sekigon-gonnoc / pio_usb_simulation

Dumping ground for Raspberry Pi Pico Programmable IO simulation of low speed USB

Raspberry Pi Pico Programmable IO Low Speed USB RX Simulation

This repository contains a resources demonstrating simulation of low speed USB reception.

Using the simulator rp2040pio: https://github.com/soundpaint/rp2040pio

With documentation: https://rp2040pio-docs.readthedocs.io/

Files

• FIFODumper.java - Small utility which dumps the PIO RX fifo to a file. You can read the fifo directly in the simulator, but for lager packets I've found having it in a file is useful.
• saleae_logic_csv_to_sim_script.py - Original data was captured with a Saleae Logic analyser and exported to a CSV file. This tool converts it to a simulation script.
  • Line 44 sets the timing, converting seconds to clock cycles. It's currently set at 16 x oversampling given a 1.5Mhz signal.
• usb_packet_saleae.csv - Example capture from a cheap keyboard. Saleae Logic export of D- channel.
• usb_packet.sim - Result of saleae_logic_csv_to_sim_script.py ran against usb_packet_saleae.csv.
• usb_rx.mon - Simulation script, configuring the virtual PIO module and feeding in the simulation data.
• usb_rx.pio - PIO program to run within SM

Usage

1. Clone simulator

   git clone [e-mail]:soundpaint/rp2040pio.git
   

   If using irq wait instruction you may find a bug, see my branch: https://github.com/pgreenland/rp2040pio/tree/irq_wait - should really submit a PR

2. Ensure pre-requisites available, docs list:

   • Java OpenJDK 11.x (other recent versions should also work, but have not been tested)
     • Debian: apt-get install openjdk-11-jdk
   • GNU Make

3. Build rp2040pio

   pushd rp2040pio
   make all
   popd
   

4. Build simple tool to extract and store any data from rx fifo before its overwritten

   javac --source-path "rp2040pio/java" FIFODumper.java
   

5. Assemble PIO program.

   The pioasm binary is built during a pico build, I've previously dug it out of the build directory for a random project which uses pio.

   Seems you can build it directly:

   git clone https://github.com/raspberrypi/pico-sdk.git
   cd pico-sdk/tools/pioasm
   mkdir build
   cd build
   cmake ..
   make
   

   However its acquired, assemble the usb_rx.pio program:

   pioasm -o hex usb_rx.pio usb_rx.hex
   

6. Launch simulation server

   java -jar rp2040pio/jar/rp2040pio_server.jar &
   

7. Launch displays

   java -jar rp2040pio/jar/rp2040pio_gpioobserver.jar &
   java -jar rp2040pio/jar/rp2040pio_codeobserver.jar &
   java -jar rp2040pio/jar/rp2040pio_diagram.jar &
   

8. Launch fifo dumper

   java -Xdiag -classpath "rp2040pio/java:." FIFODumper > fifo.log &
   

9. Launch simulation script in monitor

   java -jar rp2040pio/jar/rp2040pio_monitor.jar -f usb_rx.mon &
   

10. Run simulation

    Either hitting the emulate x cycles button in the "Diagram Creator" window.

    Or launch another monitor instance:

    java -jar rp2040pio/jar/rp2040pio_monitor.jar
    

    And execute a number of cycles:

    trace -c 2000
    

    Having tried both methods, while making these notes, there may be something odd going on. In that the fifo.log file doesn't contain the same contents when "trace -c 2000" is executed. Clicking the emulate button within the "Diagram Creator", with 500 cycle blocks leads to the fifo.log containing the output that Saleae Logic's decoder caculated.

    For reference the included samples should be decoded as:

    • 0x80
    • 0xc3
    • 0x80
    • 0x06
    • 0x00
    • 0x01
    • 0x00
    • 0x00
    • 0x12
    • 0x00
    • 0xe0
    • 0xf4