RP2040/RP2350 stepper motor control example

Bipolar stepper motor direct control example for Raspberry Pico MCU family.

Full step mode (two-phase) or half-stepping with GPIO (SIO).

Microstepping with PWM.

Compatible with Dual H-bridge motor drivers, like DRV8835 or DRV8836.

Coils could be connected directly to the GPIO pins (without a driver or mosfet bridge) if the motor is small enough and could work from 3.3V and 12 mA per coil.

Usage

Vendor-in to your project:

mkdir -p vendor
git submodule add https://github.com/siberex/pico_stepper_direct.git vendor/pico_stepper_direct

Edit your CMakeLists.txt:

# Assuming Pico SDK set up earlier

add_subdirectory(vendor/pico_stepper_direct/src)
target_include_directories(${PROJECT} PRIVATE
        ${CMAKE_CURRENT_LIST_DIR}
        # ...
        vendor/pico_stepper_direct/src
)
target_link_libraries(${PROJECT}
        pico_stdlib
        # ...
        stepper
)

In your code (see also example.cpp):

#include "pico/stdlib.h"
#include "stepper.h"

int main() {
    const Stepper stepper{PIN_A_POSITIVE, PIN_A_NEGATIVE, PIN_B_POSITIVE, PIN_B_NEGATIVE};
    stepper.m_DurationMicroseconds = 5'000;
    const int stepsPerRevolute = 200;
    
    while (true) {   
        stepper.fullStep(stepsPerRevolute);
        stepper.halfStep(-stepsPerRevolute * 2);
        
        stepper.enableMicrostepping();
        stepper.microStep(stepsPerRevolute / 4);
        stepper.disableMicrostepping();
    }
}

Build

Prerequisites: cmake, binutils, Pico SDK 2.1.1

mkdir -p build && cd build
cmake -DPICO_USE_FASTEST_SUPPORTED_CLOCK=1 -DPICO_BOARD=pimoroni_tiny2040 -DCMAKE_BUILD_TYPE=Debug -DPICO_DEOPTIMIZED_DEBUG=1 ..
# To clear CMake cache and reset compile options to defaults:
# cmake --fresh ..
make -j4

Flash by SWD

Prerequisites: openocd

# SWD flash (openocd required):
make flash

# Note: if gdb server is run, use this to flash via telnet interface:
./flash.sh

Reset device programmatically from the host:

# To reset MCU with SWD:
./reset.sh
# To reset MCU via USB connection:
picotool reboot -f

Flash by USB

Prerequisites: picotool

# BOOTSEL flash (picotool required):
make flash_usb

# Flash manually with picotool (`make flash_usb` does exactly this):
TARGET=stepper_direct
picotool load -fx ${TARGET}.uf2

Debug

ℹ️ Note: Use -f target/rp2350.cfg or -f target/rp2350-riscv.cfg for RP2350. ℹ️ Note: Use debug builds for symbol resolution to work: cmake -DCMAKE_BUILD_TYPE=Debug -DPICO_DEOPTIMIZED_DEBUG=1 ..

OpenOCD will start a telnet server (port 4444) and two GDB servers (rp2040.core0: port 3333, rp2040.core1: port 3334):

# Attach to SWD at 10MHz:
openocd -f interface/cmsis-dap.cfg -f target/rp2040.cfg -c "adapter speed 10000"

# Open OCD console:
telnet localhost 4444
> halt
> resume
> reset run
# https://openocd.org/doc/html/General-Commands.html#resetcommand
> reset init

# GDB core0:
TARGET=stepper_direct
gdb "${TARGET}.elf" -ex "target extended-remote localhost:3333"

ℹ️ Note: RP2040’s ARM Cortex-M0 don't have Serial Wire Output (SWO) over SWD. RTT can be used instead.

Segger RTT serial console setup over SWD

This will set up RTT console on 127.0.0.1 port 9090. And gdb server on ports 3333 and 3334.

Connect with CoolTerm, VSCode Serial Monitor, minicom, PuTTY, netcat, telnet or whatever.

In one command:

# With CMake:
make gdb
# With separate script:
./debug.sh
# Or run directly (`make gdb` does exactly this):
# openocd -f interface/cmsis-dap.cfg -f target/rp2040.cfg -c "adapter speed 10000" -c "init; rtt setup 0x20000000 0x42000 \"SEGGER RTT\"; rtt start; rtt server start 9090 0"

rlwrap nc localhost 9090

cd build
TARGET=stepper_direct
# core0:
gdb "${TARGET}.elf" -ex "target extended-remote localhost:3333"
# core1:
gdb "${TARGET}.elf" -ex "target extended-remote localhost:3334"

Set up manually (how it works in detail):

# Verify CMakeLists.txt:
# pico_enable_stdio_rtt(${PROJECT} 1)

# Use the telnet interface to issue RTT-specific commands:
telnet localhost 4444

> halt
# RAM start address: 0x20000000 
# RP2040 SRAM size is 264KB = 0x42000
# RP2350 SRAM size is 520KB = 520 * 1024 = 532480 = 0x82000
> rtt setup 0x20000000 0x42000 "SEGGER RTT"
> rtt start

# Expected output:
# rtt: Searching for control block 'SEGGER RTT'
# rtt: Control block found at 0x20002ab0

# Unexpected output:
# SWD DPIDR 0x0bc12477, DLPIDR 0x00000001
# Failed to read memory at 0x20042000
# rtt: No control block found

# After setup succeed:
> rtt server start 9090 0
# OR, to dump all serial output to file:
#> rtt channelfile 0 rtt_output.txt

# Flash
> program stepper_direct.elf verify reset

# Separate by core:
#> rp2040.core0 rtt setup 0x20000000 0x42000 "SEGGER RTT"
#> rp2040.core0 rtt start
#> rp2040.core0 rtt server start 9090 0
#> rp2040.core1 rtt setup 0x20000000 0x42000 "SEGGER RTT"
#> rp2040.core1 ...

See also: https://kb.segger.com/Raspberry_Pi_RP2040

Other On-Chip Debuggers

probe-rs

# brew install probe-rs/probe-rs/probe-rs
# OR: cargo install probe-rs-tools --locked
probe-rs run --chip RP2040 "${TARGET}.elf"

PyOCD

# python3 -m pip install pyocd
pyocd gdbserver --target rp2040_core0
pyocd rtt
gdb "${TARGET}.elf" -ex "target extended-remote localhost:3333"