Optimize slave address setting in mbpoll loop

google-labs-jules[bot] · zknpr · google-labs-jules[bot] · commit b37345e67c9c · 2026-02-07T13:06:50.000Z
Avoid calling `modbus_set_slave` if the slave address is already set to the desired value. This reduces redundant function calls during polling, improving efficiency.

The change introduces a check using `modbus_get_slave` before calling `modbus_set_slave`. The error handling logic is preserved.

Verified functionality and performance with a local Modbus TCP server. The behavior remains correct.

Co-authored-by: zknpr &lt;96851588+zknpr@users.noreply.github.com&gt;
diff --git a/src/mbpoll.c b/src/mbpoll.c
@@ -997,10 +997,12 @@ main (int argc, char **argv) {
         // Read -------------------------------------------------------------
         for (i = 0; i < ctx.iSlaveCount; i++) {
 
-          iRet = modbus_set_slave (ctx.xBus, ctx.piSlaveAddr[i]);
-          if (iRet != 0) {
-            vIoErrorExit ("Setting slave address failed: %s",
-                          modbus_strerror (errno));
+          if (modbus_get_slave (ctx.xBus) != ctx.piSlaveAddr[i]) {
+            iRet = modbus_set_slave (ctx.xBus, ctx.piSlaveAddr[i]);
+            if (iRet != 0) {
+              vIoErrorExit ("Setting slave address failed: %s",
+                            modbus_strerror (errno));
+            }
           }
           ctx.iTxCount++;
 
