Potential issue with UART library?

[csajisynco]

I'm trying to set up up USART1 on my STM32H735. I call these functions to setup a new serialPort instance.

HardwareSerial *serialPort = new HardwareSerial(USART1);
serialPort->setRx(PA10);
serialPort->setTx(PA9);
serialPort->begin(460800);

In the function "uart_init" located in "uart.c", it goes through initializing the huart struct. However, the ClockPrescaler, next gets set anywhere and is loaded with a default garbage value.

When the huart struct is passed to the function "UART_SetConfig", it faults on the line:

    usartdiv = (uint32_t)(UART_DIV_LPUART(pclk, huart->Init.BaudRate, huart->Init.ClockPrescaler));

because huart->Init.ClockPrescaler is some random garbage value.

Is this an issue with the library itself?

[fpistm]

Hi,
the value is computed by the driver. Anyway, it relies on the LPUART clock source defined by the system core clock config.
As you required an higher baudrate, I guess the clock source is correct for this use case.
LPUART requires:
/*

• Note that LPUART clock source must be in the range
• [3 x baud rate, 4096 x baud rate]
• check Reference Manual
  */
  So in a general case the provided clock source is set to be able to perform 9600.
  Try to redefine the void SystemClock_Config(void) with a different LPUAT clock source allowing 460800.

[csajisynco]

But I'm not trying to use the LPUART module. I want to use USART1. Why would it pull the value from there?

[fpistm]

Which board you used?

[csajisynco]

Which board you used?

This is a custom board using the STM32H735RGVX. I have a UART lines connected to PA10 (RX) and PA9 (TX). which should be USART1. I am using PlatformIO as well.

Some things also to note. I have a 25 MHz oscillator connected to PH0 and PH1. I currently don't have any 32KHz oscillator connected to PC14 and PC15, which I assume is fine.

I generated the void SystemClock_Config(void) using CubeMX. I've configured all my peripherals and enabled the HSE and disabled the LSE.

I've combined the SystemClock_Config and PeriphCommonClock_Config into one function:

/**

• Generated from CubeMX
  */

WEAK void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

/** Supply configuration update enable
*/
HAL_PWREx_ConfigSupply(PWR_DIRECT_SMPS_SUPPLY);

/** Configure the main internal regulator output voltage
*/
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE0);

while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}

/** Initializes the RCC Oscillators according to the specified parameters

• in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSIState = RCC_HSI_DIV1;
  RCC_OscInitStruct.HSICalibrationValue = 64;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 2;
  RCC_OscInitStruct.PLL.PLLN = 44;
  RCC_OscInitStruct.PLL.PLLP = 1;
  RCC_OscInitStruct.PLL.PLLQ = 2;
  RCC_OscInitStruct.PLL.PLLR = 2;
  RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_3;
  RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
  RCC_OscInitStruct.PLL.PLLFRACN = 0;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
  Error_Handler();
  }

/** Initializes the CPU, AHB and APB buses clocks
*/
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2
|RCC_CLOCKTYPE_D3PCLK1|RCC_CLOCKTYPE_D1PCLK1;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;

if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_3) != HAL_OK)
{
Error_Handler();
}

/** Initializes the peripherals clock
*/

RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};

PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI2|RCC_PERIPHCLK_SPI1;
PeriphClkInitStruct.PLL2.PLL2M = 2;
PeriphClkInitStruct.PLL2.PLL2N = 16;
PeriphClkInitStruct.PLL2.PLL2P = 2;
PeriphClkInitStruct.PLL2.PLL2Q = 2;
PeriphClkInitStruct.PLL2.PLL2R = 2;
PeriphClkInitStruct.PLL2.PLL2RGE = RCC_PLL2VCIRANGE_3;
PeriphClkInitStruct.PLL2.PLL2VCOSEL = RCC_PLL2VCOWIDE;
PeriphClkInitStruct.PLL2.PLL2FRACN = 0;
PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL2;
if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
{
Error_Handler();
}
}

[fpistm]

So you used LPUART1 as PA9 and PA10 are :

Arduino_Core_STM32/variants/STM32H7xx/H725R(E-G)V_H735RGV/PeripheralPins.c

Line 179 in d8062ae

{PA_9, LPUART1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_LPUART)},

Do this:

serialPort->setRx(PA10_ALT1);
serialPort->setTx(PA9_ALT1);

[csajisynco]

OK. That's why PIO is not supported here as it is in general way not updated.

I've update the library to use the latest version. This resolved the clockPrescaler having garbage values.

However, there is still the issue of _written, _rx_invert, _tx_invert, and _data_invert flags in the HardwareSerial class being initialized to garbage values as well. as shown in the last image I sent.

There is no function in the HardwareSerial class to disable these flags, only enable them. Like clockPrescaler in the old version of stm32duino, there is no function to initialize these flags.

If I use the debugger to set these values to false, my UART works properly.

The issue can be resolved by initializing these variables to false.

I believe an issue needs to opened to resolve this issue. I would, but I'm not sure how to go about that.

[fpistm]

Again linked to pio.
Not seen under Arduino. The variable are init to 0 by default.

Anyway feel free to provide a PR.

[fpistm]

Hereafter debug under Arduino IDE 2:

As you can see all are properly set.

[csajisynco]

Hmm weird. Maybe it's just a quirk of PlatformIO. I still get the issue, but I'll just initialization the variables manually by modify the HardwareSerial class.

Thanks for your help!

[fpistm]

IIWR the trick is that ggc used by default -fzero-initialized-in-bss except in Ada.
Anyway, it can be source of issue like the one you have.
So it is maybe better to properly init them. Feel free to provide a PR like this you will not have to update the class each time the core is updated.