# HG changeset patch
# User bmakuc <blaz.makuc@smarteh.si>
# Date 1574862802 -3600
# Node ID 99009b24d4015f9f0ba74bb4c26a86fd009a9c0f
# Parent  1223f413e0540e15b7ac71fb0b6b90d7c3306e22
Variables start_addr and count were read from query_packet using function mb_ntoh_safe. It looks like some compilers change the pointer alignment if the first byte starts at an odd address. Because mb_ntoh_safe uses pointers slave address and count (number of registers) were not read correctly from the buffer when several modbus slaves were present in network. In this temporary solution pointer aritmetics is replaced by simple 256 multiplication.

diff -r 1223f413e054 -r 99009b24d401 mb_slave.c
--- a/mb_slave.c	Mon Feb 11 11:07:01 2019 +0100
+++ b/mb_slave.c	Wed Nov 27 14:53:22 2019 +0100
@@ -312,8 +312,10 @@
      *   requiring the user to use addressing starting off at 0! 
      */
   /* start_addr = mb_ntoh(u16_v(query_packet[2])) + 1; */
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
-  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+//  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
+  count = query_packet[4] * 256 + query_packet[5];      /* Temporary pointer alignment fix */
 
   #ifdef DEBUG
   printf("handle_read_input_bits() called. slave=%d, function=%d, start_addr=%d, count=%d\n", 
@@ -376,8 +378,10 @@
   resp_packet = *resp_packet_ptr;
   
   /* See equivalent comment in handle_read_bits() */ 
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
-  mb_ntoh_safe(u16_v(query_packet[4]), &count);
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+//  mb_ntoh_safe(u16_v(query_packet[4]), &count);
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
+  count = query_packet[4] * 256 + query_packet[5];      /* Temporary pointer alignment fix */
 
   #ifdef DEBUG
   printf("handle_read_output_words() called. slave=%d, function=%d, start_addr=%d, count=%d\n", 
@@ -432,7 +436,8 @@
   resp_packet = *resp_packet_ptr;
   
   /* See equivalent comment in handle_read_bits() */ 
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
 
   #ifdef DEBUG
   printf("handle_write_output_bit() called. slave=%d, function=%d, start_addr=%d\n", 
@@ -477,8 +482,9 @@
   resp_packet = *resp_packet_ptr;
   
   /* See equivalent comment in handle_read_bits() */ 
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
-  
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
+ 
   #ifdef DEBUG
   printf("handle_write_output_word() called. slave=%d, function=%d, start_addr=%d\n", 
          query_packet[0], query_packet[1], start_addr);
@@ -520,8 +526,10 @@
   resp_packet = *resp_packet_ptr;
   
   /* See equivalent comment in handle_read_bits() */ 
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
-  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+//  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
+  count = query_packet[4] * 256 + query_packet[5];      /* Temporary pointer alignment fix */
 
   #ifdef DEBUG
   printf("handle_write_output_bits() called. slave=%d, function=%d, start_addr=%d, count=%d\n", 
@@ -566,9 +574,11 @@
   resp_packet = *resp_packet_ptr;
   
   /* See equivalent comment in handle_read_bits() */ 
-  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
-  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
-  
+//  mb_ntoh_safe(u16_v(query_packet[2]), &start_addr);
+//  mb_ntoh_safe(u16_v(query_packet[4]), &count); 
+  start_addr = query_packet[2] * 256 + query_packet[3]; /* Temporary pointer alignment fix */
+  count = query_packet[4] * 256 + query_packet[5];      /* Temporary pointer alignment fix */
+
   if ((count > MAX_WRITE_REGS) || (count < 1) || (count*2 != query_packet[6]) )
     {*error_code = ERR_ILLEGAL_DATA_VALUE; return -1;}