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CHIP Serial Console

2021-03-03 | #raspberrypi #hack #100daystooffload #openbsd #chip

Intro

Since getting a Pocket C.H.I.P[1], I'm looking for more ways to use it outside the original configuration, and came across a Hackernoon post on using a CHIP as a serial console[2].

1: https://www.ecliptik.com/Pocket-CHIP/ (https://www.ecliptik.com)
2: https://medium.com/hackernoon/turn-your-pocketchip-into-a-badass-on-the-go-hardware-hackers-terminal-84b1edc939f (https://medium.com)

I also wanted to install OpenBSD onto a RaspberryPi 3[3] - unlike most RaspberryPi installs where a sdcard image is flashed and boots up - OpenBSD requires following the full installation procedure[4] on the console. Sure you could hook up it up to HDMI and a USB keyboard, but what's the fun in that? So I took the oppurtunity to do both.

3: https://brainsnapped.com/2020/10/22/openbsd-on-the-raspberry-pi-3-model-b/ (https://brainsnapped.com)
4: https://www.openbsd.org/faq/faq4.html (https://www.openbsd.org)

Hardware

Following the Hackernoon post, and using the RPI GPIO documentation[5], I soldered some lead pins onto the CHIPs `5V`, `GND`, `TXD` and `RXD` breakout at the top, made some basic GPIO wires and hooked it all up. Using the `5V` has the added benefit of powering the RaspberryPi from the CHIP battery, which in makes both of them portable.

5: https://www.raspberrypi.org/documentation/usage/gpio/ (https://www.raspberrypi.org)

C.H.I.P. Serial Console [IMG]

Software

To connect via serial console, first release `/dev/ttyS0` from systemd,

sudo systemctl stop serial-getty@ttyS0

Many articles suggest using minicom[6] as a serial console, but I prefer screen[7], and used it for years when working in datacenters.

6: https://salsa.debian.org/minicom-team/minicom (https://salsa.debian.org)
7: https://www.gnu.org/software/screen/ (https://www.gnu.org)

The OpenBSD console uses a baud rate of `115100` and transmission of eight bits per byte `cs8`. Connecting requires `sudo`, even if your `chip` user is in the `tty` group due to some udev/systemd permissions wonkiness.

sudo screen /dev/ttyS0 115200,cs8

The serial console works well, although occasionally there is missing data, but after remembering how to use the OpenBSD disk partitioner - OpenBSD 6.8 was running on a RaspberryPi 3. Once the installation is complete, if DHCP was setup during install, connecting to it over ssh is trivial and no longer requires the serial console.

Conclusion

While as much fun as this is, it's not nearly as useful as it could have been years ago when troubleshooting misbehaving Sun Netra[8] or Sun Fire[9] systems. For now though it's a good hack, useful in the right circumstances, and just looks cool.

8: https://shrubbery.net/~heas/sun-feh-2_1/Systems/Netra_t1_105/spec.html (https://shrubbery.net)
9: https://shrubbery.net/~heas/sun-feh-2_1/Systems/SunFire280R/SunFire280R.html (https://shrubbery.net)