About the brs-tester

This project implements a tester for DEC flipchips in the B/R/S series. Those modules are used in PDP-8, PDP-8/S, PDP-9 and in PDP-10 with KA processor. This project was created as a part of the restoration os the PDP-9 with serial number 203.

The modules uses 0 and -3V volts for the logical 0 and 1. The tester can detect both logical and electrical failures.

The software runs on a Raspberry Pi with Raspberry Pi OS. It's been tested with Raspberry Pi OS 11/12 on Raspberry Pi 3/4/5.

Electronics

The major parts is:

• Levelshifter boards
• Backplane board with control logic and measurement circuitry
• Power supply
• Load module

Levelshifter boards

There are fifteen boards that takes two pins each and can act as an input/outout levelshifter to 3.3 V TTL levels from 0 and -3 V levels. Every pin can be completely disconnect by a relay. Every pin can also be connected to the measurement bus.

Backplane board

The backplane contains glue logic and a measurement circuit. It also interconnects all signals between the other boards.

Power supply

Makes all voltages needed for the tester.

Load module

The load module can connect different resistors to the measurement bus in order to load test outputs from flipchips.

Software

For the time beeing the software is run from a shell and takes different input parameters. Run brs-tester --help to get help text. When a board is tested i takes a file with test vectors.

At startup a udev rule tiggered on the start of the GPIO subsysten will run a shell script that will export all necessary GPIO pins and run 'brs-tester --init'. This will initialize the tester and put the hardware in a known state.

Using the tester

TBD

Test vectors

There is a template file in the "vectors" folder that tries to explain how it works.

Setting up the Raspberry Pi

In /boot/config.txt Enable I2C, Set I2C clock to 400kHz

dtparam=i2c_arm=on
dtparam=i2c_arm_baudrate=400000

Enable support for ADS1115 ADC:

dtoverlay=ads1115
dtparam=cha_enable
dtparam=chb_enable
dtparam=chc_enable
dtparam=chd_enable

If you want a serial console connected to the pin header on the back:

enable_uart=1

The default speed is 115200 baud, if you want something else, change /boot/cmdline.txt

Install tools for build:

sudo apt install git
sudo apt install autoconf
sudo apt install autoconf-archive

Install libgpiod:

cd ~/
git clone https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git
cd libgpiod
./autogen.sh
make
sudo make install

Get and install the brs-tester (this package),

cd ~/
git clone https://github.com/anders-bzn/brs-tester.git
cd brs-tester
make
sudo make install