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stmhal: L4: Adapt UART HAL to avoid 64-bit integer division.

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64-bit integer division brings a dependency on library functions. It is
avoided here by dividing fck and baud by a common divisior.  The error
is the better (1/(2*0x300)) as with 64 bit division (1/(0x300)).
This commit is contained in:
Tobias Badertscher 2016-03-16 16:51:13 +01:00 committed by Damien George
parent f4942db044
commit d4c3349957
2 changed files with 42 additions and 1 deletions
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5
stmhal/hal/l4/inc/stm32l4xx_hal_uart.h
View File

@ -962,7 +962,8 @@ typedef struct
* @param __BAUD__: Baud rate set by the user.
* @retval Division result
*/
#define UART_DIV_LPUART(__PCLK__, __BAUD__) (((uint64_t)(__PCLK__)*256)/((__BAUD__)))
/* FIXME tobbad Adapted to avoid 64 bit division. */
#define UART_DIV_LPUART(__PCLK__, __BAUD__) HAL_UART_CalcBrr((__PCLK__), (__BAUD__))
/** @brief BRR division operation to set BRR register in 8-bit oversampling mode.
* @param __PCLK__: UART clock.
@ -1369,6 +1370,8 @@ void UART_AdvFeatureConfig(UART_HandleTypeDef *huart);
/**
* @}
*/
/* Functions added by micropython */
uint32_t HAL_UART_CalcBrr(uint32_t fck, uint32_t baud);
#ifdef __cplusplus
}

38
stmhal/hal/l4/src/stm32l4xx_hal_uart.c
View File

@ -2101,6 +2101,44 @@ static HAL_StatusTypeDef UART_Receive_IT(UART_HandleTypeDef *huart)
}
}
/**
* @brief Calculate register BRR value without using uint64.
* @note This function is added by the micropython project.
* @param fck: Input clock frequency to the uart block in Hz.
* @param baud: baud rate should be one of {300, 600, 1200, 2400, 4800, 9600, 19200, 57600, 115200}.
* @retval BRR value
*/
uint32_t HAL_UART_CalcBrr(uint32_t fck, uint32_t baud)
{
const struct
{
uint32_t limit;
uint32_t div;
} comDiv[]= {
{1<<31, 300 }, /* must be >= 256 */
{1<<30, 150 }, /* must be >= 128 */
{1<<29, 75 }, /* must be >= 64 */
{1<<28, 50 }, /* must be >= 32 */
{1<<27, 20 }, /* must be >= 16 */
{1<<26, 10 }, /* must be >= 8 */
{1<<25, 5 }, /* must be >= 4 */
{1<<24, 2 } /* must be >= 2 */
};
const uint32_t comDivCnt = sizeof(comDiv)/sizeof(comDiv[0]);
uint8_t i;
for (i=0; i<comDivCnt ;i++)
{
if (fck >= comDiv[i].limit)
{
fck /= comDiv[i].div;
baud /= comDiv[i].div;
break;
}
}
return (fck<<8)/baud;
}
/**
* @}
*/