UART: fix bug in baudrate->BRR #14
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bvernoux
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May 20, 2015
UART: fix bug in baudrate->BRR
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Thanks for that amazing fix ;-) |
doegox
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May 21, 2015
There was a bug in ST UART driver when OVERSAMPLING_8. At the moment micropython is only using OVERSAMPLING_16 so this bug is not affecting current micropython fw. But if one day one wants to enable higher baudrates (~5.5M to 10.5M) and use OVERSAMPLING_8 the bug is triggered (and e.g. setting 7M would give an actual 10.5M baudrate). This bug was revealed when playing around with the native firmware of hydrabus, see hydrabus/hydrafw#14 Source: STM32F405 reference manual, 30.3.4 page 965: USARTDIV is an unsigned fixed point number that is coded on the USART_BRR register. Note: • When OVER8=0, the fractional part is coded on 4 bits and programmed by the DIV_fraction[3:0] bits in the USART_BRR register • When OVER8=1, the fractional part is coded on 3 bits and programmed by the DIV_fraction[2:0] bits in the USART_BRR register, and bit DIV_fraction[3] must be kept cleared.
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Some UART speeds were incorrectly set and reported.
Source:
STM32F405 reference manual
30.3.4 page 965:
USARTDIV is an unsigned fixed point number that is coded on the USART_BRR register.
Note:
• When OVER8=0, the fractional part is coded on 4 bits and programmed by the DIV_fraction[3:0] bits in the USART_BRR register
• When OVER8=1, the fractional part is coded on 3 bits and programmed by the DIV_fraction[2:0] bits in the USART_BRR register, and bit DIV_fraction[3] must be kept cleared.