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PicoPOST

[!NOTE] You can get a quick summary from the blog post! Introducing the PicoPOST - The Retro Web Blog

Introduction

PicoPOST is a PC diagnostic card for systems with, at least, an 8-bit ISA slot. It's based around the Raspberry Pi Pico, powered by an RP2040.

PicoPOST is designed to provide many additional benefits over the basic POST cards that are commonly available from Chinese vendors on eBay and other sites.

This project is getting ready for public usage, with a few prototypes already in use for development purposes. More information soon as it gets finalized.

Implemented features

• Simple user interface, with a graphical monochrome 128x32 OLED display and a few buttons living on their own remote control
• Port 80h readout, with 4-place output history
• Port 90h readout, for IBM PS/2s
• Port 84h reaodut, for Compaq machines*
• Port 300h readout, for some EISA systems*
• Port 378h readout, for some Olivetti machines*
• More complete bus activity dumping facility
• Reset pulse detection
• +5V and +12V and -12V voltage monitor**
• Display is dimmed after 15s of inactivity to mitigate burn-in
• Flying Toasters! screensaver after 30s of inactivity on the main menu

*: We don't have a specimen handy, so we need confirmation from someone else out there.
**: Negative voltages into a positive ADC is too much mental gymnastics without additional hardware

Videos

We are slowly compiling a YouTube playlist with a whole bunch of demonstration pieces, showing what the PicoPOST is capable of doing.
Stay tuned for more content!

Wishlist

New features have been implemented with the new rev 6 PCB and matching firmware.

• Full bus activity trace (HW OK, FW provisioned, but we need to make sure we are not missing data)
• Bus clock reader (HW OK, FW TBD)
• ... anything else, as long as the hardware allows it and someone implements it in firmware

Building the firmware

Automagically

We make use of Visual Studio Code and the official Raspberry Pi Pico extension for an easier life. When you first open the project in VSCode, you will be prompted to install a few suggested extensions; accept the proposal and follow on-screen instructions.

You should now be greeted by the CMake and Pi Pico sidebar panels. Use the CMake panel to switch between Debug or Release builds, then refer to the Pico panel for building, uploading, and debugging the firmware.

It's already set up to probe for a compatible debugger via OpenOCD and gdbserver, and it works really well with our official Raspberry Pi Debug Probe. I expect other SWD debuggers to work just as well (J-Link, STLink, ...).

Manually

The firmware is built using the official Raspberry Pi RP2040 SDK. Follow the official documentation for setting it up.

The procedure is pretty straight-forward:

1. Clone the repo

   mkdir ~/repo
   cd ~/repo
   git clone https://github.com/TheRetroWeb/PicoPOST

2. Enter the repo and initialize it

   cd PicoPOST
   git submodule init
   git submodule update

3. Prepare the build system with CMake

   export PICO_SDK_PATH /path/to/pico/sdk
   cmake -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE \
       -DCMAKE_BUILD_TYPE:STRING=Release \
       -DCMAKE_C_COMPILER:FILEPATH=/usr/bin/arm-none-eabi-gcc \
       -DCMAKE_CXX_COMPILER:FILEPATH=/usr/bin/arm-none-eabi-g++ \
       -S./firmware \
       -B./build \
       -G "Unix Makefiles"

4. Build the firmware

   cmake --build ./build --config Release --target all -j $(nproc)

Customize the firmware

There are a couple of details you might want to tune at compile time. More specifically, you may want to better calibrate the voltage monitor to show more accurate results.

In the primary firmware\CMakeLists.txt file, there are three variables you can set to skew the final ADC conversion result. These were added to account for resistor tolerances in the voltage divider circuits.

• CALIBADJ_5V, correction factor for the +5V rail
• CALIBADJ_12V, correction factor for the +12V rail

Calculating these factors is pretty straight forward:

• Install the default firmware
• Connect PicoPOST to your computer of choice with a known good power supply
• Enter Voltage Monitor mode
• Turn on the computer
• With a multimeter, measure the rail voltage as close as possible to PicoPOST
• Compute the required calibration factor by dividing the measured value with the one shown by PicoPOST
• Edit the CALIBADJ variable and build the firmware again

Flashing the firmware

1. In order to load new firmware, the Pico must be booted into UF2 mode:
   • If the board is powered off, keep the BOOTSEL button pressed while plugging the USB cable into the Pico itself.
   • If the board is already powered, you can short the "Pico Reset" pins on the back of the card instead of removing the USB cable.
   • Alternatively, if the board is powered via USB from a PC with a data cable, you can move to the Update FW menu entry. By pressing Enter, the Pico will then be rebooted into UF2 mode automatically.
2. A mass storage device should be now mounted on your computer.
3. Drag and drop (or copy and paste) the .uf2 firmware file into the device.
4. Once loaded, it will automatically restart and disconnect.
5. If all went well, you should now be greeted by the main menu on the OLED display.
   You can verify the current firmware version by entering the Info page.

Interested in helping?

• Submit issues and pull requests!
• Join us in the #picopost channel in The Retro Web discord server
• Join us and other developers of retro Pico hardware (such as PicoGUS and PicoMEM) in the Retro Pico Hardware discord server

Directories

datasheets/  Reference documentation for components used in the PicoPOST
firmware/    Source code for the PicoPOST firmware (written in C/C++ with the official Pico SDK)
pcb/         KiCad schematics and PCB design files

License

The firmware portion of PicoPOST is licensed under the MIT license.
The hardware portion of PicoPOST is licensed under the CERN OHL v2 Permissive license.