Configuring ext signals

Pin functions (mux)

By default the UART2 pins are set up as GPIOs, and UART3 is set up as an UART. The following describes how to change pin functions under a 3.2 kernel.

Setup

As root,

mkdir /debug
mount -t debugfs none /debug

In the /debug/omap_mux directory which appears, the files relevant to the EXT connector are uart2_cts, uart2_rts, uart2_rx, uart2_tx, uart3_rx_irrx, uart3_tx_irtx. They are mapped to the pad configuration registers. Reading one of these files reports the current configuration of the pin. Writing the appropriate pattern to the file changes the configuration of the pin.

Pad Configuration Register

As described in OMAP35x Technical Reference Manual (Rev. Y), section 7.4.4 [1]

Bits	Name	Comments
15	WAKEUPEVENT
14	WAKEUPENABLE
13	OFFPULLTYPESELECT
12	OFFPULLUDENABLE
11	OFFOUTVALUE
10	OFFOUTENABLE
9	OFFENABLE
8	INPUTENABLE	0: output only. 1: bidirectional.
7,6,5	RESERVED
4	PULLTYPESELECT	0: pull-down. 1: pull-up.
3	PULLUDENABLE	0: pull not active. 1: pull active if pin not configured as output.
2,1,0	MUXMODE	See table below.

Mux modes

Mode 0	Mode 1	Mode 2	Mode 3	Mode 4	Mode 5	Mode 6	Mode 7
uart2_cts	mcbsp3_dx	gpt9_pwm_evt	NA	gpio_144	NA	NA	safe_mode
uart2_rts	mcbsp3_dr	gpt10_pwm_evt	NA	gpio_145	NA	NA	safe_mode
uart2_tx	mcbsp3_clkx	gpt11_pwm_evt	NA	gpio_146	NA	NA	safe_mode
uart2_rx	mcbsp3_fsx	gpt8_pwm_evt	NA	gpio_147	NA	NA	safe_mode
uart3_rx_irrx	NA	NA	NA	gpio_165	NA	NA	safe_mode
uart3_tx_irtx	NA	NA	NA	gpio_166	NA	NA	safe_mode

Example

Example of changing UART2_RTS from GPIO to UART mode [2]:

# cat /debug/omap_mux/uart2_rts
name: uart2_rts.gpio_145 (0x48002176/0x146 = 0x010c), b ab25, t NA
mode: OMAP_PIN_INPUT_PULLDOWN | OMAP_MUX_MODE4
signals: uart2_rts | mcbsp3_dr | gpt10_pwm_evt | NA | gpio_145 | NA | NA | safe_mode

# echo 0x0108 > /debug/omap_mux/uart2_rts
# cat /debug/omap_mux/uart2_rts
name: uart2_rts.uart2_rts (0x48002176/0x146 = 0x0108), b ab25, t NA
mode: OMAP_PIN_INPUT_PULLDOWN | OMAP_MUX_MODE0
signals: uart2_rts | mcbsp3_dr | gpt10_pwm_evt | NA | gpio_145 | NA | NA | safe_mode

The value was changed from 0x010c to 0x0108. In both numbers, bit8 is 1 for input enable, bit4 is 0 for pull-down, and bit3 is 1 for pull enable. Bits 2,1,0 changed from 4 to 0, which changed the mux mode from 4 to 0.

Power supply

Currently always set to supply 2.8V, changing this requires patching bootloaders (xload and u-boot).

This is connected to VAUX3 supply on PMIC, with these programmable voltages (200mA max): 1.5V, 1.8V, 2.5V, 2.8V and 3.0V, with 2.8V as default.

warning: at the time of this writing, both bootloaders (xload and u-boot) set this to 2.8V unconditionally, so don't rely on this providing other voltages during reboot until you patch both bootloaders.

GPIOs

Can be controlled using GPIO sysfs class device, as described in beagleboard tutorials here.

The pins must be set as GPIO using the pin mux.

In the following commands, NNN is the GPIO number, e.g. 145.

#enable gpioNNN folder, to prepare for the other commands
echo NNN > /sys/class/gpio/export

#reads "in" or "out" depending on what was written to it
cat /sys/class/gpio/gpioNNN/direction

#when direction is "out", reads 0 or 1 depending on what was written to it
#when pinmux specifies bidirectional and direction is "in", reads 0 or 1 depending on voltage at pin
#when pinmux specifies output-only and direction is "in", always reads 0
cat /sys/class/gpio/gpioNNN/value

#set value to 0, i.e. output low (only works when direction is "out")
echo 0 > /sys/class/gpio/gpioNNN/value

#set value to 1, i.e. output high (only works when direction is "out")
echo 1 > /sys/class/gpio/gpioNNN/value

#set direction to "in"
echo in > /sys/class/gpio/gpioNNN/direction

#set direction to "out" and value to 0, i.e. output low 
echo out > /sys/class/gpio/gpioNNN/direction

#set direction to "out" and value to 1, i.e. output high
echo high > /sys/class/gpio/gpioNNN/direction

#set direction to "out" and value to 0, i.e. output low 
echo low > /sys/class/gpio/gpioNNN/direction

#disable gpioNNN folder
echo NNN > /sys/class/gpio/unexport

UART3

On older firmwares, kernel messages are directed there. SuperZaxxon or later have that disabled.

On all firmwares released so far terminal with a shell is attached to UART3. The port runs at 115200 8N1 baud rate.

Disabling kernel messages

To disable kernel mesages, you need to edit kernel boot arguments. Probably easiest way to do it is to create autoboot.txt and place on root directory of a card in slot1 with this content:

setenv bootargs ubi.mtd=4 ubi.mtd=3 root=ubi0:rootfs rootfstype=ubifs rw rootflags=bulk_read

Alternatives are using u-boot environment (configure through USB or UART3 serial before system boots up) or patching and reflashing u-boot itself.

Disabling attached terminal

For this you need to edit /etc/inittab on pandora rootfs and comment out these lines:

#S0:2345:once:/sbin/getty 115200 ttyS0
#O2:2345:once:/sbin/getty 115200 ttyO2