bsps/arm/stm32f4: Enable USART RX interrupts

Hi all, this is my first email patch submission and my first contribution to RTEMS, so please give any
feedback you have!

This patch enables interrupt driven data reception on USART ports on
STM32F4 series chips. This feature is gated behind the config flag
BSP_CONSOLE_USE_INTERRUPTS. If this flag is not set to True, the older
polling implementation will be used. I tested this feature on STM32F401CE
(blackpill) and STM32 Nucleo F411RE boards, with both capable of keeping
up with a 115200 baud continous data stream. With the older polling
implementation, both would drop bytes at 9600 baud. In addition, I
updated the implementation of usart_set_attributes to support changing
the baud rate of the USART port based on the input speed.

1 files changed, 63 insertions, 7 deletions

diff --git a/bsps/arm/stm32f4/console/usart.c b/bsps/arm/stm32f4/console/usart.c
index 37566ef9d7..727d4b1799 100644
--- a/bsps/arm/stm32f4/console/usart.c
+++ b/bsps/arm/stm32f4/console/usart.c
@@ -14,6 +14,8 @@
 #include <bsp/irq.h>
 #include <bsp/usart.h>
 #include <bsp/stm32f4.h>
+#include <termios.h>
+#include <string.h>
 
 static volatile stm32f4_usart *usart_get_regs(const console_tbl *ct)
 {
@@ -27,6 +29,24 @@ static rtems_vector_number usart_get_irq_number(const console_tbl *ct)
 }
 #endif
 
+#ifdef BSP_CONSOLE_USE_INTERRUPTS
+/**
+ * Read characters in an interrupt
+ */
+static void stm32f4_usart_interrupt(void *arg)
+{
+  rtems_termios_tty *tty = (rtems_termios_tty *) arg;
+  const console_tbl *ct = Console_Port_Tbl [tty->minor];
+  volatile stm32f4_usart *usart = usart_get_regs(ct);
+
+  while ((usart->sr & STM32F4_USART_SR_RXNE) == STM32F4_USART_SR_RXNE)
+  {
+    char data = STM32F4_USART_DR_GET(usart->dr);
+    rtems_termios_enqueue_raw_characters(tty, &data, sizeof(data));
+  }
+}
+#endif
+
 static const stm32f4_rcc_index usart_rcc_index [] = {
   STM32F4_RCC_USART1,
   STM32F4_RCC_USART2,
@@ -128,29 +148,50 @@ static void usart_initialize(int minor)
   usart->cr2 = 0;
   usart->cr3 = 0;
   usart->bbr = usart_get_bbr(usart, pclk, baud);
-  usart->cr1 = STM32F4_USART_CR1_UE
-    | STM32F4_USART_CR1_TE
-    | STM32F4_USART_CR1_RE;
+  usart->cr1 = STM32F4_USART_CR1_UE // UART enable
+#ifdef BSP_CONSOLE_USE_INTERRUPTS
+    | STM32F4_USART_CR1_RXNEIE // RX interrupt
+#endif
+    | STM32F4_USART_CR1_TE  // TX enable
+    | STM32F4_USART_CR1_RE; // RX enable
 }
 
 static int usart_first_open(int major, int minor, void *arg)
 {
+  rtems_status_code sc = RTEMS_SUCCESSFUL;
   rtems_libio_open_close_args_t *oc = (rtems_libio_open_close_args_t *) arg;
-  struct rtems_termios_tty *tty = (struct rtems_termios_tty *) oc->iop->data1;
+  rtems_termios_tty *tty = (struct rtems_termios_tty *) oc->iop->data1;
   const console_tbl *ct = Console_Port_Tbl [minor];
   console_data *cd = &Console_Port_Data [minor];
 
   cd->termios_data = tty;
   rtems_termios_set_initial_baud(tty, ct->ulClock);
 
-  return 0;
+#ifdef BSP_CONSOLE_USE_INTERRUPTS
+  sc = rtems_interrupt_handler_install(ct->ulIntVector,
+      ct->sDeviceName,
+      RTEMS_INTERRUPT_UNIQUE,
+      stm32f4_usart_interrupt,
+      tty);
+#endif
+
+  return sc;
 }
 
 static int usart_last_close(int major, int minor, void *arg)
 {
-  return 0;
+  rtems_status_code sc = RTEMS_SUCCESSFUL;
+#ifdef BSP_CONSOLE_USE_INTERRUPTS
+  rtems_libio_open_close_args_t *oc = (rtems_libio_open_close_args_t *) arg;
+  rtems_termios_tty *tty = (struct rtems_termios_tty *) oc->iop->data1;
+  const console_tbl *ct = Console_Port_Tbl [minor];
+
+  sc = rtems_interrupt_handler_remove(ct->ulIntVector, stm32f4_usart_interrupt, tty);
+#endif
+  return sc;
 }
 
+#ifndef BSP_CONSOLE_USE_INTERRUPTS
 static int usart_read_polled(int minor)
 {
   const console_tbl *ct = Console_Port_Tbl [minor];
@@ -162,6 +203,7 @@ static int usart_read_polled(int minor)
     return -1;
   }
 }
+#endif
 
 static void usart_write_polled(int minor, char c)
 {
@@ -190,16 +232,30 @@ static ssize_t usart_write_support_polled(
   return n;
 }
 
+/**
+ * Configure settings from a termios call to tcsetattr()
+ */
 static int usart_set_attributes(int minor, const struct termios *term)
 {
-  return -1;
+  console_tbl *ct = Console_Port_Tbl[minor];
+  volatile stm32f4_usart *usart = usart_get_regs(ct);
+  uint32_t pclk = usart_get_pclk(ct);
+  uint32_t baud = term->c_ispeed;
+
+  ct->ulClock = baud;
+  usart->bbr = usart_get_bbr(usart, pclk, baud);
+  return 0;
 }
 
 const console_fns stm32f4_usart_fns = {
   .deviceProbe = libchip_serial_default_probe,
   .deviceFirstOpen = usart_first_open,
   .deviceLastClose = usart_last_close,
+#ifdef BSP_CONSOLE_USE_INTERRUPTS
+  .deviceRead = NULL,
+#else
   .deviceRead = usart_read_polled,
+#endif
   .deviceWrite = usart_write_support_polled,
   .deviceInitialize = usart_initialize,
   .deviceWritePolled = usart_write_polled,