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Merge pull request #17186 from benpicco/cpu/sam0_common/uart-frac

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cpu/sam0_common: uart: set oversampling based on baud rate
This commit is contained in:
Dylan Laduranty 2021-11-15 21:53:19 +01:00 committed by GitHub
commit 8f4ef1eb75
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1 changed files with 24 additions and 7 deletions
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31
cpu/sam0_common/periph/uart.c
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@ -95,14 +95,16 @@ static inline void _reset(SercomUsart *dev)
#endif
}
static void _set_baud(uart_t uart, uint32_t baudrate)
static void _set_baud(uart_t uart, uint32_t baudrate, uint32_t f_src)
{
const uint32_t f_src = sam0_gclk_freq(uart_config[uart].gclk_src);
#if IS_ACTIVE(CONFIG_SAM0_UART_BAUD_FRAC)
/* Asynchronous Fractional */
uint32_t baud = (((f_src * 8) / baudrate) / 16);
dev(uart)->BAUD.FRAC.FP = (baud % 8);
dev(uart)->BAUD.FRAC.BAUD = (baud / 8);
/* BAUD + FP / 8 = f_src / (S * f_baud) */
/* BAUD * 8 + FP = (8 * f_src) / (S * f_baud) */
/* S * (BAUD + 8 * FP) = (8 * f_src) / f_baud */
uint32_t baud = (f_src * 8) / baudrate;
dev(uart)->BAUD.FRAC.FP = (baud >> 4) & 0x7; /* baud / 16 */
dev(uart)->BAUD.FRAC.BAUD = baud >> 7; /* baud / (8 * 16) */
#else
/* Asynchronous Arithmetic */
/* BAUD = 2^16 * (2^0 - 2^4 * f_baud / f_src) */
@ -180,12 +182,27 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
/* configure clock generator */
sercom_set_gen(dev(uart), uart_config[uart].gclk_src);
uint32_t f_src = sam0_gclk_freq(uart_config[uart].gclk_src);
#if IS_ACTIVE(CONFIG_SAM0_UART_BAUD_FRAC)
uint32_t sampr;
/* constraint: f_baud ≤ f_src / S */
if (baudrate * 16 > f_src) {
/* 8x oversampling */
sampr = SERCOM_USART_CTRLA_SAMPR(0x3);
f_src <<= 1;
} else {
/* 16x oversampling */
sampr = SERCOM_USART_CTRLA_SAMPR(0x1);
}
#endif
/* set asynchronous mode w/o parity, LSB first, TX and RX pad as specified
* by the board in the periph_conf.h, x16 sampling and use internal clock */
dev(uart)->CTRLA.reg = SERCOM_USART_CTRLA_DORD
#if IS_ACTIVE(CONFIG_SAM0_UART_BAUD_FRAC)
/* enable Asynchronous Fractional mode */
| SERCOM_USART_CTRLA_SAMPR(0x1)
| sampr
#endif
| SERCOM_USART_CTRLA_TXPO(uart_config[uart].tx_pad)
| SERCOM_USART_CTRLA_RXPO(uart_config[uart].rx_pad)
@ -197,7 +214,7 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
}
/* calculate and set baudrate */
_set_baud(uart, baudrate);
_set_baud(uart, baudrate, f_src);
/* enable transmitter, and configure 8N1 mode */
if (uart_config[uart].tx_pin != GPIO_UNDEF) {