[En-Nut-Discussion] UART Flow Control

[bon at elektron.ikp.physik.tu-darmstadt.de]

Dušan writes:
> Hi guys,
> 
> we are working on a Nut/OS port for NXP Kinetis MK64F (LQFP100 - 144, 
> ethernet).
> Actual state can be seen here: https://github.com/dferbas/ethernut
> 
> Once tested, I plan to merge it with Nut.
> It does not use the NutUseCritical() macros.
> 
> ------------------------
> We have an issue with USART driver.
> We use the UART_SETFLOWCONTROL to set half duplex or full duplex and 
> also loopback modes.
> All this is done with RE, DE signals to 2 RS485 transceivers, nicely 
> hidden from an application through the ioctl.
> 
> The [r4163] <https://sourceforge.net/p/ethernut/code/4163/> added 
> XONXOFF only, which was later removed at
>
> [r4584] <https://sourceforge.net/p/ethernut/code/4584/> with following 
> remark:
> Do not fix flow control to XON/XOFF handshake.
> See 
> http://lists.egnite.de/pipermail/en-nut-discussion/2012-August/013821.html
> 
> ---
> As the dcb->dcb_modeflags should be hidden from an application,
> what was the intention to leave it as it is now?
> 
> What about to simply stay with the old version (#2555 - #4116):
>      case UART_SETFLOWCONTROL:
>          rc = (*dcb->dcb_set_flow_control) (lv);
>          break;
> 
> This allows everything to be passed from an application.

I recently also implemented XON/XOFF for STM32 and have following
patch not yet pushed to sourceforge:
commit 60a551843e2dd5cb4846939d50b03aaf0d50ce4e
Author: Uwe Bonnes <bon at elektron.ikp.physik.tu-darmstadt.de>
Date:   Wed Feb 19 20:27:47 2020 +0100

    usart.c: We must relay XONXOFF to the dcb_modeflags.
    
    Only relay dcb_modeflags. See http://lists.egnite.de/pipermail/en-nut-discussion/2012-August/013821.html.

diff --git a/nut/dev/usart.c b/nut/dev/usart.c
index a8228ef87..008dd036d 100644
--- a/nut/dev/usart.c
+++ b/nut/dev/usart.c
@@ -834,6 +834,11 @@ int UsartIOCtl(NUTDEVICE * dev, int req, void *conf)
 
     case UART_SETFLOWCONTROL:
         lv = dcb->dcb_modeflags;
+        if (bv & USART_MF_XONXOFF) {
+            lv |= USART_MF_XONXOFF;
+        } else {
+            lv &= ~USART_MF_XONXOFF;
+        }
         rc = (dcb->dcb_set_flow_control) (lv);
         if (rc == 0) {
             dcb->dcb_modeflags = lv;

This only changes XONXOFF, but keeps other settings, e.g. half-duplex etc.

What do you think of my solution?

As neither Harald nor Ole seem to lurk, the original intention of the
modification is probably lost.

Should I put up my nutos repo on github?

Bye
-- 
Uwe Bonnes                bon at elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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