Smoothieware-CHMT

Smoothieware firmware for the Charmhigh CHM-T36VA, CHM-T48VB, and equivalent pick-and-place machines. Runs on the stock STM32F407 control board.

Originally ported to STM32 by mattthebaker, then extended for OpenPnP by c-riegel based on design input from markmaker (advanced motion, feed rate tuning, 7-axis peeler support), and further developed by janm012012 (DMA serial, drag pin PWM, smart sensing, camera lighting). Encoder feedback is being added by c-riegel.

Precompiled firmware is available in the STM32F407xG folder. To flash the mainboard, a full chip erase is required. While flashing, the vacuum pump and blower may run at full power due to the MCU outputs being in an undefined state. No official schematics are available for these machines, and this firmware is provided as-is with no warranty. Flash at your own risk. Always back up your existing firmware before flashing.

Attention

This firmware has not yet been tested on the CHM-T48VB (RS422 serial). If you have test results, please report them. The last known good commit is f306fb.

Building

Toolchain

Install the ARM GCC toolchain. On macOS:

brew install --cask gcc-arm-embedded

On Debian/Ubuntu:

sudo apt install gcc-arm-none-eabi

Then symlink the toolchain into the project root so the build system finds it:

ln -s $(dirname $(dirname $(which arm-none-eabi-gcc))) gcc-arm-none-eabi

Tested with GCC 15.2 (arm-none-eabi-gcc). The build system includes compatibility patches for this version (older Smoothieware forks may not build with GCC 15+).

Compiling

From the project root:

make clean
make all

The build targets STM32F407xG. Config is compiled into the binary via src/config.default.

Flashing via SWD

Back up existing firmware before flashing:

st-flash read firmware-backup-$(date +%Y%m%d).bin 0x08000000 0x80000

st-flash v1.8.0 + ST-Link V3: required binary padding

st-flash v1.8.0 has a bug when used with ST-Link V3 programmers: the flash loader it uploads to SRAM crashes (CFSR 0x10000 / UNDEFINSTR) when writing binaries smaller than the full 512KB flash. The workaround is to pad the binary to exactly 524,288 bytes with 0xFF (erased flash) before flashing:

#!/usr/bin/env python3
# pad-firmware.py — pad main.bin to 512KB for st-flash + ST-Link V3
import sys
with open(sys.argv[1], 'rb') as f:
    data = f.read()
padded = data + b'\xff' * (524288 - len(data))
outfile = sys.argv[1].replace('.bin', '-padded.bin')
with open(outfile, 'wb') as f:
    f.write(padded)
print(f'{sys.argv[1]}: {len(data)} bytes -> {outfile}: {len(padded)} bytes')

python3 tools/pad-firmware.py STM32F407xG/main.bin
st-flash write STM32F407xG/main-padded.bin 0x08000000

Or use the Makefile targets which handle padding automatically:

make stm32-flash    # pad + flash in one step
make stm32-backup   # read current firmware from MCU
make stm32-verify   # read back and print md5sum

If the first write attempt fails with a flash loader error, retry immediately — the second attempt clears the MCU's fault registers and usually succeeds.

This padding is not needed when flashing with STM32CubeProgrammer or with ST-Link V2 programmers.

Safety notes

While flashing, the MCU outputs enter an undefined state and GPIOs float. On the CHM-T48VB this causes the vacuum pump, blower, and other peripherals to run at full power. This is expected and harmless. Power cycle the machine immediately after flashing completes to restore normal operation.

Always verify the flashed firmware by reading it back and comparing checksums:

st-flash read verify.bin 0x08000000 0x80000
md5sum verify.bin firmware-backup-*.bin

Note: MRI (gdb over serial) is not supported on STM32. Use SWD/JTAG for debugging.

Serial Configuration

Both the CHM-T36VA and CHM-T48VB share the same control board with minor differences:

Machine	Interface	Max Baud (stock)	Transceiver
CHM-T36VA	RS232	115200	U32 (RS232 level shifter)
CHM-T48VB	RS422	460800	RS422 driver

rts_cts_handshake setting

Value	Description
0	Default: no hardware flow control. Both USART1 (RS232) and USART2 (RS422) active. Use this for stock boards.
1	Vespamans modified 48VB: USART1 with RTS/CTS on PA_12/PA_11.
2	janm's 36VA: USART1 with RTS via PD_5 (TX on second RS232 connector).

For stock boards, set rts_cts_handshake to 0 and uart0.baud_rate to 115200. The baud rate applies to both serial ports.

Serial uses DMA for both TX and RX, with a 512-byte circular RX buffer. The RS422 transceiver is enabled at startup via PC_1.

Hardware Flow Control Modifications

To achieve higher throughput (up to 4Mbit) with hardware RTS/CTS flow control, board modifications are required. Both machine variants share the same general approach:

CHM-T48VB

• Add a 1+1 channel isolator chip to unpopulated position U28 (e.g., ADUM121N0BRZ-RL7). Place kapton tape on pads 2 & 3 — these connect to RTS/CTS wires, not board pads.
• Pull two wires from unpopulated U18 pin 4 & 1 (SO8, RS485 transceiver) to pin 2 & 3 of the new isolator chip.
• Bridge the RX/TX/RTS/CTS path at U32 (RS232 level shifter position) with wires for direct logic-level signaling.
• Add a 4-pole through-hole JST connector (or Yeonho SMW250/SMH250).
• Move the 0R resistor from R132 to R131 to route RX from the RS232 input.
• Optionally remove ESD protection components near connectors (required for multi-Mbit speeds).

CHM-T36VA

• Disconnect pin 2 & 3 on U28 from board pads.
• Pull two wires from unpopulated U18 pin 4 & 1 to pin 2 & 3 of U28.
• Remove U32 and connect 4 wires in its place.
• Optionally remove ESD protection components.

USB-Serial Adapter

Keep the adapter as close to the control board as possible. Adapters based on the XR21B1420 chipset have the lowest latency (tested on Linux). The adapter must supply the isolator voltage (e.g., 3.3V).

With RTS/CTS enabled, set OpenPnP to RTS/CTS flow control and disable "Confirmation Flow Control."

Machine Commands

Standard G-codes

Code	Description
G0 / G1	Linear move with feed rate (F) parameter
G28	Home all axes
G92	Set position
M114	Report current position
M115	Firmware identification (used by OpenPnP auto-detection)
M204 Snnn	Set acceleration (mm/s^2)
M205 Xnnn	Set junction deviation
M400	Wait for moves to complete
M999	Reset from halt state

Vacuum and Pneumatics

Code	Description
M808 Snnn	Vacuum pump PWM (16kHz, S = percent)
M810 Snnn	Blower PWM (16kHz, S = percent)

Drag Pin

Code	Description
M816	Drag pin activate. Without S argument: firmware manages PWM automatically to prevent coil overheating. With S nnn: manual PWM override (you must manage current yourself).
M817	Drag pin release. Returns error and enters HALT if pin does not retract after timeout. Requires COMMAND_ERROR_REGEX set to ^.*(error|!!).* in OpenPnP.
M119.1	Read drag pin status. Returns ok0 or ok1. Requires ACTUATOR_READ_REGEX of ^ok(?<Value>\d).

Anti-Stiction Wiggle (ASW): if the drag pin gets stuck, the firmware automatically wiggles X/Y to free it. Enable by adding switch.dragpin.dragpin true to config.default. ASW status is reported in the ok response when engaged.

Camera and Lighting

Code	Description
M820	Buzzer on
M821	Buzzer off
M822 Snnn	Down-looking camera lighting PWM (16kHz, S = percent, via OT2)

Encoder (X/Y Axis Feedback)

The X and Y axes have quadrature encoders connected to STM32 hardware encoder timers. When enabled, the encoder module provides position feedback independent of stepper step counting.

Pin	Function	Timer
PA_15	X encoder channel A	TIM2 CH1
PB_3	X encoder channel B	TIM2 CH2
PA_0	Y encoder channel A	TIM5 CH1
PA_1	Y encoder channel B	TIM5 CH2

TIM2 and TIM5 run in hardware encoder mode with 4x resolution (counting on both edges of both channels) and maximum input filtering for noise rejection.

Encoder Configuration

Add to config.default:

encoder_enable                true
encoder_x_counts_per_mm       0        # set via M923 or M924 after calibration
encoder_y_counts_per_mm       0        # set via M923 or M924 after calibration

When both encoder_x_counts_per_mm and encoder_y_counts_per_mm are non-zero, encoder-driven position control is active. In this mode, the encoder is the position authority: G0/G1 moves use hardware Output Compare interrupts on TIM2/TIM5 to stop the motor when the encoder reaches the target position. The stepper keeps stepping until the encoder says it has arrived, making lost steps irrelevant — the motor simply takes slightly longer to reach the target.

M919 establishes the encoder-to-position mapping. After homing, send M919 X0 Y0 to zero the encoders at the home position.

Move Timeout Safety

When encoder-driven position control is active, each armed move has a timeout: 2 seconds plus 2 seconds per mm of travel distance. If the encoder does not reach the target within this window, the firmware stops the motor and enters HALT. This catches mechanical jams, encoder failures, and stalls without requiring additional hardware. The machine can be recovered with M999.

Segment Buffering (M920)

For S-curve motion with OpenPnP's Simulated3rdOrderControl, a single point-to-point move is broken into ~32 small constant-acceleration segments. Without buffering, the tiny jerk-phase segments execute faster than serial can deliver the next one, causing motion starvation.

M920 S32 tells the firmware to hold the next 32 G0/G1 moves in the Conveyor queue before executing any of them. Each G0/G1 is processed normally by the planner (creating a Block with its own acceleration profile) and its encoder target is stored in a segment buffer. After all segments arrive, the queue is released and execution begins. The OC ISR chains through segments: when both axes reach their targets for segment N, the ISR stops the motors (triggering a block transition in StepTicker, which loads the next Block's speed profile) and arms segment N+1's encoder targets. The last segment stops the motors and exits segment mode.

Machines that do not support M920 simply ignore it, and the G0 commands execute normally.

Encoder M-codes

Code	Parameters	Description
M918		Report encoder positions. Response: ok EX:<count> EY:<count>
M919	Xnnn Ynnn	Set encoder counters and establish position reference (e.g., M919 X0 Y0 to zero after homing)
M921		Report stepper step counts. Response: ok SX:<count> SY:<count>
M922	Xnnn Ynnn	Set stepper step counts. Returns error if machine is moving.
M923	Xnnn Ynnn	Set encoder counts per mm (signed: sign captures encoder polarity). Reports current values if called without parameters.
M920	Snnn	Buffer the next S motion segments before executing. Holds the Conveyor queue until all segments arrive, then releases for chained execution with encoder OC targets. Max 128 segments.
M924	Dnnn	Auto-calibrate encoder counts per mm. Default distance: min(alpha_max_travel, beta_max_travel) / 2. Optional D parameter overrides calibration distance. Must be homed first.

Encoder Calibration

After homing, run M924 to auto-calibrate. The machine moves slowly toward the origin (front-left), measures encoder counts over the travel distance, and calculates signed counts per mm for both axes (the sign captures encoder polarity). Alternatively, calibrate manually:

1. Home the machine (G28)
2. Zero encoders: M919 X0 Y0
3. Move a known distance slowly: G0 X-200 Y-200 F500
4. Read encoder counts: M918
5. Calculate: counts_per_mm = |encoder_count| / 200
6. Set: M923 X<value> Y<value>

If the encoder counts go the wrong direction (negative when they should be positive), the encoder polarity needs to be inverted in the firmware.

OpenPnP Integration

This firmware supports M115 for automatic detection by OpenPnP Issues & Solutions.

Recommended OpenPnP serial settings for stock boards:

Setting	Value
Baud rate	115200
Flow control	XON/XOFF
Line ending	LF
POSITION_REPORT_REGEX	^okC:X:(?<X>-?\d+\.\d+)Y:(?<Y>-?\d+\.\d+)Z:(?<Z>-?\d+\.\d+)A:(?<A>-?\d+\.\d+)B:(?<B>-?\d+\.\d+)C:(?<C>-?\d+\.\d)D:(?<D>-?\d+\.\d)
COMMAND_ERROR_REGEX	^.*(error|!!).*

Timer Allocation

Timer	Function
TIM2	X axis encoder (hardware encoder mode)
TIM3	us_ticker (system microsecond timer, extended from 16-bit to 32-bit via overflow ISR)
TIM5	Y axis encoder (hardware encoder mode)
TIM7	Step ticker (100kHz step pulse generation)
TIM14	Unstep timer (one-shot, minimum step pulse width)

Note: us_ticker was moved from TIM2 to TIM3 to free TIM2 for the X axis encoder. TIM3 is 16-bit; an overflow ISR extends the counter to 32-bit with a race-guarded read.

Port Status

All peripherals ported and tested on STM32F407:

• mbed hooks, stm32f4xx libs, timers, watchdog, GPIO, ADC, PWM, build scripts

Machine status:

• Config file: 48VB complete
• Pin map: 48VB/36VA complete
• Operation: all system functions operational
• 7-axis support (PAXIS=7), planner queue size 128

License

Smoothieware is released under the GNU GPL v3.