driver: serial: uart_stm32: Calculate suitable PRESCALER value
Current driver set a fixed prescaler value for the lpuart
that caused certain baudrate configurations to fail due to
LPUARTDIV overflow the LPUART_BRR register.
This PR attempt to calculate a suitable PRESCALER for the
selected baudrate, throws error and return if it couldn't get
an optimal one.
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>
diff --git a/drivers/serial/uart_stm32.c b/drivers/serial/uart_stm32.c
index 0dfbad9..67ca825 100644
--- a/drivers/serial/uart_stm32.c
+++ b/drivers/serial/uart_stm32.c
@@ -51,6 +51,34 @@
#define UART_STRUCT(dev) \
((USART_TypeDef *)(DEV_CFG(dev))->uconf.base)
+#if HAS_LPUART_1
+#ifdef USART_PRESC_PRESCALER
+uint32_t lpuartdiv_calc(const uint64_t clock_rate, const uint16_t presc_idx,
+ const uint32_t baud_rate)
+{
+ uint64_t lpuartdiv;
+
+ lpuartdiv = clock_rate / LPUART_PRESCALER_TAB[presc_idx];
+ lpuartdiv *= LPUART_LPUARTDIV_FREQ_MUL;
+ lpuartdiv += baud_rate / 2;
+ lpuartdiv /= baud_rate;
+
+ return (uint32_t)lpuartdiv;
+}
+#else
+uint32_t lpuartdiv_calc(const uint64_t clock_rate, const uint32_t baud_rate)
+{
+ uint64_t lpuartdiv;
+
+ lpuartdiv = clock_rate * LPUART_LPUARTDIV_FREQ_MUL;
+ lpuartdiv += baud_rate / 2;
+ lpuartdiv /= baud_rate;
+
+ return (uint32_t)lpuartdiv;
+}
+#endif /* USART_PRESC_PRESCALER */
+#endif /* HAS_LPUART_1 */
+
#define TIMEOUT 1000
#ifdef CONFIG_PM
@@ -92,13 +120,39 @@
return;
}
-
#if HAS_LPUART_1
if (IS_LPUART_INSTANCE(UartInstance)) {
+ uint32_t lpuartdiv;
+#ifdef USART_PRESC_PRESCALER
+ uint8_t presc_idx;
+ uint32_t presc_val;
+
+ for (presc_idx = 0; presc_idx < ARRAY_SIZE(LPUART_PRESCALER_TAB); presc_idx++) {
+ lpuartdiv = lpuartdiv_calc(clock_rate, presc_idx, baud_rate);
+ if (lpuartdiv >= LPUART_BRR_MIN_VALUE && lpuartdiv <= LPUART_BRR_MASK) {
+ break;
+ }
+ }
+
+ if (presc_idx == ARRAY_SIZE(LPUART_PRESCALER_TAB)) {
+ LOG_ERR("Unable to set %s to %d", dev->name, baud_rate);
+ return;
+ }
+
+ presc_val = presc_idx << USART_PRESC_PRESCALER_Pos;
+
+ LL_LPUART_SetPrescaler(UartInstance, presc_val);
+#else
+ lpuartdiv = lpuartdiv_calc(clock_rate, baud_rate);
+ if (lpuartdiv < LPUART_BRR_MIN_VALUE || lpuartdiv > LPUART_BRR_MASK) {
+ LOG_ERR("Unable to set %s to %d", dev->name, baud_rate);
+ return;
+ }
+#endif /* USART_PRESC_PRESCALER */
LL_LPUART_SetBaudRate(UartInstance,
clock_rate,
#ifdef USART_PRESC_PRESCALER
- LL_USART_PRESCALER_DIV1,
+ presc_val,
#endif
baud_rate);
} else {
