From a00ab52931a587cf29c53a945e9295b4d7fe41ba Mon Sep 17 00:00:00 2001
From: Daniel Golle <daniel@makrotopia.org>
Date: Thu, 28 Mar 2019 01:52:04 +0100
Subject: [PATCH] Add support for RS485 to modbus plugin

Allow setting up RS485 mode for Modbus-RTU
---
 src/collectd.conf.pod |  6 ++++++
 src/modbus.c          | 55 +++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 57 insertions(+), 4 deletions(-)

diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index 5efc8cb7..0cc9a7c8 100644
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -4453,6 +4453,12 @@ For Modbus/RTU, specifies the path to the serial device being used.
 For Modbus/RTU, specifies the baud rate of the serial device.
 Note, connections currently support only 8/N/1.
 
+=item B<UARTType> I<UARTType>
+
+For Modbus/RTU, specifies the type of the serial device.
+RS232, RS422 and RS485 are supported. Defaults to RS232.
+Available only on Linux systems with libmodbus>=2.9.4.
+
 =item B<Interval> I<Interval>
 
 Sets the interval (in seconds) in which the values will be collected from this
diff --git a/src/modbus.c b/src/modbus.c
index ed53319f..04232c35 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -97,6 +97,12 @@ enum mb_conntype_e /* {{{ */
   MBCONN_RTU }; /* }}} */
 typedef enum mb_conntype_e mb_conntype_t;
 
+enum mb_uarttype_e /* {{{ */
+{ UARTTYPE_RS232,
+  UARTTYPE_RS422,
+  UARTTYPE_RS485 }; /* }}} */
+typedef enum mb_uarttype_e mb_uarttype_t;
+
 struct mb_data_s;
 typedef struct mb_data_s mb_data_t;
 struct mb_data_s /* {{{ */
@@ -126,8 +132,9 @@ struct mb_host_s /* {{{ */
   char host[DATA_MAX_NAME_LEN];
   char node[NI_MAXHOST]; /* TCP hostname or RTU serial device */
   /* char service[NI_MAXSERV]; */
-  int port;     /* for Modbus/TCP */
-  int baudrate; /* for Modbus/RTU */
+  int port;               /* for Modbus/TCP */
+  int baudrate;           /* for Modbus/RTU */
+  mb_uarttype_t uarttype; /* UART type for Modbus/RTU */
   mb_conntype_t conntype;
 
   mb_slave_t *slaves;
@@ -387,6 +394,22 @@ static int mb_init_connection(mb_host_t *host) /* {{{ */
     return status;
   }
 
+#if defined(linux) && LIBMODBUS_VERSION_CHECK(2, 9, 4)
+  switch (host->uarttype) {
+  case UARTTYPE_RS485:
+    if (modbus_rtu_set_serial_mode(host->connection, MODBUS_RTU_RS485))
+      DEBUG("Modbus plugin: Setting RS485 mode failed.");
+    break;
+  case UARTTYPE_RS422:
+    /* libmodbus doesn't say anything about full-duplex symmetric RS422 UART */
+    break;
+  case UARTTYPE_RS232:
+    break;
+  default:
+    DEBUG("Modbus plugin: Invalid UART type!.");
+  }
+#endif /* defined(linux) && LIBMODBUS_VERSION_CHECK(2, 9, 4) */
+
   return 0;
 } /* }}} int mb_init_connection */
 #endif /* !LEGACY_LIBMODBUS */
@@ -983,11 +1006,35 @@ static int mb_config_add_host(oconfig_item_t *ci) /* {{{ */
         status = -1;
     } else if (strcasecmp("Device", child->key) == 0) {
       status = cf_util_get_string_buffer(child, host->node, sizeof(host->node));
-      if (status == 0)
+      if (status == 0) {
         host->conntype = MBCONN_RTU;
+        host->uarttype = UARTTYPE_RS232;
+      }
     } else if (strcasecmp("Baudrate", child->key) == 0)
       status = cf_util_get_int(child, &host->baudrate);
-    else if (strcasecmp("Interval", child->key) == 0)
+    else if (strcasecmp("UARTType", child->key) == 0) {
+#if defined(linux) && !LEGACY_LIBMODBUS && LIBMODBUS_VERSION_CHECK(2, 9, 4)
+      char buffer[NI_MAXHOST];
+      status = cf_util_get_string_buffer(child, buffer, sizeof(buffer));
+      if (status != 0)
+        break;
+      if (strncmp(buffer, "RS485", 6) == 0)
+        host->uarttype = UARTTYPE_RS485;
+      else if (strncmp(buffer, "RS422", 6) == 0)
+        host->uarttype = UARTTYPE_RS422;
+      else if (strncmp(buffer, "RS232", 6) == 0)
+        host->uarttype = UARTTYPE_RS232;
+      else {
+        ERROR("Modbus plugin: The UARTType \"%s\" is unknown.", buffer);
+        status = -1;
+        break;
+      }
+#else
+      ERROR("Modbus plugin: Option `UARTType' not supported. Please "
+            "upgrade libmodbus to at least 2.9.4");
+      return -1;
+#endif
+    } else if (strcasecmp("Interval", child->key) == 0)
       status = cf_util_get_cdtime(child, &interval);
     else if (strcasecmp("Slave", child->key) == 0)
       /* Don't set status: Gracefully continue if a slave fails. */
-- 
2.11.0