Modbus TCP - Multi Devices

main/modbus_tcp.h

@@ -0,0 +1,65 @@
+#ifndef MODBUS_TCP_H
+#define MODBUS_TCP_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+#include "modbus_memory.h"
+
+#define MODBUS_TCP_PORT 502
+
+/* MBAP header is always 7 bytes */
+#define MODBUS_TCP_MBAP_LEN 7
+
+/* Maximum Modbus TCP ADU size:
+ * 7-byte MBAP + up to 253-byte PDU = 260 bytes
+ */
+#define MODBUS_TCP_MAX_ADU_LEN 260
+#define MODBUS_TCP_MAX_PDU_LEN 253
+
+/* Modbus exception codes */
+#define MODBUS_EX_ILLEGAL_FUNCTION      0x01
+#define MODBUS_EX_ILLEGAL_DATA_ADDRESS  0x02
+#define MODBUS_EX_ILLEGAL_DATA_VALUE    0x03
+#define MODBUS_EX_SERVER_DEVICE_FAILURE 0x04
+
+/* Supported function codes */
+#define MODBUS_FC_READ_COILS               0x01
+#define MODBUS_FC_READ_DISCRETE_INPUTS     0x02
+#define MODBUS_FC_READ_HOLDING_REGISTERS   0x03
+#define MODBUS_FC_READ_INPUT_REGISTERS     0x04
+#define MODBUS_FC_WRITE_SINGLE_COIL        0x05
+#define MODBUS_FC_WRITE_SINGLE_REGISTER    0x06
+#define MODBUS_FC_WRITE_MULTIPLE_COILS     0x0F
+#define MODBUS_FC_WRITE_MULTIPLE_REGISTERS 0x10
+
+typedef struct
+{
+    uint16_t transaction_id;
+    uint16_t protocol_id;
+    uint16_t length;
+    uint8_t unit_id;
+} modbus_mbap_t;
+
+/*
+ * Process one Modbus TCP request ADU and write the response ADU.
+ *
+ * mem           = target virtual device memory
+ * req           = incoming request bytes
+ * req_len       = number of request bytes
+ * resp          = output response buffer
+ * resp_max_len  = size of resp buffer
+ * resp_len      = actual response length written
+ *
+ * Returns true if a response was built successfully.
+ * Returns false on malformed packet / buffer issues.
+ */
+bool modbus_tcp_process_request(modbus_memory_t *mem,
+                                const uint8_t *req,
+                                size_t req_len,
+                                uint8_t *resp,
+                                size_t resp_max_len,
+                                size_t *resp_len);
+
+#endif /* MODBUS_TCP_H */