[PATCH 1/2] Add modbus_read_input_registers() command to modbus plugin

The modbus plugin currently only does a modbus_read_registers()
call (modbus command 0x03).  Some devices have registers which
must be read with modbus_read_input_registers() (command 0x04).

This patch allows the config file to specify which command to
use; the default remains the same (modbus_read_registers) but
can be specified with:

    RegisterCmd ReadHolding
or
    RegisterCmd ReadInput

in each <Data> definition block.

I've tested this with newer libmodbus (v3.0+) but not the
legacy code.  Works great with my Triangle Tube boiler.

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---

diff --git a/src/modbus.c b/src/modbus.c
index 887c63c..b90266e 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -48,6 +48,7 @@
  * <Data "data_name">
  *   RegisterBase 1234
  *   RegisterType float
+ *   RegisterCmd ReadHolding # default, or: ReadInput
  *   Type gauge
  *   Instance "..."
  * </Data>
@@ -77,6 +78,12 @@ enum mb_register_type_e /* {{{ */
 }; /* }}} */
 typedef enum mb_register_type_e mb_register_type_t;
 
+enum mb_register_cmd_e /* {{{ */
+{
+  REG_CMD_READ_HOLDING,
+  REG_CMD_READ_INPUT
+}; /* }}} */
+typedef enum mb_register_cmd_e mb_register_cmd_t;
 struct mb_data_s;
 typedef struct mb_data_s mb_data_t;
 struct mb_data_s /* {{{ */
@@ -84,6 +91,7 @@ struct mb_data_s /* {{{ */
   char *name;
   int register_base;
   mb_register_type_t register_type;
+  mb_register_cmd_t register_cmd;
   char type[DATA_MAX_NAME_LEN];
   char instance[DATA_MAX_NAME_LEN];
 
@@ -457,6 +465,8 @@ static int mb_read_data (mb_host_t *host, mb_slave_t *slave, /* {{{ */
    * id to each call of "read_holding_registers". */
 # define modbus_read_registers(ctx, addr, nb, dest) \
   read_holding_registers (&(ctx), slave->id, (addr), (nb), (dest))
+# define modbus_read_input_registers(ctx, addr, nb, dest) \
+  read_input_registers (&(ctx), slave->id, (addr), (nb), (dest))
 #else /* if !LEGACY_LIBMODBUS */
   /* Version 2.9.2: Set the slave id once before querying the registers. */
   status = modbus_set_slave (host->connection, slave->id);
@@ -468,13 +478,20 @@ static int mb_read_data (mb_host_t *host, mb_slave_t *slave, /* {{{ */
   }
 #endif
 
-  status = modbus_read_registers (host->connection,
-        /* start_addr = */ data->register_base,
-        /* num_registers = */ values_num, /* buffer = */ values);
+  if (data->register_cmd == REG_CMD_READ_INPUT)
+    status = modbus_read_input_registers (host->connection,
+          /* start_addr = */ data->register_base,
+          /* num_registers = */ values_num, /* buffer = */ values);
+  else
+    status = modbus_read_registers (host->connection,
+          /* start_addr = */ data->register_base,
+          /* num_registers = */ values_num, /* buffer = */ values);
+
   if (status != values_num)
   {
-    ERROR ("Modbus plugin: modbus_read_registers (%s/%s) failed. status = %i, values_num = %i "
-        "Giving up.", host->host, host->node, status, values_num);
+    ERROR ("Modbus plugin: modbus_read_%sregisters (%s/%s) failed. status = %i, values_num = %i "
+        "Giving up.", data->register_cmd == REG_CMD_READ_INPUT ? "input_" : "",
+        host->host, host->node, status, values_num);
 #if LEGACY_LIBMODBUS
     modbus_close (&host->connection);
 #else
@@ -486,7 +503,8 @@ static int mb_read_data (mb_host_t *host, mb_slave_t *slave, /* {{{ */
   }
 
   DEBUG ("Modbus plugin: mb_read_data: Success! "
-      "modbus_read_registers returned with status %i.", status);
+      "modbus_read_%sregisters returned with status %i.",
+      data->register_cmd == REG_CMD_READ_INPUT ? "input_" : "", status);
 
   if (data->register_type == REG_TYPE_FLOAT)
   {
@@ -668,6 +686,7 @@ static int mb_config_add_data (oconfig_item_t *ci) /* {{{ */
   memset (&data, 0, sizeof (data));
   data.name = NULL;
   data.register_type = REG_TYPE_UINT16;
+  data.register_cmd = REG_CMD_READ_HOLDING;
   data.next = NULL;
 
   status = cf_util_get_string (ci, &data.name);
@@ -709,6 +728,22 @@ static int mb_config_add_data (oconfig_item_t *ci) /* {{{ */
         status = -1;
       }
     }
+    else if (strcasecmp ("RegisterCmd", child->key) == 0)
+    {
+      char tmp[16];
+      status = cf_util_get_string_buffer (child, tmp, sizeof (tmp));
+      if (status != 0)
+        /* do nothing */;
+      else if (strcasecmp ("ReadHolding", tmp) == 0)
+        data.register_cmd= REG_CMD_READ_HOLDING;
+      else if (strcasecmp ("ReadInput", tmp) == 0)
+        data.register_cmd = REG_CMD_READ_INPUT; 
+      else
+      {
+        ERROR ("Modbus plugin: The register command \"%s\" is unknown.", tmp);
+        status = -1;
+      }
+    }
     else
     {
       ERROR ("Modbus plugin: Unknown configuration option: %s", child->key);