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Merge pull request #10320 from gebart/kinetis/lpuart-osr-dynamic

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kinetis: LPUART: Compute oversampling rate at init
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Alexandre Abadie 2018-12-03 09:11:13 +01:00 committed by GitHub
commit 655fdae982
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1 changed files with 23 additions and 6 deletions
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29
cpu/kinetis/periph/uart.c
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@ -58,9 +58,14 @@
#endif
#endif
#ifndef LPUART_OVERSAMPLING_RATE
/* Use 16x oversampling by default (hardware defaults) */
#define LPUART_OVERSAMPLING_RATE (16)
#ifndef LPUART_OVERSAMPLING_RATE_MIN
/* Use 10x oversampling at minimum, this will be iterated to achieve a better
* baud rate match than otherwise possible with a fixed oversampling rate */
/* Hardware reset default value is an oversampling rate of 16 */
#define LPUART_OVERSAMPLING_RATE_MIN (10)
#endif
#ifndef LPUART_OVERSAMPLING_RATE_MAX
#define LPUART_OVERSAMPLING_RATE_MAX (32)
#endif
/* Default LPUART clock setting to avoid compilation failures, define this in
@ -318,7 +323,6 @@ void UART_4_ISR(void)
static inline void uart_init_lpuart(uart_t uart, uint32_t baudrate)
{
LPUART_Type *dev = uart_config[uart].dev;
uint32_t clk = uart_config[uart].freq;
/* Set LPUART clock source */
#ifdef SIM_SOPT2_LPUART0SRC
@ -339,10 +343,23 @@ static inline void uart_init_lpuart(uart_t uart, uint32_t baudrate)
dev->CTRL = uart_config[uart].mode;
/* calculate baud rate divisor */
uint32_t div = clk / (baudrate * LPUART_OVERSAMPLING_RATE);
uint32_t clk = uart_config[uart].freq;
uint32_t best_err = baudrate;
uint32_t best_osr = LPUART_OVERSAMPLING_RATE_MIN;
/* Use the oversampling rate as a baud rate fine adjust tool */
for (uint32_t osr = LPUART_OVERSAMPLING_RATE_MIN; osr <= LPUART_OVERSAMPLING_RATE_MAX; ++osr) {
uint32_t div = clk / (osr * baudrate);
uint32_t actual_baud = clk / (osr * div);
uint32_t err = ((actual_baud > baudrate) ? actual_baud - baudrate : baudrate - actual_baud);
if (err < best_err) {
best_err = err;
best_osr = osr;
}
}
uint32_t sbr = clk / (best_osr * baudrate);
/* set baud rate */
dev->BAUD = LPUART_BAUD_OSR(LPUART_OVERSAMPLING_RATE - 1) | LPUART_BAUD_SBR(div);
dev->BAUD = LPUART_BAUD_OSR(best_osr - 1) | LPUART_BAUD_SBR(sbr);
/* enable transmitter and receiver + RX interrupt */
dev->CTRL |= LPUART_CTRL_TE_MASK | LPUART_CTRL_RE_MASK | LPUART_CTRL_RIE_MASK;