mpremote doesn't connect on STM32L452CE

[Tico06]

Hi There,

I have a simple board with STM32L452CE and an USB socket. No HSE, one LSE at 32.768Khz. The firmware is uploaded successfully, and once the board is plugged with a USB cable to a PC, the PYBLASH drive pops up with boot.py, main.py, and pybcdc.inf files. Thus I guess no issue with the board itself.

When the user tries to connect to the board with mpremote under Windows with connect auto, it says no board is found. If the COM port is provided, it results in an SerialTimeoutException: Write timeout.

I was suspecting a driver issue under Windows, but now, I think it could be the clocking issue. My config files are inspired from NUCLEO_L452RE.

my mpconfig.h

#define MICROPY_HW_BOARD_NAME       "Barbatruc"
#define MICROPY_HW_MCU_NAME         "STM32L452CE"

#define MICROPY_PY_SOCKET           (0)
#define MICROPY_PY_NETWORK          (0)

#define MICROPY_HW_ENABLE_RTC       (1)
#define MICROPY_HW_ENABLE_RNG       (1)
#define MICROPY_HW_ENABLE_DAC       (1)
#define MICROPY_HW_ENABLE_SERVO     (0) // SERVO requires TIM5 (not on L452).
#define MICROPY_HW_HAS_SWITCH       (1)

// MSI is used and is 4MHz
#define MICROPY_HW_CLK_PLLM (1)
#define MICROPY_HW_CLK_PLLN (40)
#define MICROPY_HW_CLK_PLLP (RCC_PLLP_DIV7)
#define MICROPY_HW_CLK_PLLQ (RCC_PLLQ_DIV2)
#define MICROPY_HW_CLK_PLLR (RCC_PLLR_DIV2)
#define MICROPY_HW_FLASH_LATENCY FLASH_LATENCY_4

// The board has an external 32kHz crystal
#define MICROPY_HW_RTC_USE_LSE      (1)

// UART config
#define MICROPY_HW_UART1_TX     (pin_B6)
#define MICROPY_HW_UART1_RX     (pin_B7)
#define MICROPY_HW_UART2_TX     (pin_A2)    // VCP TX
#define MICROPY_HW_UART2_RX     (pin_A3)    // VCP RX
#define MICROPY_HW_UART3_TX     (pin_C10)
#define MICROPY_HW_UART3_RX     (pin_C11)
#define MICROPY_HW_UART4_TX     (pin_A0)
#define MICROPY_HW_UART4_RX     (pin_A1)
// USART2 is connected to the ST-LINK USB VCP
// #define MICROPY_HW_UART_REPL        PYB_UART_2
// #define MICROPY_HW_UART_REPL_BAUD   115200

// USB config
#define MICROPY_HW_ENABLE_USB       (1)
#define MICROPY_HW_USB_FS           (1)
#define MICROPY_HW_FLASH_FS_LABEL "FSflash"
#define MICROPY_HW_USB_MANUFACTURER_STRING      "Micropython"
#define MICROPY_HW_USB_PRODUCT_FS_STRING        "Virtual Comm Port in FS Mode"
#define MICROPY_HW_USB_CONFIGURATION_FS_STRING  "Board Config"
#define MICROPY_HW_USB_INTERFACE_FS_STRING      "Board Interface"
#define MICROPY_HW_USB_MSC_INQUIRY_PRODUCT_STRING "Board Flash "


// I2C buses
#define MICROPY_HW_I2C1_SCL     (pin_B8)
#define MICROPY_HW_I2C1_SDA     (pin_B9)
#define MICROPY_HW_I2C2_SCL     (pin_B10)
#define MICROPY_HW_I2C2_SDA     (pin_B11)
#define MICROPY_HW_I2C3_SCL     (pin_A7)
#define MICROPY_HW_I2C3_SDA     (pin_B4)
#define MICROPY_HW_I2C4_SCL     (pin_C0)
#define MICROPY_HW_I2C4_SDA     (pin_C1)

// SPI buses
#define MICROPY_HW_SPI1_NSS     (pin_A15)
#define MICROPY_HW_SPI1_SCK     (pin_A5)
#define MICROPY_HW_SPI1_MISO    (pin_A6)
#define MICROPY_HW_SPI1_MOSI    (pin_A7)
#define MICROPY_HW_SPI2_NSS     (pin_B12)
#define MICROPY_HW_SPI2_SCK     (pin_B13)
#define MICROPY_HW_SPI2_MISO    (pin_B14)
#define MICROPY_HW_SPI2_MOSI    (pin_B15)
#define MICROPY_HW_SPI3_NSS     (pin_A4)
#define MICROPY_HW_SPI3_SCK     (pin_C10)
#define MICROPY_HW_SPI3_MISO    (pin_C11)
#define MICROPY_HW_SPI3_MOSI    (pin_C12)

// CAN buses
#define MICROPY_HW_CAN1_TX (pin_B9)
#define MICROPY_HW_CAN1_RX (pin_B8)

my mpconfigboard.mk

MCU_SERIES = l4
CMSIS_MCU = STM32L452xx
AF_FILE = boards/stm32l452_af.csv
LD_FILES = boards/stm32l452xe.ld boards/common_basic.ld
OPENOCD_CONFIG = boards/openocd_stm32l4.cfg
FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py

my stm32l4xx_hal_conf.h (I am not able to compile without the HSE_VALUE)

#ifndef MICROPY_INCLUDED_STM32L4XX_HAL_CONF_H
#define MICROPY_INCLUDED_STM32L4XX_HAL_CONF_H

// Oscillator values in Hz
#define HSE_VALUE (8000000)
#define MSI_VALUE (4000000)
#define LSE_VALUE (32768)
#define EXTERNAL_SAI1_CLOCK_VALUE (48000)
#define EXTERNAL_SAI2_CLOCK_VALUE (48000)

// Oscillator timeouts in ms
#define HSE_STARTUP_TIMEOUT (100)
#define LSE_STARTUP_TIMEOUT (5000)

#include "boards/stm32l4xx_hal_conf_base.h"

#endif // MICROPY_INCLUDED_STM32L4XX_HAL_CONF_H

Please advise on the config or what could be wrong with this board.

Thanks,
Eric.

[bidrohini]

Check if the PLL configuration correctly generates a 48MHz USB clock from the MSI input. This is necessary for USB functionality:
MSI @ 4MHz with PLLN = 40, PLLM = 1, and PLLR = 2 generates 80MHz (SYSCLK).

[Tico06]

Thanks, I'll have a look on this. Do you have some pointers. I had a look on other boards definitions, but not easy to catch the stuff.

[Tico06]

Hi There,
Investigating on this issue I found the following comment in ports/stm32/system_stm32.c:

#if defined(STM32F4) || defined(STM32F7) || defined(STM32G4) || defined(STM32H7) || defined(STM32L4)

/**
  * @brief  System Clock Configuration
  *
  *         The system Clock is configured for F4/F7 as follows:
  *         (HSx should be read as HSE or HSI depending on the value of MICROPY_HW_CLK_USE_HSI)
  *            System Clock source            = PLL (HSx)
  *            SYSCLK(Hz)                     = 168000000
  *            HCLK(Hz)                       = 168000000
  *            AHB Prescaler                  = 1
  *            APB1 Prescaler                 = 4
  *            APB2 Prescaler                 = 2
  *            HSx Frequency(Hz)              = HSx_VALUE
  *            PLL_M                          = HSx_VALUE/1000000
  *            PLL_N                          = 336
  *            PLL_P                          = 4
  *            PLL_Q                          = 7
  *            VDD(V)                         = 3.3
  *            Main regulator output voltage  = Scale1 mode
  *            Flash Latency(WS)              = 5
  *
  *         The system Clock is configured for L4 as follows:
  *            System Clock source            = PLL (MSI)
  *            SYSCLK(Hz)                     = 80000000
  *            HCLK(Hz)                       = 80000000
  *            AHB Prescaler                  = 1
  *            APB1 Prescaler                 = 1
  *            APB2 Prescaler                 = 1
  *            MSI Frequency(Hz)              = MSI_VALUE (4000000)
  *            LSE Frequency(Hz)              = 32768
  *            PLL_M                          = 1
  *            PLL_N                          = 40
  *            PLL_P                          = 7
  *            PLL_Q                          = 2
  *            PLL_R                          = 2 <= This is the source for SysClk, not as on F4/7 PLL_P
  *            Flash Latency(WS)              = 4
  * @param  None
  * @retval None
  *
  * PLL is configured as follows:
  *
  *     VCO_IN
  *         F4/F7 = HSx / M
  *         L4    = MSI / M
  *     VCO_OUT
  *         F4/F7 = HSx / M * N
  *         L4    = MSI / M * N
  *     PLLCLK
  *         F4/F7 = HSx / M * N / P
  *         L4    = MSI / M * N / R
  *     PLL48CK
  *         F4/F7 = HSx / M * N / Q
  *         L4    = MSI / M * N / Q  USB Clock is obtained over PLLSAI1
  *
  *     SYSCLK = PLLCLK
  *     HCLK   = SYSCLK / AHB_PRESC
  *     PCLKx  = HCLK / APBx_PRESC
  *
  * Constraints on parameters:
  *
  *     VCO_IN between 1MHz and 2MHz (2MHz recommended)
  *     VCO_OUT between 192MHz and 432MHz
  *     HSE = 8MHz
  *     HSI = 16MHz
  *     M = 2 .. 63 (inclusive)
  *     N = 192 ... 432 (inclusive)
  *     P = 2, 4, 6, 8
  *     Q = 2 .. 15 (inclusive)
  *
  *     AHB_PRESC=1,2,4,8,16,64,128,256,512
  *     APBx_PRESC=1,2,4,8,16
  *
  * Output clocks:
  *
  * CPU             SYSCLK      max 168MHz
  * USB,RNG,SDIO    PLL48CK     must be 48MHz for USB
  * AHB             HCLK        max 168MHz
  * APB1            PCLK1       max 42MHz
  * APB2            PCLK2       max 84MHz
  *
  * Timers run from APBx if APBx_PRESC=1, else 2x APBx
  */

What I don't understand, it's said constraint on parameter N is 192...432 all inclusive. But the parameters given for L4 is PLL_N = 40. Did I miss something ?