Unable to init UART with FIFO enabled

[SibertEnovates]

Description of defect

STM32G0B0 has UARTS which have a FIFO which can be turned on or off. They cannot seem to be turned on when initializing the UART (which happens a lot in mbed: when the BufferedSerial is created, when the format is changed or when the baudrate is changed). There are HAL functions to enable the FIFO but the initialize wipes this setting.

The inability to enable FIFO on initialization is two-fold.
First of all, the general STM serial_api.c does't seem to allow this. init_uart contains this code:

#if defined(UART_FIFOMODE_DISABLE) // G0/H7/L4/L5/WB
    huart->FifoMode = UART_FIFOMODE_DISABLE;
#endif

UART_FIFOMODE_DISABLE is defined in stm32g0xx_hal_uart_ex.h:

#define UART_FIFOMODE_DISABLE       0x00000000U       /*!< FIFO mode disable */
#define UART_FIFOMODE_ENABLE        USART_CR1_FIFOEN  /*!< FIFO mode enable  */

So I'm not sure how to convince the init_uart in serial_api.c to set FifoMode to enable this.

Second, setting the FifoMode does not seems to be implemented in UART_SetConfig in stm32g0xx_hal_uart (maybe something to raise in STM32CubeG0) . The FIFOMode is part of the CR1 register, so I would expect to see it in this part of the code:

tmpreg = (uint32_t)huart->Init.WordLength | huart->Init.Parity | huart->Init.Mode | huart->Init.OverSampling;
MODIFY_REG(huart->Instance->CR1, USART_CR1_FIELDS, tmpreg);

I would suggest UART_InitTypeDef should be extended to contain the FIFOMode as well and change UART_SetConfig to consider this setting. I also think that using the UART_FIFOMODE_DISABLE define is the wrong define to determine whether or not the FIFO should be enabled and should be changed by a define generated in mbed_config.h.

I'm obviously willing to make these changes but I'd like your thoughts on the issue first before I fix this.

Target(s) affected by this defect ?

STM32G0B0

Toolchain(s) (name and version) displaying this defect ?

cmake_gcc_arm

What version of Mbed-os are you using (tag or sha) ?

mbed-os-6.15.1

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

Not applicable

How is this defect reproduced ?

Create a new BufferedSerial and check if the FIFOEN bit is enabled in the UART CR1 register

[0xc0170]

cc @ARMmbed/team-st-mcd

[jeromecoutant]

Hi
I don't know his feature...

But I have a look in the code.
Seems that if you are patching the init function with:
huart->FifoMode = UART_FIFOMODE_ENABLE;
It seems that you have to call HAL_UARTEx_EnableFifoMode() ?

Why this is not done in UART_SetConfig, yes, you should ask in
https://github.com/STMicroelectronics/STM32CubeG0 :-)

[SibertEnovates]

But I have a look in the code. Seems that if you are patching the init function with: huart->FifoMode = UART_FIFOMODE_ENABLE; It seems that you have to call HAL_UARTEx_EnableFifoMode() ?

I do think the whole serial initialisation needs an overhaul. The init is done based on defines from the HAL, which are intended as aliasses for the register values. A great example is setting the prescaler:

#if defined(UART_PRESCALER_DIV1) // G0/H7/L4/L5/WB
    huart->Init.ClockPrescaler = UART_PRESCALER_DIV1;
#endif

Looking at this define:

#define UART_PRESCALER_DIV1    0x00000000U  /*!< fclk_pres = fclk     */
#define UART_PRESCALER_DIV2    0x00000001U  /*!< fclk_pres = fclk/2   */
#define UART_PRESCALER_DIV4    0x00000002U  /*!< fclk_pres = fclk/4   */
#define UART_PRESCALER_DIV6    0x00000003U  /*!< fclk_pres = fclk/6   */
#define UART_PRESCALER_DIV8    0x00000004U  /*!< fclk_pres = fclk/8   */
#define UART_PRESCALER_DIV10   0x00000005U  /*!< fclk_pres = fclk/10  */
#define UART_PRESCALER_DIV12   0x00000006U  /*!< fclk_pres = fclk/12  */
#define UART_PRESCALER_DIV16   0x00000007U  /*!< fclk_pres = fclk/16  */
#define UART_PRESCALER_DIV32   0x00000008U  /*!< fclk_pres = fclk/32  */
#define UART_PRESCALER_DIV64   0x00000009U  /*!< fclk_pres = fclk/64  */
#define UART_PRESCALER_DIV128  0x0000000AU  /*!< fclk_pres = fclk/128 */
#define UART_PRESCALER_DIV256  0x0000000BU  /*!< fclk_pres = fclk/256 */

I'm either missing something but those defines don't look to me like they should be used to base the initial values on, but rather to set the register based on the configuration.

Why this is not done in UART_SetConfig, yes, you should ask in https://github.com/STMicroelectronics/STM32CubeG0 :-)

I'll check in with those people for the UART_SetConfig.

[jeromecoutant]

Hi
Any update ?
Thx