1

I'm beginning bare metal programming on the Pi4. As a simple 'hello world' equivalent I'm trying to get the ACT led to blink. I have seen references that it is tied to the BCM2711 GPIO Controller pin 16. However, looking at the BCM2711 datasheet I can't find any references to this. Is this information available in a datasheet or an official documentation source somewhere?

2
  • it's different on pi3 and pi4 - read the README in boot/overlays folder for some insight - though this won't give you an answer (i.e. it mentions a GPIO expander and a special driver ... Feb 3 at 0:42
  • Good question! Welcome to RPi SE.
    – Seamus
    Feb 5 at 16:14
1

The BCM2711 peripherals documentation can be found on the Foundation website.
https://datasheets.raspberrypi.org/bcm2711/bcm2711-peripherals.pdf

The GPIO is a superset of the earlier GPIO i.e. it is identical EXCEPT some pins have additional modes and the peripheral address differs between models. See https://www.raspberrypi.org/documentation/hardware/raspberrypi/peripheral_addresses.md

AFAIK there is no public documentation for the on-board interfaces e.g. ACT LED.

Exploring the gpiochip implementation in latest Raspberry Pi OS gives some hints about the on-board GPIO functions.

gpioinfo pinctrl-bcm2835

Update: The following may be of interest re the expansion GPIO.

gpioinfo raspberrypi-exp-gpio
gpiochip1 - 8 lines:
    line   0:      "BT_ON"       unused  output  active-high 
    line   1:      "WL_ON"       unused  output  active-high 
    line   2: "PWR_LED_OFF" "led1" output active-low [used]
    line   3: "GLOBAL_RESET" unused output active-high 
    line   4: "VDD_SD_IO_SEL" "vdd-sd-io" output active-high [used]
    line   5:   "CAM_GPIO"       unused  output  active-high 
    line   6:  "SD_PWR_ON" "sd_vcc_reg"  output  active-high [used]
    line   7:    "SD_OC_N"       unused   input  active-high 
3
  • Why would they not include this information in the BCM2711 datasheet? Feb 3 at 10:15
  • @RyanMcClue Because it has nothing to do with the SOC this is the design of the Pi board and the extra hardware they use. Why it is not documented is one of life's mysteries.
    – Milliways
    Feb 3 at 11:38
  • This is a really useful answer!
    – Seamus
    Feb 5 at 16:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.