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From 1c5d969f46ccd5333f602dfbe2b0a1295650b9b0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?St=C3=A9phane=20Raimbault?= <stephane.raimbault@gmail.com>
Date: Wed, 25 Oct 2017 20:35:47 +0200
Subject: [PATCH 1/2] Only set SER_RS485_ENABLED bit of existing RS485 settings
Thanks to @JCWren
---
src/modbus-rtu.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index 8d9f386..f2911d6 100644
--- a/src/modbus-rtu.c
+++ b/src/modbus-rtu.c
@@ -909,9 +909,13 @@ int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode)
#if HAVE_DECL_TIOCSRS485
modbus_rtu_t *ctx_rtu = ctx->backend_data;
struct serial_rs485 rs485conf;
- memset(&rs485conf, 0x0, sizeof(struct serial_rs485));
if (mode == MODBUS_RTU_RS485) {
+ // Get
+ if (ioctl(ctx->s, TIOCGRS485, &rs485conf) < 0) {
+ return -1;
+ }
+ // Set
rs485conf.flags = SER_RS485_ENABLED;
if (ioctl(ctx->s, TIOCSRS485, &rs485conf) < 0) {
return -1;
@@ -923,6 +927,10 @@ int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode)
/* Turn off RS485 mode only if required */
if (ctx_rtu->serial_mode == MODBUS_RTU_RS485) {
/* The ioctl call is avoided because it can fail on some RS232 ports */
+ if (ioctl(ctx->s, TIOCGRS485, &rs485conf) < 0) {
+ return -1;
+ }
+ rs485conf.flags &= ~SER_RS485_ENABLED;
if (ioctl(ctx->s, TIOCSRS485, &rs485conf) < 0) {
return -1;
}
--
2.21.0