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exp-bminator2

Experimental code for the 2nd generation (simplified) BMInator: an stm32l43x reads a BMI088 and a BME280 over SPI and writes the IMU and baro data out over USART.

The full interface description is documented in the ICD

STM32L431kx UFQFPN32 Pin Assignments:

Pin Function DIR Electrical Connected to
PA0 CK_IN in (reserved for 8Mhz external clock source)
PA1 EXTINT A1 in PullUp bmi088 INT1 (Accel) open drain/active low
PA2 USART2 TX out AF_PP 50MHz debug serial/ boot0 loader console RX
PA3 USART2 RX in PullUp debug serial/ boot0 loader console TX
PA4 ADC1 IN9 in Analog Input Heater Thermistor input
PA5 GPIO PA5 out OUT_PP 2MHz Heater 24V Enable
PA6 ADC1 IN11 in Analog Input Heater current sense
PA7
PA8
PA9 USART1 TX out AF_PP 50MHz host serial input
PA10 USART1 RX in PullUp (5V tolerant) host serial output
PA11 EXTINT A11 in PullUp bmi088 INT3 (Gyro) open drain/active low
PA12 (reserved for CAN TX)
PA13 JTMS/SWDIO debug SWD connector
PA14 JTCK/SWCLK debug SWD connector
PA15 TIM2 CH1 in Input (5V tolerant) host reference time pulse
PB0 GPIO B0 out OUT_PP 2MHz bmi088 CSB2 (Gyro) active low
PB1 GPIO B1 out OUT_PP 2MHz bmi088 CSB1 (Accel) active low
PB2 (not exposed on 32-pin package)
PB3 SPI1 SCK out AF_PP 50MHz SPI sck
PB4 SPI1 MISO in PullUp SPI miso
PB5 SPI1 MOSI out AF_PP 50MHz SPI mosi
PB6 GPIO B6 out OUT_PP 2MHz bme280 CSB (Humid) active low
PB7

If desired, PA0/CK_IN can be used as an external clock source 4..48MHz, see RMA0394 Section 6.1.1 p.182 'External Clock (HSE Bypass)'

The SPI1 bus connects SCK, MISO, MOSI to the BMI088 and BME280. They each require their own separate CSB (active low).

TODO(lvd): early ddln version has PA3 bmi088 INT3 .

DMA Mappings

Device DMA Ch Function
SPI1 RX 1 2 Read spi devices
SPI1 TX 1 3 Write spi devices
USART1 TX 2 6 Serial Output
USART1 RX 2 7 Serial Input
USART2 TX 1 7 Serial Output
USART2 RX 1 6 Serial Input

Connectors

Debug: USART2TX, SWDIO, SWCLK, nRST, GND, 3V3 Host: USART1TX, USART1RX, PA15_TIMEPULSE, Power, GND Heater: Thermistor, GND, Heater10W+, Heater10W-

Requirements

  • BMI088 Self test and configuration check.
  • BMI088 Sample Gyroscope at 2Khz, 250 deg/s full scale
  • BMI088 Sample Accelerometer at 1600Hz, 3G full scale
  • BMI088 Sample internal temperature at 1Hz
  • BME280 Sample environmental temperature, pressure, humidity at 1Hz
  • Watchdog monitors packets streaming regularily
  • Timepulse Sampled
  • Heater power supply, control algorithm based on thermistor input and current sense.
  • Heater state sampled at 8Hz
  • Samples reported over serial port cf ICD
  • Accept commands over serial port
  • Get/set BMI088, BME280
  • Firmware upgradeable atomically (through write command)
  • Send debug information in messages
  • Box averaged gyroscope and accelerometer data output with temperature, ID and debug information on UART2
  • Support multiplexing on UART2

implementation:

  • boot, clock, gpio, debug console for STM32L43x
  • SPI driver using DMA
  • USART driver using DMA
  • ADC driver

debug tools:

  • decoder
  • commander

calibration tool:

  • [] data recorder with multiplexed UART support

TODO(lvd)

  • convert temperatures to correct units, check/fix stm temperature conversion
  • make BMx registers all read only, make special registers to set accel/gyro sample rate and range
  • test command flow more
  • time queue latencies
  • implement stacktrace and assert for cortexm4

Implementation

The code is based on a standalone bare metal environment with no dependencies on third party code. The basic design is that of interrupt handlers pushing data into queues which are handled by the main loop.

A guide to the source code is here.

Debugging

the console can be displayed with

reset; (stty 115200 raw && cat) < /dev/cu.usbmodem1103

and looks like:

SWREV:20629261
CPUID:410fc241
IDCODE:10016435.
DEVID:20333937:48345016:003f0043
RESET:04 PIN
PPLSRC: MSI
cal ts 1037 1378 vref 1661
BMI088 Accel enabled.
Starting gyro self test.
Detected BMI088
Starting accel self test.
neutral xyz: 63 394 1278
positive xyz: 11621 12865 13250
negative xyz: -13285 -11659 -9329
Gyro self test OK.
BMI08x self test completed with 0 errors.
T: 28202 26302 50
P: 37156 -10744 3024 7987 39 -7 9900 -10230 4285
H: 75 369 0 302 50 30
395595 mainloop start

after which a periodic report looks like:

uptime 21.396482  Vdd 3729 mV
enqueued spiq:    77389 evq:      85 cmdq:  0 outq:    79036
dropped  spiq:        0 evq:       0 cmdq:  0 outq:        0
spi1   err tx:        0  rx:       0
usart1 err tx:        0  rx:       0
------------- count - period - cumul - max
        IDLE  14986       66  960088   288
        WAIT
        MAIN   3688      271   39894  1100
      REPORT      1   999997    1088  1088
      ADCIRQ     32    31249      32     8
   USART1IRQ   5886      169    3798     4
 USART1TXDMA   3764      265    2235     4
 USART1RXDMA
     SHUTTER
     GYROIRQ   2038      490    6309     4
    ACCELIRQ   1644      608    5185     4
     8HZTICK      8   124999      10     2
    SPIRXDMA   3684      271    6701     3
    spiq_deq   3683      271  132143  1294
   spiq_xmit   3684      271  100780    51

cmdbuf[18] 05 05 05 05 fc fc fc fc 00 00 00 10 23 00 01 00 e9 00
CMDRX read 16 bytes at address 23000100

The period, cumulative and maximum times are in microseconds. The cumulative time must be divided by the count to get the average time spent. The spiq_xmit and spiq_deq timers measure the time spent between the enqueueing irq and the time the SPI transaction is done, resp dequeued in the main loop. The IDLE and MAIN counters should add up to 1M microseconds per second, the REPORT until SPIRXDMA all run during the IDLE time, the WAIT runs during the MAIN timer.

The tools/ subdirectory contains two self contained Go programs, one that can read a serial stream on stdin and prints a readable format on stdout, and one that can produce messages to set/get registers.

Sample usage:

(stty 921600 raw && cat) < /dev/ttyXXX | go run tools/decoder.go -m
go run tools/encode.go -- register [value] > /dev/ttyXXX

output:

4m20.000127625s
8003    1 451.646390            ID0: [33958182 540227895]
8004    1 451.771390            ID1: [1211387926 4128835]
8020    1 451.396417           BARO: [24968 97725634]
8021    1 451.396417          HUMID: [277121 0]
8022    1 451.396392           TEMP: [63431 23500]
8032 1625 452.116991       ACCEL_3G: [0.049 0.282 0.958]
8039 2018 452.117417  GYRO_250DEG_S: [0.519 -4.227 -2.136]
2023/12/09 14:14:29 Command response[32]: tag:0x17 status:0x00
2023/12/09 14:14:29     data[0x00000010]: 00 0f 22 4a ff e2 00 34 fe 08 00 80 00 00 00 81

Heater logic

Final tuning of the function will be done after tests, but the function to be implemented will have this format (Tth = temperature measured by the thermistor):

For Tth ≤ X° C → P = 10 W (maximum power)
For Tth > X° C → P(Tth) = -m*Tth + n (linear function where power decreases when Tth increases).

X = temperature to be determined iaw the requirement of avoiding icing conditions m, n = parameters of the linear power function in relation to the measured temperature. Ideally the function will reach P = 0 W when moisture is deemed to be no longer present based on the measured temperature (some margins are to be considered).

References

STM Reference documents:

  • PM0214 Programming manual STM32 Cortex®-M4 MCUs and MPUs programming manual
  • RM0394 Reference manual STM32L41xxx/42xxx/43xxx/44xxx/45xxx/46xxx advanced Arm®-based 32-bit MCUs
  • DS11451 STM32L432Kx Ultra-low-power Arm® Cortex®-M4 32-bit MCU+FPU, 100DMIPS, up to 256KB Flash, 64KB SRAM, USB FS, analog, audio
  • DS11453 STM32L431xx Ultra-low-power Arm® Cortex®-M4 32-bit MCU+FPU, 100DMIPS, up to 256KB Flash, 64KB SRAM, analog, audio

Bosch reference documents: