diff options
| author | Christian Tacke <Christian.Tacke+libopencm3@cosmokey.com> | 2018-03-04 16:19:19 +0300 |
|---|---|---|
| committer | Karl Palsson <karlp@tweak.net.au> | 2018-08-17 03:15:01 +0300 |
| commit | c55ec70f496d61c8731ccc08e15af500ab61beee (patch) | |
| tree | 54f0ee7a5f22b2c09e1b3af6b0e6eda30e927a10 | |
| parent | 49a8c041ff03796a10e944cb88c60ef07b4fc86e (diff) | |
STM32: USART: Fix baudrate calculation for LPUART1
LPUART1 needs BRR to be 256 times the normal value.
Doing this with 64 bit math would work, but that pulls in quite a lot of
code for every platform, even if they don't have LPUART.
A little bit of maths, thanks to zyp on irc, lets us keep it in 32bit,
provided people don't try and use > 16MBaud on LPUARTs
Originally tracked via https://github.com/libopencm3/libopencm3/pull/888
| -rw-r--r-- | lib/stm32/common/usart_common_all.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/lib/stm32/common/usart_common_all.c b/lib/stm32/common/usart_common_all.c index 4865ef1f..2c7e9a6d 100644 --- a/lib/stm32/common/usart_common_all.c +++ b/lib/stm32/common/usart_common_all.c @@ -42,6 +42,9 @@ USART1/6) or the APB low-speed prescaler clock (for other USARTs). These values must be correctly set before calling this function (refer to the rcc_clock_setup-* functions in RCC). +Note: For LPUART, baudrates over 2**24 (~16.7 Mbaud) may overflow +the calculation and are therefore not supported by this function. + @param[in] usart unsigned 32 bit. USART block register address base @ref usart_reg_base @param[in] baud unsigned 32 bit. Baud rate specified in Hz. @@ -70,7 +73,15 @@ void usart_set_baudrate(uint32_t usart, uint32_t baud) * Note: We round() the value rather than floor()ing it, for more * accurate divisor selection. */ - USART_BRR(usart) = ((2 * clock) + baud) / (2 * baud); +#ifdef LPUART1 + if (usart == LPUART1) { + USART_BRR(usart) = (clock / baud) * 256 + + ((clock % baud) * 256 + baud / 2) / baud; + return; + } +#endif + + USART_BRR(usart) = (clock + baud / 2) / baud; } /*---------------------------------------------------------------------------*/ |