support quirk to reply to broadcast reads only.

Strict addressing bans replies to broadcast, and disabling it allows replies to all broadcast operations. This is helpful to find a single device of unknown address via broadcast reads. However, it's problematic when trying to use broadcast writes, where you do _not_ want to get a reply from each device. Defaults to off, for maximum out of the box compliance. define MB_QUIRK_REPLY_BROADCAST_READ 1 to enable this feature. Don't try and combine strict=0 and this quirk at the same time. Signed-off-by: Karl Palsson <[email protected]>
etactica · Jun 9, 2022 · 4ea6112 · 4ea6112
1 parent 5f6be12
commit 4ea6112
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diff --git a/modbus/include/mbconfig.h b/modbus/include/mbconfig.h
@@ -158,6 +158,14 @@ PR_BEGIN_EXTERN_C
 #define MB_STRICT_ADDRESSING			( 1 )
 #endif
 
+/*! \brief Quirk mode to allow replies to broadcast reads, but not writes.
+ * This is an alternative to relaxing MB_STRICT_ADDRESSING, which would
+ * also allow replies to broadcast writes.
+ */
+#ifndef MB_QUIRK_REPLY_BROADCAST_READ
+#define MB_QUIRK_REPLY_BROADCAST_READ           ( 0 )
+#endif
+
 /*! \brief provide a notification hook in the rx path.
  * Must provide a hook function of the form:
  * vMBPortNotifyRX(UCHAR *rxdata, USHORT length)

diff --git a/modbus/mb.c b/modbus/mb.c
@@ -391,6 +391,20 @@ eMBPoll( void )
             if( ucRcvAddress != MB_ADDRESS_BROADCAST )
             {
 #endif
+
+#if MB_QUIRK_REPLY_BROADCAST_READ > 0
+                    /*
+                     * reply to any non-broadcast, and also broadcasts for these
+                     * few functions used for discovering devices.
+                     */
+                    if (!(ucRcvAddress == MB_ADDRESS_BROADCAST) ||
+                            ((ucRcvAddress == MB_ADDRESS_BROADCAST) && (
+                                (ucFunctionCode == MB_FUNC_READ_INPUT_REGISTER) ||
+                                (ucFunctionCode == MB_FUNC_READ_HOLDING_REGISTER) ||
+                                (ucFunctionCode == MB_FUNC_OTHER_REPORT_SLAVEID))
+                            )) {
+#endif
+
                 if( eException != MB_EX_NONE )
                 {
                     /* An exception occured. Build an error frame. */
@@ -411,6 +425,10 @@ eMBPoll( void )
 #endif
                 /* Receive address == our address, or broadcast, if allowed */
                 eStatus = peMBFrameSendCur( ucRcvAddress, ucMBFrame, usLength );
+#if MB_QUIRK_REPLY_BROADCAST_READ > 0
+		}
+#endif
+
 #if MB_STRICT_ADDRESSING > 0
             }
 #endif