Posted on November 07, 2016 at 04:29I've found a bug in source: ''stm32f10x_usart.c'', in function ''USART_Init'', where it calculates the BRR register value. In version 3.5.0 it starts from line 245, till 275.
A few examples of good, and bad results, assuming a 72MHz clock (36MHz apb clock, 8x oversampling disabled):
Baud: 4839; Calculated tmpreg: 0x1d00; Baud rate with this BRR: 4849; Expected BRR: 0x1d10.
Baud: 225000; Calculated tmpreg: 0xa0; Baud rate with this BRR: 225000;
Baud 225001; Calculated tmpreg: 0x90; Baud rate with this BRR: 250000; Expected BRR: 0xa0.
Baud: 226415; Calculated tmpreg: 0x9f; Baud rate with this BRR: 226415;
Baud: 250001; Calculated tmpreg: 0x80; Baud rate with this BRR: 281250; Expected BRR: 0x90.
The whole calculation can be corrected, and simplyfied without needing any intermediate variable:
tmpreg = (apbclock + (USART_InitStruct->USART_BaudRate >> 1)) / (USART_InitStruct->USART_BaudRate);
if ((USARTx->CR1 & CR1_OVER8_Set) != 0)
{
tmpreg = ((tmpreg & ~7) << 1) | (tmpreg & 0x7);
}
#stm32f10x-usart-library-bug
