Q: GPIO FUNCSEL NULL = {0xf or 0x1f}?

[soundpaint]

• Tables 290 and 292 in the RP datasheet contain the following function categories:
  XIP = 0, SPI = 1, UART = 2, I2C = 3, PWM = 4, SIO = 5, PIO0 = 6, PIO1 = 7, GPCK = 8 , USB = 9
  (but no "NULL")

• Table 339 mentions additional "31 == NULL" .

• C SDK file gpio.h defines "enum gpio_function" with additional "NULL = 0xf" (in contrast to the above "31 == NULL").

Which is right?

[soundpaint]

And, by the way, since function gpio_set_function() in gpio.c seems to be not (yet?) implemented, function pio_gpio_init() in pio.h obviously has no effect at all. Is this behavior subject to be eventually changed, or can I safely ignore any call to function pio_gpio_init()? Or is there some compiler / linking magic that injects additional code?

[lurch]

Table 339 mentions additional "31 == NULL" .
C SDK file gpio.h defines "enum gpio_function" with additional "NULL = 0xf" (in contrast to the above "31 == NULL").
Which is right?

This is only a guess (until one of the hardware engineers comes along and gives us a better answer), but perhaps anything which isn't in the range 0 - 9 is "effectively NULL" ? (either that, or there's a typo and https://github.com/raspberrypi/pico-sdk/blob/develop/src/rp2_common/hardware_gpio/include/hardware/gpio.h#L99 was supposed to be GPIO_FUNC_NULL = 0x1f, 🤷‍♂️ )

And, by the way, since function gpio_set_function() in gpio.c seems to be not (yet?) implemented

Huh? https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/hardware_gpio/gpio.c#L28

[soundpaint]

And, by the way, since function gpio_set_function() in gpio.c seems to be not (yet?) implemented

Huh? https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/hardware_gpio/gpio.c#L28

Ah, ok, thanks! I was erroneously looking at src/host/hardware_gpio/gpio.c, which reads:

// todo weak or replace? probably weak
void gpio_set_function(uint gpio, enum gpio_function fn) {

}

Sorry for that one! :-)

[lurch]

Ah, ok, thanks! I was erroneously looking at src/host/hardware_gpio/gpio.c, which reads:

It's generally worth ignoring anything in src/host/ as that's used for building binaries that run on your PC, rather than on the RP2040.

[lurch]

Thanks for the nudge Graham.
I've now chased this up, and been told "0x1f is the official NULL value" and "anything which isn't 0x1f or in the function table is reserved for future use" so I'll make the necessary changes / PRs 🙂

[lurch]

I've reviewed the RP2040 datasheet and the other PDF documentation, and AFAICT there's nothing there that needs changing, it's only pico-sdk that needs updating.

[lurch]

You can close this now @kilograham

[kilograham]

ah, worth putting fixes #xxx in the PR desciption

[lurch]

ah, worth putting fixes #xxx in the PR desciption

I did 😜

GitHub seems to be going a bit wonky round the edges lately? 😕