Skip to content

README.md

Latest commit

 

History

History
executable file
·
166 lines (128 loc) · 6.07 KB

README.md

File metadata and controls

executable file
·
166 lines (128 loc) · 6.07 KB

SENTToUSB — STM32F042 USB ↔ SENT Bridge

USB CDC (Virtual COM Port) adapter for SAE J2716 SENT sensors. Talks to the host using the SLCAN text protocol over any serial terminal. Project is using https://github.com/ucandevices/open-sent-c for SENT implementation.

Hardware
MCU STM32F042G4UX (UFQFPN28, 48 MHz HSI48, no crystal)
PA2 SENT RX — TIM2 CH3 input capture, internal pull-up
PA4 SENT TX — GPIO push-pull driven by TIM14
USB Full-speed CDC (Virtual COM Port, no driver needed on Win10+)

How RX works

Sensor ──SENT signal──► PA2 (TIM2 CH3, RISING edge capture)
                              │
                    ISR: timestamp stored in RX HAL ring buffer
                              │
                    Main loop: bridge decodes batch of 10 edges
                              │
                    SLCAN 't' frame → USB → host
  1. Host sends O\r — bridge enters RX mode.
  2. Every RISING edge on PA2 triggers the TIM2 CH3 capture ISR, which records the raw 16-bit counter value. A separate overflow ISR extends timestamps across the 16-bit rollover (~1.4 ms at 48 MHz).
  3. SentApp_Process() (main loop) polls the RX HAL for complete batches of 10 edges: sync + status + 6 data nibbles + CRC + leading edge of next interval.
  4. The bridge converts timestamps to µs intervals, extracts nibbles, validates CRC, and produces a CAN frame.
  5. The frame is serialised as t<ID><DLC><data>\r and flushed to USB.

Default config (MLX90377): 3 µs/tick, 6 nibbles, DATA_ONLY CRC, seed 0x03, output CAN ID 0x510.

How TX works

Host ──SLCAN 't' frame──► USB CDC RX callback (ISR context)
                              │
                    bridge → TX HAL queue
                    tim14_kick(): start TIM14 if idle
                              │
              TIM14 ISR fires once per half-interval (3 µs/tick):
                Phase 0: pop next interval → PA4 LOW for 15 µs
                Phase 1: PA4 HIGH for remaining ticks
                Repeat until queue empty → PA4 idle HIGH, TIM14 stops
  • TIM14 is reprogrammed on each TX kick: PSC = 0, ARR = (48 MHz × tick_us) − 1. Default 1 tick = 3 µs; the host can change the TX tick period at runtime (see SLCAN SET_TX_TICK below).
  • Each SENT interval = low_ticks active-LOW pulse (5 ticks, SAE J2716 minimum) + HIGH for (N − 5) ticks.
  • The bridge builds the full interval sequence (sync 56T + status + nibbles + CRC + 12T pause) and pushes it to the TX HAL. The ISR drains it without any main-loop involvement.

Switch to TX mode and send one frame:

O\r                       open SLCAN channel
t600102\r                 start TX mode
t52050100123456\r         transmit: status=1, nibbles [1,2,3,4,5,6]

SLCAN quick reference

Command Effect
O\r Open — start SENT RX
C\r Close — stop
V\r / v\r Hardware / firmware version
N\r Serial number (unique per MCU, XOR-fold of 96-bit UID)
F\r Status flags
t<ID><DLC><data>\r Send CAN frame

Control frames (CAN ID 0x600):

data[0] DLC Action
01 1 Start RX
02 1 Start TX
03 1 Stop
04 1 Learn tick period / nibble count / CRC mode from live signal
05 3 Set TX tick period: data[1..2] = tick_x10_us (little-endian, 0.1 µs units; valid range 20–900, i.e. 2.0–90.0 µs)

Example — set TX tick to 5.0 µs (tick_x10_us = 50 = 0x0032):

t60030532 00\r  →  t6003053200\r

TX data frame (CAN ID 0x520):

t52050100123456\r
      ↑↑ ↑
      ││ └─ status byte then data nibbles packed (status=0x01, nibbles=0x00,0x12,0x34,0x56)
      │└─── DLC = 5
      └──── CAN ID 0x520

Decoded RX frame (device → host, default CAN ID 0x510):

t5103AABBCC\r    DLC=3, 3 bytes = 6 nibbles packed high-nibble-first

Python scripts

Script Purpose
sent_viewer.py General SLCAN monitor GUI with TX panel and Learn mode
sent_test.py CLI — open port, apply config, print received frames for N seconds
check_rx.py Loopback sanity check: pings COM8 (TX), listens on COM9 (RX)
tx_signal.py Continuous TX every 10 ms for logic-analyzer capture on PA4
verify_sent.py Logic2 automation: capture PA4 signal and cross-check with USB output

Requirements

pip install pyserial

verify_sent.py additionally needs pip install saleae and Logic2 running with the automation API enabled (port 10430).

Build

STM32CubeIDE manages the Makefile. To build from the command line, set the paths to the bundled tools and run make inside the Debug folder:

set MAKE=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.make.win32_2.2.0.202409170845\tools\bin\make.exe
set GCC=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.gnu-tools-for-stm32.13.3.rel1.win32_1.0.0.202411081344\tools\bin
set PATH=%GCC%;%PATH%
cd Debug
%MAKE% -j4 all

Output: Debug/SENTToUSB.elf (~28 KB flash, ~6 KB RAM on STM32F042G4 with 32 KB flash / 6 KB SRAM).

Flash

SWD (ST-Link)

set CLI=C:\ST\STM32CubeIDE_1.19.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.cubeprogrammer.win32_2.2.200.202503041107\tools\bin\STM32_Programmer_CLI.exe
%CLI% -c port=SWD freq=4000 -w Debug/SENTToUSB.elf -v -hardRst

USB DFU (no ST-Link required)

Step 1 — trigger DFU from the running device (replace COM8 with your port):

python -c "import serial,time; s=serial.Serial('COM8',115200,timeout=1); s.write(b'boot\r'); time.sleep(0.3); s.close()"

Step 2 — flash (~3 s after step 1, once the device enumerates as DFU):

%CLI% -c port=USB1 -w Debug/SENTToUSB.elf -v -hardRst

The boot command writes a magic value (0xDEADBEEF) to a .noinit RAM variable and resets. On the next boot the firmware detects the magic, clears it, and jumps to the STM32F042 ROM bootloader at 0x1FFFC400.