bsp/atsam: Improve UART / USART tx performance

Put the next character into the send buffer if the buffer is empty and
not when the last character has been sent out to the line. This improves
the performance slightly.

Before that patch, the receive path was faster than the transmit path.
Therefore a simple echo could drop characters on a busy connection.
With this patch sending and receiving has about the same performance so
that no characters are lost.

Fixes #4610

1 files changed, 5 insertions, 4 deletions

diff --git a/bsps/arm/atsam/console/console.c b/bsps/arm/atsam/console/console.c
index 5ef4327e11..0802ca2155 100644
--- a/bsps/arm/atsam/console/console.c
+++ b/bsps/arm/atsam/console/console.c
@@ -145,8 +145,9 @@ static void atsam_uart_interrupt(void *arg)
     }
   }
 
-  if (ctx->transmitting && (sr & UART_SR_TXEMPTY) != 0) {
+  while (ctx->transmitting && (sr & UART_SR_TXRDY) != 0) {
     rtems_termios_dequeue_characters(tty, 1);
+    sr = regs->UART_SR;
   }
 }
 #endif
@@ -408,16 +409,16 @@ static void atsam_uart_write(
   if (len > 0) {
     ctx->transmitting = true;
     regs->UART_THR = buf[0];
-    regs->UART_IER = UART_IDR_TXEMPTY;
+    regs->UART_IER = UART_IDR_TXRDY;
   } else {
     ctx->transmitting = false;
-    regs->UART_IDR = UART_IDR_TXEMPTY;
+    regs->UART_IDR = UART_IDR_TXRDY;
   }
 #else
   size_t i;
 
   for (i = 0; i < len; ++i) {
-    while ((regs->UART_SR & UART_SR_TXEMPTY) == 0) {
+    while ((regs->UART_SR & UART_SR_TXRDY) == 0) {
       /* Wait */
     }