AM6546: Writing to GPO from PRU

Hi Nick,

So would I be right in saying, that without any changes in the device-tree we should be able to write to the GPO register and get an output?

Dhruva,

To help us better assist you, please provide us some details:

• Which ICSSG?
• Which PRU?
• Which GPO?
• What values have been written to what registers?
• How are you checking the result, i.e. what pin are you looking at?
• What is the pinmux value for that pin?

Thanks,
Brad

Brad,

We were working with "PRG0_PRU0_GPO18" design signal pad name. Ball number 25. 

We also tried to configure it as a GPIO (Muxmode 7 - GPIO1_47 <default> ) without our additional ADC circuitry.

We added the following to &main_pmx0

mygpio1_pins_default: mygpio1_pins_default {
pinctrl-single,pins = <
AM65X_IOPAD(0x023c, PIN_INPUT, 7) /* (V25) PRG0_PRU0_GPO18.GPIO1_47 */
>;
};

We were hoping to get this working and then change the pinmux value.

However after exposing the GPIO pin from the sysfs, we were unable to successfully write to it.  We were trying to echo 1 to the value-file of the gpio.

Dhruva Krishnadas said:

We were working with "PRG0_PRU0_GPO18" design signal pad name. Ball number 25. 

I assume you're talking about V25.

Dhruva Krishnadas said:

mygpio1_pins_default: mygpio1_pins_default {
pinctrl-single,pins = <
AM65X_IOPAD(0x023c, PIN_INPUT, 7) /* (V25) PRG0_PRU0_GPO18.GPIO1_47 */
>;
};

You might be used to AM3/4/5 where there was only an input enable bit.  On AM6 there are enable bits related to both input and output.  In order to output on that pin you need PIN_OUTPUT, and if you wish to be able to see what's on the pin you also need the input, i.e. PIN_INPUT | PIN_OUTPUT.

Please directly check the register value.  I see the following using the SDK 6.01 binaries:

root@am65xx-evm:~# devmem2 0x0011c23c
/dev/mem opened.
Memory mapped at address 0xffffb2830000.
Read at address 0x0011C23C (0xffffb283c23c): 0x08210007

That value corresponds to neither the input nor output being enabled.  I made a quick update using devmem2:

root@am65xx-evm:~# devmem2 0x0011c23c w 0x08050007
/dev/mem opened.
Memory mapped at address 0xffff893b0000.
Read at address 0x0011C23C (0xffff893bc23c): 0x08010007
Write at address 0x0011C23C (0xffff893bc23c): 0x08050007, readback 0x08050007

This new value enables both input and output.  Now you can modify the GPIO from user space.  Some quick notes regarding the GPIO:

• /sys/class/gpio/gpiochip0 -> Controls WKUP_GPIO[0-55]
• /sys/class/gpio/gpiochip56 -> Controls GPIO0[0-95]
• /sys/class/gpio/gpiochip152 -> Controls GPIO1[0-89]

In your case you are trying to control gpio1_47.  So in terms of the Linux GPIO's, gpio152 corresponds to gpio1_0.  Therefore gpio1_47 is Linux gpio199.  Here's how I write it:

root@am65xx-evm:~# cd /sys/class/gpio/
root@am65xx-evm:/sys/class/gpio# echo 199 > export

root@am65xx-evm:/sys/class/gpio# cd gpio199
root@am65xx-evm:/sys/class/gpio/gpio199# ls
active_low device direction edge power subsystem uevent value
root@am65xx-evm:/sys/class/gpio/gpio199# cat direction
in
root@am65xx-evm:/sys/class/gpio/gpio199# echo out > direction
root@am65xx-evm:/sys/class/gpio/gpio199# cat direction
out
root@am65xx-evm:/sys/class/gpio/gpio199# cat value
0
root@am65xx-evm:/sys/class/gpio/gpio199# echo 1 > value
root@am65xx-evm:/sys/class/gpio/gpio199# cat value
1

Best regards,
Brad

Thanks Brad. We were able to have reasonable success by modifying the pad configuration register (0x0011C23C) for ball number V25. We were able to output to the pin after setting muxmode as PRG0_PRU0_GPO18 (muxmode 0) and GPIO1_47 (muxmode 7) by setting pad configuration register using devmem2 program.

However, we were hoping to set the pad configuration register by simply having the dtb file changed. However using an updated dtb ( with  mode set to PIN_OUTPUT|PIN_INPUT ) did not change the value of the pad configuration register.

We also tried hard coding (without macros) 0x08010000 to the pad configuration register from the dts file but that did not work either.

Also, are the .h and .c files generated by the pinmux tool of any use?

Thanks a lot Brad. We'll give that a try.