An Easy-to-Use RPI Pico PIO Emulator

This is a simple tool for emulating behavior of single state machine (SM) in RPI Pico PIO. The tool is almost independent of OS environment (Linux, Windows etc.) and requires a standard C/C++ compiler only. While the provided emulator cannot handle multi-SM, the whole design flow supports designing multi-SM applications.

日本語での説明はインターフェース誌2022年9月号pp.36-48（紙媒体または電子書籍）にあります． ラズベリーパイPicoの簡単PIOエミュレータです．ステートマシン1つの動作検証専用ですが，多くの場合は 事足りるでしょう．Cコンパイラさえあれば，サンプルを真似するだけですぐに使えます．

1. Overall Design Flow

The provided design flow is shown below. Unlike other similar debugging environments, the source file is not a standard PIO assembler code, i.e, ".pio" code.

(Step 1) Write an assembler code in C language, by calling the provided C functions which correspond to assembler instructions, like PIO coding in Micro Python. A list of the C functions will be shown later in Section 2, and an example code is here.

(Step 2) Compile your source with the provided emulator source (a C header file "picopio_emu.h" ), and you will get a binary executable.

(Step 3) Run the binary with an input vector CSV file. An output trace CSV file and an assembler source (.pio code) for Pico SDK will be generated. You can observe the execution result by free Flow CSV Viewer etc. The assembler source include a C API function for initializing state machine.

(Step 4) Write your Pico application in C and build with the assembler source generated in Step 3. Here is an example.

There are important limitations in this environment, as shown in this table.

2. Preparation of PIO Assembler Code (Important: In C)

Write your assembler code ( sample ) using C functions in the following three tables. The first table is a list of emulator control functions. Call pio_code_start(), pio_code_end() and pio_run_emulation() in this order. A function pio_code_start_simple() is just a simplified version of pio_code_start().

Use these functions to write your assembly code. Each function corresponds to PIO instruction. Assembly code should be located between pio_code_start() and pio_code_end().

The following functions correspond to pseudo instructions.

You can use the following prameters to control emulation input and output. Place these definitions before including picopio_emu.h.

3. Preparation of Input Test Vector

Write an input data as a CSV file (sample) , if your program refers GPIO, IRQ and/or . The meanings of each column are shown below.

4. Emulation and Observation of the Results

Compile your program by conventional C/C++ compilers such as gcc and Visual Studio. Then simply run the program.

Two output files will be generated. One is an execution trace file (sample) . The file is in CSV format and each columns are defined below. Another is a ".pio" file (assembler source) for building Pico executable binary.

While the generated CSV is readable, it will be better to use a free waveform viewer such as Flow CSV Viewer.

5. Preparation of Pico ARM Code in C

The generated ".pio" file include a C API function Assembler_Function_Name_config() (here is an example of the API function) . Call this function first for initializing state machine in your Pico application code, and then call pio_sm_set_enabled() to run state machines.

Here is another implementation example which demonstrates the use of multiple statemaches and IRQ.

6. Build Binary for Real Hardware

Use a standard Pico C/C++ SDK to build a executable binary from the generated assembly code.

7. Example Codes

7.1 Sample 1

Here is a sample implementation of simple waveform output.

7.2 Sample 2

Here is a sample implementation of multi-SM and IRQ.

8. Support

Any information on bugs is welcome!

バグのお知らせは歓迎です！