What is causing IMX7D's emmC SODIMM pin 32 to be at 1 V even if I configured it to output low voltage?

Hello, guys how are you all?

I am facing an issue when trying to operate the SODIMM pin 32 (pin X16.29 on Iris 2.0). When I configure it as a general purpose output, the low voltage level stays at 1 V instead of 0 V yet the high level output is the correct correct 3.3 V. That being said, when I create a 1 kHz square signal with the pin, the high voltage is 3.3 V and the low voltage is 1 V - which can be seen via my scope.

My first guess was something related to the Iris board, so I checked the schematics and observed that SODDIM pin 32 is the UART_B_CTS signal, which is parallel-connected to the X16.29 pin and to the UART transceiver IC. Being UART_B_CTS an output pin of the transceiver (pin 16 of IC6), I thought that maybe the IC output was the cause of such behavior. I unsoldered that pin but had no success on observing a change in the operation scenario.

I also tried forcing a pull-down (via pad configuration in my code) to see if it would cause any type of different behavior but the earlier scenario was sustained.

That being said, my question is: is there anything connected in the Colibri SoM PCB that could cause such behavior? Could you guys please help?

Many thanks!


HW and SW configuration:
Iris 2.0, Colibri IMX7D 1GB emmC
Embedded bare metal code being developed in the M4
Iris pin: X16.29; SODIMM pin: 32; functionality: general purpose output to generate a 1 kHz signal.

Hello, support!

Just to provide further information:
I am able to select the status of the X16.29 pin via Uboot using the gpio clear 181 and gpio set 181. When issuing a gpio clear 181, the output level stays at 1 V. When issuing a gpio set 181, the level goes to 3.3V. When using gpio clear 181 and gpio input 181, I can see via my scope that the voltage level is 1 V and Uboot reads that the voltage is high:

Colibri iMX7 # gpio clear 181
gpio: pin 181 (gpio 181) value is 0 // This voltage level is 1 V via scope
Colibri iMX7 # gpio input 181
gpio: pin 181 (gpio 181) value is 1 // But should not be.

Ps 1: I also tested the GPIO2_26, which is the Iris X16.14 pin. When issuing gpio sets, clears and inputs, everything works properly and signal measurement via scope is adequate.

Many thanks


The X1.32 Colibri iMX7 pin routed directly to iMX7 ball E9 (SAI2_RXD). Nothing else is connected there on the module. Please check a pinmux settings at your M4 code.

Hello, Alex, thank you for your reply!
As I pointed in the update, even when issuing commands via Uboot the low level is 1 V - M4 is not even under operation.

Many thanks

So check a U_Boot pinmux settings.

Thank you, Alex!!