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commit 444073e37047832c0dc9dbe3678b0dd9b82d1689
Author: Jiri Vlasak <[email protected]>
AuthorDate: Wed Mar 25 12:04:40 2026 +0100

    kinetis/serial: Do not xmit when no chars to xmit
    
    When there are no data in the TX buffer, we can avoid call to the
    uart_xmitchars.
    
    Signed-off-by: Jiri Vlasak <[email protected]>
---
 arch/arm/src/kinetis/kinetis_serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/src/kinetis/kinetis_serial.c 
b/arch/arm/src/kinetis/kinetis_serial.c
index 232f0999aa9..ddffc8130c0 100644
--- a/arch/arm/src/kinetis/kinetis_serial.c
+++ b/arch/arm/src/kinetis/kinetis_serial.c
@@ -1288,7 +1288,7 @@ static int up_interrupts(int irq, void *context, void 
*arg)
        * the TX data register.
        */
 
-      if ((s1 & UART_S1_TDRE) != 0)
+      if ((s1 & UART_S1_TDRE) != 0 && dev->xmit.head != dev->xmit.tail)
 #endif
         {
           /* Process outgoing bytes */

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