- portmux_select_gpio() is called with the PORTMUX_DIR_OUTPUT flag set.
- PORTMUX_PULL_UP
- PORTMUX_PULL_DOWN
- PORTMUX_BUSKEEPER
- These mutually-exclusive flags are used to enable any on-chip CMOS
- resistors connected to the pins. PORTMUX_PULL_UP causes the pins to be
- pulled up to Vdd, PORTMUX_PULL_DOWN causes the pins to be pulled down
- to Vss, and PORTMUX_BUSKEEPER will keep the pins in whatever state
- they were left in by whatever was driving them last. If none of the
- flags are specified, the pins are left floating if no one are driving
- them; this is only recommended for always-output pins (e.g. extern
- address and control lines driven by the CPU.)
- Note that the "PIO" implementation will silently ignore the
- PORTMUX_PULL_DOWN flag and interpret PORTMUX_BUSKEEPER as
- PORTMUX_PULL_UP.
- PORTMUX_DRIVE_MIN
- PORTMUX_DRIVE_LOW
- PORTMUX_DRIVE_HIGH
- PORTMUX_DRIVE_MAX
- These mutually-exclusive flags determine the drive strength of the
- pins. PORTMUX_DRIVE_MIN will give low power-consumption, but may cause
- corruption of high-speed signals. PORTMUX_DRIVE_MAX will give high
- power-consumption, but may be necessary on pins toggling at very high
- speeds. PORTMUX_DRIVE_LOW and PORTMUX_DRIVE_HIGH specify something in
- between the other two.
- Note that setting the drive strength too high may cause excessive
- overshoot and EMI problems, which may in turn cause signal corruption.
- Also note that the "PIO" implementation will silently ignore these
- flags.
- PORTMUX_OPEN_DRAIN
- This flag will configure the pins as "open drain", i.e. setting the
- pin state to 0 will drive it low, while setting it to 1 will leave it
- floating (or, in most cases, let it be pulled high by an internal or
- external pull-up resistor.) In the data sheet for chips using the
- "PIO" variant, this mode is called "multi-driver".
- Enabling specific peripherals
- -----------------------------
- In addition to the above functions, each chip provides a set of
- functions for setting up the port multiplexer to use a given
- peripheral. The following are some of the functions available.
- All the functions below take a "drive_strength" parameter, which must
- be one of the PORTMUX_DRIVE_x flags specified above. Any other
- portmux flags will be silently filtered out.
- To set up the External Bus Interface (EBI), call
- void portmux_enable_ebi(unsigned int bus_width,
- unsigned long flags, unsigned long drive_strength)
- where "bus_width" must be either 16 or 32. "flags" can be any
- combination of the following flags.
- PORTMUX_EBI_CS(x) /* Enable chip select x */
- PORTMUX_EBI_NAND /* Enable NAND flash interface */
- PORTMUX_EBI_CF(x) /* Enable CompactFlash interface x */
- PORTMUX_EBI_NWAIT /* Enable NWAIT signal */
- To set up a USART, call
- void portmux_enable_usartX(unsigned long drive_strength);
- where X is replaced by the USART instance to be configured.
- To set up an ethernet MAC:
- void portmux_enable_macbX(unsigned long flags,
- unsigned long drive_strength);
- where X is replaced by the MACB instance to be configured. "flags" can
- be any combination of the following flags.
- PORTMUX_MACB_RMII /* Just set up the RMII interface */
- PORTMUX_MACB_MII /* Set up full MII interface */
- PORTMUX_MACB_SPEED /* Enable the SPEED pin */
- To set up the MMC controller:
- void portmux_enable_mmci(unsigned long slot, unsigned long flags
- unsigned long drive_strength);
- where "slot" identifies which of the alternative SD card slots to
- enable. "flags" can be any combination of the following flags:
- PORTMUX_MMCI_4BIT /* Enable 4-bit SD card interface */
- PORTMUX_MMCI_8BIT /* Enable 8-bit MMC+ interface */
- PORTMUX_MMCI_EXT_PULLUP /* Board has external pull-ups */
- To set up a SPI controller:
- void portmux_enable_spiX(unsigned long cs_mask,
- unsigned long drive_strength);
- where X is replaced by the SPI instance to be configured. "cs_mask" is
- a 4-bit bitmask specifying which of the four standard chip select
- lines to set up as GPIOs.
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