Difference between revisions of "Duovero Multiplexes"

Latest revision as of 05:24, 26 September 2014

This wiki entry concentrates on the Duovero Parlor board and the Multiplexes available from the 40 pin connector.

The ground pin is nearest the console connector port and the power pins are nearest the centre of the board. This is as of writing but it is highly recommended that you check before connecting! Use a voltmeter to check the 3.3V, 5V and 1.8V pins to familiarise yourself with the layout.

There are also two connections on the Parlor board:

OMAP Pin	GPIO #	Purpose
AG24	GPIO121	user push button
AH24	GPIO122	user LED

You should start your journey here.

The primary reference for multiplexes and pin functions is the Texas Instruments OMAP4 technical reference manual. The short version of that 6000 page manual is the OMAP4430 datasheet which is easier to search. The primary source reference is in the Uboot code, specifically duovero_mux_data.h which uses the defines from ./arch/arm/include/asm/arch-omap4/mux_omap4.h.

Software Muxing

A helpful post from Phil Lutz describes how multiplexing can be explored without kernel recompilation. The default multiplex for the user LED may not be set to GPIO in Uboot. It certainly is not set to GPIO by the OMAP itself. You can look at the OMAP datasheet on page 48 you can see that the official name for GPIO 122 pin is "abe_dmic_din3" (Mode 0 names are accepted pin names).

This information can also be found by searching for "gpio_122" in the board pinmuxing configuration stored in sysfs: /sys/kernel/debug/omap_mux/board/core. Every pin which can be configured as gpio has a hint about that.

So now just check which is the current pinmuxing configuration for this pin by:

$ cat /sys/kernel/debug/omap_mux/abe_dmic_din3 
name: abe_dmic_din3.abe_dmic_din3 (0x4a100116/0x116 = 0x0100), b ah24, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE0
signals: abe_dmic_din3 | slimbus2_data | abe_dmic_clk2 | gpio_122 | NA | dmtimer9_pwm_evt | NA | safe_mode

As the output suggests, the pin is configured in MODE0, this is 'abe_dmic_din3'. The other modes are listed in order as they appear in the OMAP data manual. gpio_122 is multiplex MODE 3. You can set it with:

 $ echo 3 > /sys/kernel/debug/omap_mux/abe_dmic_din3

Now you can turn on and off the LED using the usual gpio configuration in /sys/class/gpio/ (google it!). Note that "echo 3" does more than set Mode 3. The number is a selection of bits that set various states for the pin. A quick summary is:

Bit 0,1,2	Set the mode
Bit 3	0 = pull up/down disabled , 1 = enabled
Bit 4	0 = pull down, 1 = pull up
Bit 8	0 = Output only. 1 = input enable (bidirectional)

There are more but these are for sleep modes and wakeup. The manual has details. The defines in mux_omap4.h are useful for interpreting the duovero_mux_data.h file:

IEN	1 << 8	Input enable (bidirectional)
IDIS	0 << 8	Output only
PTU	3 << 3	Enable Pullup
PTD	1 << 3	Enable Pulldown
EN	1 << 3	PU/PD enable
DIS	0 << 3	PU/PD disable

Parlor pin mux table

To assist in figuring out which pins on the Parlor board can be assigned to which duties, here's a table of functions. Mode 7 is "safe_mode" where the pin is effectively disconnected from any functionality. It's set to high impedance (Z) and is left out of the table. The bolded functions are those set by the current U-Boot duovero_mux_data.h. This file sets other parameters (eg: output only, disable pullup/pulldown, etc) and you must refer to the U-Boot file to know what the full state is. A partial indication of the state (wake mode) is indicated in the table by arrows (bidirectional, output, pullup, pulldown).

Underneath the Connector entries are the IOPAD mux address offsets and under each gpio entry is the corresponding GPIO register and bit offset. These numbers are useful for device tree purposes. The gpio numbers are calculated simply as: register = int(gpionumber / 32) + 1 and offset = gpionumber % 32.

Notes

a) Assigned as such in u-boot but reassigned in the kernel board startup code to Mode 3 Outputs

b) There is a 10K pull up to 1.8V, internal to the DuoVero COM, on the HDQ_SIO line. Do not enable a pull down on this line. This will result in a non-logic output level (approximately 1V). This is currently considered to be a bug and may be removed in future COM revisions.

c) There are pullups on I2C2 and I2C3 of approximately 1K. S/C current is over 2mA.