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diff --git a/doc/README.AVR32-port-muxing b/doc/README.AVR32-port-muxing new file mode 100644 index 0000000..b53799d --- /dev/null +++ b/doc/README.AVR32-port-muxing @@ -0,0 +1,208 @@ +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-exlusive 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-exlusive 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. |