Posts: 9
Joined: Tue Mar 06, 2018 6:16 pm

CM3 console [Solved]

Tue Mar 06, 2018 6:59 pm

Hi all, I am trying to do something that I believe is very basic. In fact I was under the impression that this would work "out of the box," and it is likely that I am just missing something simple, but I can't for the life of me figure out what it is!

I am trying to log in to my CM3 running the latest raspbian stretch-lite image (found here: ) through the UART. My understanding is that UART0 is the more powerful one as it is not tied to the core clock, and for now this would be the better choice, but I can't seem to get either to work.

I have followed some guides for this including ... al-console however, most resources I have been able to find have been targeted towards the RPi3 which I understand occupies the UART0 with its BT module so the process is a bit different.

Here is exactly what I have done using Raspberry Pi Compute Module 3 version 1.0, Compute Module IO Board V3.0:
  • followed these instructions to flash the emmc with the latest raspbian stretch image: ...
  • added "enable_uart=1" to /boot/config.txt (to my knowledge, this step is the same as enabling serial console in raspi-config)
  • verified that /boot/cmdline.txt includes the following phrase: "console=ttyS0,115200"
  • Connected my host machine to a ftdi breakout board configured to use 3.3v logic:
  • Connected RXI from ftdi board to the pin labelled 14 on the CMIO board
  • Connected TXO from ftdi board to pin labelled 15 on the CMIO board
  • Connected GND from ftdi board to a GND pin on the CMIO board
  • booted the cm3 with the USB SLAVE BOOT jumpered to the disabled position
  • ran sudo screen /dev/ttyUSB0 115200 on my host machine and hit enter.
and then...nothing. No output from screen at all.

I have been trying to solve this issue on my own with the following attempted solutions:
  • verified with scope that ftdi board works properly
  • flip tx and rx pins
  • use pins 32 and 33 instead of 14 and 15
  • replace "enable_uart=1" with "dtoverlay=uart1" and "core-freq=250"
  • logging in locally and running raspi-config to turn serial console on
  • recompiled the linux kernel and device tree modules following the instructions found here: ...
  • replacing "enable_uart=1" with "dtoverlay=uart0"

Does anybody have any ideas? Am I missing something crucial here? I am not super familiar with linux so I wouldn't be surprised if I was. Could I be misinterpreting how screen is supposed to work or what the "serial console" means entirely?

Any help is much appreciated.

Last edited by link2cory on Wed Mar 14, 2018 9:48 pm, edited 1 time in total.

Posts: 347
Joined: Fri Jan 01, 2016 10:27 pm

Re: CM3 console

Wed Mar 07, 2018 11:48 pm

Is the CM3 booting?
Can you see the activity light flashing?

Posts: 9
Joined: Tue Mar 06, 2018 6:16 pm

Re: CM3 console

Fri Mar 09, 2018 3:51 pm

The CM3 is booting properly. I have logged into it locally using a keyboard and HDMI cable. Thanks for the suggestion though. Everything helps!

Posts: 9
Joined: Tue Mar 06, 2018 6:16 pm

Re: CM3 console

Fri Mar 09, 2018 4:07 pm


I have switched to the CM3-Lite so that I can swap an SD card between my pi3 and the CM3.

Still no luck UARTing into the CM3 but I have successfully logged in via UART to the pi3 using the same (fresh Raspbian-Stretch-Lite) image.

Posts: 9
Joined: Tue Mar 06, 2018 6:16 pm

Re: CM3 console

Wed Mar 14, 2018 6:17 pm


I was missing jumpers on J3 of the CMIO board to power the gpio banks, so they were dead in the water. Discovered this when I tried setting a pin high with raspi-gpio and not seeing it actually go high.

Posts: 10
Joined: Fri Oct 05, 2018 4:17 am

Re: CM3 console [Solved]

Fri Oct 05, 2018 4:24 am

Even, I am trying to hit the Serial Consol logs for Raspberry CM3 and found your post has a success, could you please post the picture of CMIO J3 Connect for letting the GPIO takes power and make the Serial logs spitting out on the console. That would be the great help for the starters. or even any reference pictures of J3 connections on CMIO.
thank you


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