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stm32_common/uart: add baudrate recalculation based on clk settings #8401

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stm32_common/uart: add baudrate recalculation based on clk settings #8401

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1a2b0e5
stm32_common/periph/uart: add baudrate setting function for uart
fjmolinas Jan 22, 2018
b04e11a
stm32_common/periph/uart: move uart_set_baudrate to periph_cpu_common
fjmolinas Jan 23, 2018
f981ef3
--fixup: change function name
fjmolinas Jan 24, 2018
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17 changes: 17 additions & 0 deletions cpu/stm32_common/include/periph_cpu_common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -306,6 +306,23 @@ uint32_t periph_apb_clk(uint8_t bus);
*/
uint32_t periph_timer_clk(uint8_t bus);

/**
* @brief Recalculate Baudrate for UART device
*
* The UART device will be initialized with the following configuration:
* - 8 data bits
* - no parity
* - 1 stop bit
* - baudrate as given
*
* @param[in] uart UART device to initialize
* @param[in] baudrate desired baudrate in baud/s
*
* @return UART_OK on success
* @return UART_NOBAUD on inapplicable baudrate
*/
int periph_uart_set_baudrate(unsigned int uart, uint32_t baudrate);

/**
* @brief Enable the given peripheral clock
*
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63 changes: 50 additions & 13 deletions cpu/stm32_common/periph/uart.c
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Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,10 @@
#include "periph/uart.h"
#include "periph/gpio.h"

#define RXENABLE (USART_CR1_RE | USART_CR1_RXNEIE)
#define RXENABLE (USART_CR1_RE | USART_CR1_RXNEIE)

#define UART_8X_OVERSAMPLING 8
#define UART_16X_OVERSAMPLING 16
/**
* @brief Allocate memory to store the callback functions
*/
Expand All @@ -43,19 +45,57 @@ static inline USART_TypeDef *dev(uart_t uart)
return uart_config[uart].dev;
}

int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
{
int periph_uart_set_baudrate(uart_t uart, uint32_t baudrate) {
uint16_t mantissa;
uint8_t fraction;
uint32_t clk;
uint32_t uart_clk;

uart_clk = periph_apb_clk(uart_config[uart].bus)/baudrate;

if (uart_clk < 8) {
/* clock is too slow for using UART with specified baudrate */
periph_clk_dis(uart_config[uart].bus, uart_config[uart].rcc_mask);
return UART_NOBAUD;
} else {
/* Disable UART. Setting BRR on enabled USART1 sometimes somehow results in Hard Fault */
dev(uart)->CR1 &= ~USART_CR1_UE;

/* choose between 8x and 16x oversampling */
/* 16x is preferred, but is not possible on low clock frequency */
#ifdef USART_CR1_OVER8
if (uart_clk < 16) {
dev(uart)->CR1 |= USART_CR1_OVER8;
mantissa = (uint16_t)(uart_clk / UART_8X_OVERSAMPLING);
fraction = (uint8_t)(uart_clk - (mantissa * UART_8X_OVERSAMPLING));
dev(uart)->BRR = ((mantissa & 0x0fff) << 4) | (fraction & 0x07);
} else {
dev(uart)->CR1 &= ~USART_CR1_OVER8;
mantissa = (uint16_t)(uart_clk / UART_16X_OVERSAMPLING);
fraction = (uint8_t)(uart_clk - (mantissa * UART_16X_OVERSAMPLING));
dev(uart)->BRR = ((mantissa & 0x0fff) << 4) | (fraction & 0x0f);
}
#else
mantissa = (uint16_t)(uart_clk / UART_16X_OVERSAMPLING);
fraction = (uint8_t)(uart_clk - (mantissa * UART_16X_OVERSAMPLING));
dev(uart)->BRR = ((mantissa & 0x0fff) << 4) | (fraction & 0x0f);
#endif

/* Enable UART */
dev(uart)->CR1 |= USART_CR1_UE;

return UART_OK;
}
}

int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg) {
assert(uart < UART_NUMOF);

/* save ISR context */
isr_ctx[uart].rx_cb = rx_cb;
isr_ctx[uart].arg = arg;

/* configure TX pin */
/* configure RX and TX pin */
gpio_init(uart_config[uart].rx_pin, GPIO_IN);
gpio_init(uart_config[uart].tx_pin, GPIO_OUT);
/* set TX pin high to avoid garbage during further initialization */
gpio_set(uart_config[uart].tx_pin);
Expand Down Expand Up @@ -93,18 +133,15 @@ int uart_init(uart_t uart, uint32_t baudrate, uart_rx_cb_t rx_cb, void *arg)
dev(uart)->CR3 = 0;

/* calculate and apply baudrate */
clk = periph_apb_clk(uart_config[uart].bus) / baudrate;
mantissa = (uint16_t)(clk / 16);
fraction = (uint8_t)(clk - (mantissa * 16));
dev(uart)->BRR = ((mantissa & 0x0fff) << 4) | (fraction & 0x0f);
if (uart_set_baudrate(uart, baudrate) != UART_OK) {
return UART_NOBAUD;
}

dev(uart)->CR1 = (USART_CR1_UE | USART_CR1_TE);
/* enable RX interrupt if applicable */
if (rx_cb) {
NVIC_EnableIRQ(uart_config[uart].irqn);
dev(uart)->CR1 = (USART_CR1_UE | USART_CR1_TE | RXENABLE);
}
else {
dev(uart)->CR1 = (USART_CR1_UE | USART_CR1_TE);
dev(uart)->CR1 |= RXENABLE;
}

#ifdef MODULE_STM32_PERIPH_UART_HW_FC
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