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[STM32F3]: fix for uart baudrate. #2099

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[STM32F3]: fix for uart baudrate. #2099

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9 changes: 7 additions & 2 deletions hal/targets/hal/TARGET_STM/TARGET_STM32F3/serial_api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@
#include "pinmap.h"
#include <string.h>
#include "PeripheralPins.h"
#include "mbed_error.h"

#define UART_NUM (5)

Expand Down Expand Up @@ -69,8 +70,12 @@ static void init_uart(serial_t *obj)
// Disable the reception overrun detection
UartHandle.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_RXOVERRUNDISABLE_INIT;
UartHandle.AdvancedInit.OverrunDisable = UART_ADVFEATURE_OVERRUN_DISABLE;

HAL_UART_Init(&UartHandle);
/* uAMR & ARM: Call to UART init is done between reset of pre-initialized variables */
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misaligned comment. Did you consider doing this as part of the HAL init mbed_sdk_init(), I assume this might be required for more than just UART.

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I am fixing this locally, will merge it manually

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There are tabs, please use spaces

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On Arm , or uARM :SystemInit is called after boot (SystemInit write SystemCoreClock and call HAL_Init), then __main is called, this will perform zero initialized of bss , recopy of initialized variable (this will change the value of SystemCoreClock), then _initio calls init_serial (which calls init_uart, init_uart works properly if SystemCoreClock is correctly sets)
Later before calling main , mbed_sdk_init is called, this will update again SystemCoreClock and do again HAL_Init) which will allow a correct usage of UART or other peripheral with HAL.

On GCC_ARM, as zero initialized of bss , recopy of initialized variable is done early after reset and before SystemInit, the value of SystemCoreClock remains un-changed after SystemInit, so with GCC_ARM no need to add this fix in init_uart or in mbed_sdk_init.

On IAR , SystemInit is called after boot (SystemInit write SystemCoreClock and call HAL_Init), then __iar_program_start, this calls __iar_data_init3 which does zero initialized of bss, recopy of initialized data (this will change the value of SystemCoreClock), then mbed_sdk_init is called (This will put the value of systemCoreClock to the correct value) and the init_uart is called at the 1st printf . On IAR the fix in init_uart is not needed.

=> The Init is different according to compilers , this leads to un-confortable fix on ARM and IAR, due the late zero initiliazed, or recopy of initialized data for ARM, IAR compiler.

/* and before HAL Init. SystemCoreClock init required here */
SystemCoreClockUpdate();
if (HAL_UART_Init(&UartHandle) != HAL_OK) {
error("Cannot initialize UART\n");
}
}

void serial_init(serial_t *obj, PinName tx, PinName rx)
Expand Down