Raspberry Pi Forums

I am working with the compute module and I want to add a Parallel RGB screen using DPI (GPIO's 0-27) and a wifi module using SDIO. The problem is that as far as I know there are only two SD ports specifically SD0 (GPIO's 46-53) which is already used by the NAND flash and SD1 (GPIO's 22-27) which is already used by the RGB screen. I thought I was at a loss until I remembered the Raspberry Pi 3 has an SD card slot on SD0, a WIFI/BT chip using SDIO and allows users access to GPIO's 22-27. How is this possible?

I assume there is another set of pin muxing options that allow SD1 to be used on a different set of pins. This would be great for my project if I could figure out which I can use. Is there a current Alternative Functions table was available OR a current schematic of the RPi 3 with the BCM43438 connections labeled was available OR the device tree for the raspberry pi 3 had information about the pins used for the BCM43438 pin muxing options available?

balornt wrote:I thought I was at a loss until I remembered the Raspberry Pi 3 has an SD card slot on SD0, a WIFI/BT chip using SDIO and allows users access to GPIO's 22-27. How is this possible?

Looking at the devicetree blob for the Pi 3, I can see that the SDIO pins are mapped to GPIOs 34-39 in ALT-3 mode.

It would appear that I was looking at the wrong device tree entries. I was looking at linux/arch/arm64/boot/dts/broadcom/bcm2837-rpi-3-b.dts which is not the correct one. The correct one is linux/arch/arm/boot/dts/bcm2710-rpi-3-b.dts for the raspberry pi 3. How should I have known which one the raspberry pi uses? I know config.txt allows you to specify a different device tree, but how would I know which is the default short of looking at the /boot directory on an actual device? I don't have a RPi 3 so that wasn't an option for me.

balornt wrote:how would I know which is the default short of looking at the /boot directory on an actual device? I don't have a RPi 3 so that wasn't an option for me.

I do have a Pi 3B (two, in fact), but neither were powered up at the time. I looked in the /boot directory of a Pi 2B to see what was there and used fdtdump bcm2710-rpi-3-b.dtb to read the file in there. (As all models of Pi use the same Raspbian (or other) image, they all have the set of device tree files for each Pi).

Secondly how do I know which pins are which? I know those pins are for SD1, but I don't know which is CLK, CMD, and Data0-3.

For this I would have to guess that the pin configuration is in the same order as the ALT3 GPIOs 22-27, as most of the other alternate pin mappings tend to use the same order as each other. Presumably if the mapping was in a different order the pins would need to be listed differently in the dtb