Adding upstream version 4.2.2.upstream/4.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1013 insertions, 0 deletions

diff --git a/epan/dissectors/packet-mdb.c b/epan/dissectors/packet-mdb.c
new file mode 100644
index 00000000..6c16ea4c
--- /dev/null
+++ b/epan/dissectors/packet-mdb.c
@@ -0,0 +1,1013 @@
+/*
+ * packet-mdb.c
+ * Routines for MDB dissection
+ * Copyright 2023 Martin Kaiser for PayTec AG (www.paytec.ch)
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+/*
+ * The MDB (Multi-Drop Bus) protocol is used inside a vending machine. MDB
+ * defines the communication between the main control board (VMC = Vending
+ * Machine Controller) and peripheral components, e.g. a payment terminal
+ * or a bill validator.
+ *
+ * The VMC acts as bus master and sends a request to one peripheral at a time.
+ * A peripheral may send data only in response to such a request.
+ *
+ * The MDB specification is maintained by the National Automatic Merchandising
+ * Association (NAMA). As of August 2023, the current version of the MDB
+ * specification is 4.3. It is available from
+ * https://namanow.org/nama-releases-mdb-version-4-3/
+ *
+ * The pcap input format for this dissector is documented at
+ * https://www.kaiser.cx/pcap-mdb.html
+ */
+
+#include "config.h"
+#include <epan/expert.h>
+#include <epan/packet.h>
+#include <wiretap/wtap.h>
+
+void proto_register_mdb(void);
+
+static dissector_handle_t mdb_handle;
+
+static int proto_mdb = -1;
+
+static int ett_mdb = -1;
+static int ett_mdb_hdr = -1;
+static int ett_mdb_cl = -1;
+static int ett_mdb_cgw = -1;
+
+static int hf_mdb_hdr_ver = -1;
+static int hf_mdb_event = -1;
+static int hf_mdb_addr = -1;
+static int hf_mdb_cmd = -1;
+static int hf_mdb_cl_setup_sub = -1;
+static int hf_mdb_cl_feat_lvl = -1;
+static int hf_mdb_cl_cols = -1;
+static int hf_mdb_cl_rows = -1;
+static int hf_mdb_cl_disp_info = -1;
+static int hf_mdb_cl_max_price = -1;
+static int hf_mdb_cl_min_price = -1;
+static int hf_mdb_cl_vend_sub = -1;
+static int hf_mdb_cl_item_price = -1;
+static int hf_mdb_cl_item_num = -1;
+static int hf_mdb_cl_reader_sub = -1;
+static int hf_mdb_cl_resp = -1;
+static int hf_mdb_cl_scale = -1;
+static int hf_mdb_cl_dec_pl = -1;
+static int hf_mdb_cl_max_rsp_time = -1;
+static int hf_mdb_cl_vend_amt = -1;
+static int hf_mdb_cl_expns_sub = -1;
+static int hf_mdb_cl_manuf_code = -1;
+static int hf_mdb_cl_ser_num = -1;
+static int hf_mdb_cl_mod_num = -1;
+static int hf_mdb_cl_opt_feat = -1;
+static int hf_mdb_cgw_feat_lvl = -1;
+static int hf_mdb_cgw_scale = -1;
+static int hf_mdb_cgw_dec_pl = -1;
+static int hf_mdb_cgw_resp = -1;
+static int hf_mdb_cgw_max_rsp_time = -1;
+static int hf_mdb_cgw_report_sub = -1;
+static int hf_mdb_cgw_dts_evt_code = -1;
+static int hf_mdb_cgw_duration = -1;
+static int hf_mdb_cgw_activity = -1;
+static int hf_mdb_cgw_expns_sub = -1;
+static int hf_mdb_cgw_opt_feat = -1;
+static int hf_mdb_cgw_manuf_code = -1;
+static int hf_mdb_cgw_ser_num = -1;
+static int hf_mdb_cgw_mod_num = -1;
+static int hf_mdb_ack = -1;
+static int hf_mdb_data = -1;
+static int hf_mdb_chk = -1;
+
+static expert_field ei_mdb_short_packet = EI_INIT;
+
+#define MDB_EVT_DATA_MST_PER 0xFF
+#define MDB_EVT_DATA_PER_MST 0xFE
+#define MDB_EVT_BUS_RESET    0xFD
+
+static const value_string mdb_event[] = {
+    { MDB_EVT_DATA_MST_PER, "Data transfer Master -> Peripheral" },
+    { MDB_EVT_DATA_PER_MST, "Data transfer Peripheral -> Master" },
+    { MDB_EVT_BUS_RESET, "Bus reset" },
+    { 0, NULL }
+};
+
+#define ADDR_VMC "VMC"
+
+#define ADDR_CASHLESS1 0x10
+#define ADDR_COMMS_GW  0x18
+
+static const value_string mdb_addr[] = {
+    { 0x08, "Changer" },
+    { ADDR_CASHLESS1, "Cashless #1" },
+    { ADDR_COMMS_GW, "Communications Gateway" },
+    { 0x30, "Bill Validator" },
+    { 0x60, "Cashless #2" },
+    { 0x68, "Age Verification Device" },
+    { 0, NULL }
+};
+
+static const value_string mdb_ack[] = {
+    { 0x00, "ACK" },
+    { 0xAA, "RET" },
+    { 0xFF, "NAK" },
+    { 0, NULL }
+};
+
+/*
+ * These are just the command bits in the address + command byte. MDB supports
+ * two Cashless peripherals (Cashless #1 and #2) with different addresses,
+ * both use the same commands.
+ */
+#define MDB_CL_CMD_SETUP  0x01
+#define MDB_CL_CMD_VEND   0x03
+#define MDB_CL_CMD_READER 0x04
+#define MDB_CL_CMD_EXPNS  0x07
+
+static const value_string mdb_cl_cmd[] = {
+    { 0x00, "Reset" },
+    { MDB_CL_CMD_SETUP, "Setup" },
+    { 0x02, "Poll" },
+    { MDB_CL_CMD_VEND, "Vend" },
+    { MDB_CL_CMD_READER, "Reader" },
+    { MDB_CL_CMD_EXPNS, "Expansion" },
+    { 0, NULL }
+};
+
+#define MDB_CL_SETUP_CFG_DATA 0x00
+#define MDB_CL_SETUP_MAX_MIN  0x01
+
+static const value_string mdb_cl_setup_sub_cmd[] = {
+    { MDB_CL_SETUP_CFG_DATA, "Config Data" },
+    { MDB_CL_SETUP_MAX_MIN, "Max/Min Prices" },
+    { 0, NULL }
+};
+
+#define MDB_CL_VEND_REQ 0x00
+#define MDB_CL_VEND_SUC 0x02
+
+static const value_string mdb_cl_vend_sub_cmd[] = {
+    { MDB_CL_VEND_REQ, "Vend Request" },
+    { MDB_CL_VEND_SUC, "Vend Success" },
+    { 0x04, "Session Complete" },
+    { 0, NULL }
+};
+
+static const value_string mdb_cl_reader_sub_cmd[] = {
+    { 0x00, "Reader Disable" },
+    { 0x01, "Reader Enable" },
+    { 0, NULL }
+};
+
+#define MDB_CL_EXPNS_REQ_ID  0x00
+#define MDB_CL_EXPNS_OPT_ENA 0x04
+
+static const value_string mdb_cl_expns_sub_cmd[] = {
+    { MDB_CL_EXPNS_REQ_ID, "Request ID" },
+    { MDB_CL_EXPNS_OPT_ENA, "Optional Feature Enabled" },
+    { 0, NULL }
+};
+
+#define MDB_CL_RESP_RD_CFG_DATA 0x01
+#define MDB_CL_RESP_VEND_APRV   0x05
+#define MDB_CL_RESP_PER_ID      0x09
+
+static const value_string mdb_cl_resp[] = {
+    { 0x00, "Just Reset" },
+    { MDB_CL_RESP_RD_CFG_DATA, "Reader Config Data" },
+    { 0x03, "Begin Session" },
+    { MDB_CL_RESP_VEND_APRV, "Vend Approved" },
+    { 0x06, "Vend Denied" },
+    { 0x07, "End Session" },
+    { MDB_CL_RESP_PER_ID, "Peripheral ID" },
+    { 0x0b, "Cmd Out Of Sequence" },
+    { 0, NULL }
+};
+
+/*
+ * For the Communications Gateway, we use the complete address + command byte
+ * as value for the value string. The values here match those in the MDB
+ * specification.
+ *
+ * There's only one Communications Gateway, the address bits are always the
+ * same. (This is different from the Cashless peripherals, see above.)
+ */
+#define MDB_CGW_ADDR_CMD_SETUP  0x19
+#define MDB_CGW_ADDR_CMD_REPORT 0x1B
+#define MDB_CGW_ADDR_CMD_EXPNS  0x1F
+
+static const value_string mdb_cgw_addr_cmd[] = {
+    { 0x18, "Reset" },
+    { MDB_CGW_ADDR_CMD_SETUP, "Setup" },
+    { 0x1A, "Poll" },
+    { MDB_CGW_ADDR_CMD_REPORT, "Report" },
+    { MDB_CGW_ADDR_CMD_EXPNS, "Expansion" },
+    { 0, NULL }
+};
+
+#define MDB_CGW_REPORT_DTS_EVT 0x02
+
+static const value_string mdb_cgw_report_sub_cmd[] = {
+    { 0x01, "Transaction" },
+    { MDB_CGW_REPORT_DTS_EVT, "DTS Event" },
+    { 0, NULL }
+};
+
+#define MDB_CGW_EXPNS_FEAT_ENA 0x01
+
+static const value_string mdb_cgw_expns_sub_cmd[] = {
+    { 0x00, "Identification" },
+    { MDB_CGW_EXPNS_FEAT_ENA, "Feature enable" },
+    { 0x02, "Time/Date Request" },
+    { 0, NULL }
+};
+
+#define MDB_CGW_RESP_CFG    0x01
+#define MDB_CGW_RESP_PER_ID 0x06
+
+static const value_string mdb_cgw_resp[] = {
+    { 0x00, "Just Reset" },
+    { MDB_CGW_RESP_CFG, "Comms Gateway Config" },
+    { 0x05, "DTS Event Acknowledge" },
+    { MDB_CGW_RESP_PER_ID, "Peripheral ID" },
+    { 0, NULL }
+};
+
+static void dissect_mdb_ack(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo, proto_tree *tree)
+{
+    guint32 ack;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_ack, tvb, offset, 1,
+                ENC_BIG_ENDIAN, &ack);
+    col_set_str(pinfo->cinfo, COL_INFO,
+            val_to_str_const(ack, mdb_ack, "Invalid ack byte"));
+}
+
+static void mdb_set_addrs(guint8 event, guint8 addr, packet_info *pinfo)
+{
+    const char *periph = val_to_str(addr, mdb_addr, "Unknown (0x%02x)");
+
+    /* pinfo->p2p_dir is from the perspective of the master (VMC) */
+
+    if (event == MDB_EVT_DATA_MST_PER) {
+        set_address(&pinfo->src, AT_STRINGZ, (int)strlen(ADDR_VMC)+1, ADDR_VMC);
+        set_address(&pinfo->dst, AT_STRINGZ, (int)strlen(periph)+1, periph);
+        pinfo->p2p_dir = P2P_DIR_SENT;
+    }
+    else if (event == MDB_EVT_DATA_PER_MST) {
+        set_address(&pinfo->src, AT_STRINGZ, (int)strlen(periph)+1, periph);
+        set_address(&pinfo->dst, AT_STRINGZ, (int)strlen(ADDR_VMC)+1, ADDR_VMC);
+        pinfo->p2p_dir = P2P_DIR_RECV;
+    }
+}
+
+static void dissect_mdb_cl_setup(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo, proto_tree *tree)
+{
+    guint32 sub_cmd, price;
+    const gchar *s;
+    proto_item *pi;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_cl_setup_sub,
+                    tvb, offset, 1, ENC_BIG_ENDIAN, &sub_cmd);
+    s = try_val_to_str(sub_cmd, mdb_cl_setup_sub_cmd);
+    if (s) {
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+    }
+    offset++;
+
+    switch (sub_cmd) {
+        case MDB_CL_SETUP_CFG_DATA:
+            proto_tree_add_item(tree, hf_mdb_cl_feat_lvl, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(tree, hf_mdb_cl_cols, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(tree, hf_mdb_cl_rows, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(tree, hf_mdb_cl_disp_info, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            break;
+
+        case MDB_CL_SETUP_MAX_MIN:
+            if (tvb_reported_length_remaining(tvb, offset) == 5) {
+                /* This is the "default version" of Max/Min Prices. */
+
+                /* XXX - convert the scaled prices into actual amounts */
+                price = tvb_get_ntohs(tvb, offset);
+                pi = proto_tree_add_uint_format(tree, hf_mdb_cl_max_price,
+                        tvb, offset, 2, price, "Maximum price: 0x%04x", price);
+                if (price == 0xFFFF) {
+                    proto_item_append_text(pi, " (unknown)");
+                }
+                offset += 2;
+
+                price = tvb_get_ntohs(tvb, offset);
+                pi = proto_tree_add_uint_format(tree, hf_mdb_cl_min_price,
+                        tvb, offset, 2, price, "Minimum price: 0x%04x", price);
+                if (price == 0x0000) {
+                    proto_item_append_text(pi, " (unknown)");
+                }
+            }
+            else if (tvb_reported_length_remaining(tvb, offset) == 11) {
+                /* This is the "expanded currency version" of Max/Min Prices. */
+
+                proto_tree_add_item(tree, hf_mdb_cl_max_price, tvb, offset, 4,
+                        ENC_BIG_ENDIAN);
+                offset += 4;
+                proto_tree_add_item(tree, hf_mdb_cl_min_price, tvb, offset, 4,
+                        ENC_BIG_ENDIAN);
+            }
+            /* XXX - expert info for other lengths */
+            break;
+    }
+}
+
+static void dissect_mdb_cl_vend(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo, proto_tree *tree)
+{
+    guint32 sub_cmd, price, item;
+    const gchar *s;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_cl_vend_sub, tvb, offset, 1,
+            ENC_BIG_ENDIAN, &sub_cmd);
+    s = try_val_to_str(sub_cmd, mdb_cl_vend_sub_cmd);
+    if (s) {
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+    }
+    offset++;
+
+    switch (sub_cmd) {
+        case MDB_CL_VEND_REQ:
+            if (tvb_reported_length_remaining(tvb, offset) == 5) {
+                proto_tree_add_item_ret_uint(tree, hf_mdb_cl_item_price, tvb,
+                        offset, 2, ENC_BIG_ENDIAN, &price);
+                offset += 2;
+                proto_tree_add_item_ret_uint(tree, hf_mdb_cl_item_num, tvb,
+                        offset, 2, ENC_BIG_ENDIAN, &item);
+                col_append_fstr(pinfo->cinfo, COL_INFO, " (item %d, price %d)",
+                        item, price);
+            }
+            /* XXX - dissect the longer request in Expanded Currency Mode */
+            break;
+        case MDB_CL_VEND_SUC:
+                proto_tree_add_item(tree, hf_mdb_cl_item_num, tvb, offset, 2,
+                        ENC_BIG_ENDIAN);
+            break;
+    }
+}
+
+static gint
+dissect_mdb_cl_id_fields(tvbuff_t *tvb, gint offset, proto_tree *tree)
+{
+    proto_tree_add_item(tree, hf_mdb_cl_manuf_code, tvb, offset, 3, ENC_ASCII);
+    offset += 3;
+    proto_tree_add_item(tree, hf_mdb_cl_ser_num, tvb, offset, 12, ENC_ASCII);
+    offset += 12;
+    proto_tree_add_item(tree, hf_mdb_cl_mod_num, tvb, offset, 12, ENC_ASCII);
+    offset += 12;
+    /* XXX - dissect the Software Version bytes */
+    offset += 2;
+
+    return offset;
+}
+
+static void dissect_mdb_cl_expns(tvbuff_t *tvb, gint offset, packet_info *pinfo,
+        proto_tree *tree)
+{
+    guint32 sub_cmd;
+    const gchar *s;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_cl_expns_sub,
+                    tvb, offset, 1, ENC_BIG_ENDIAN, &sub_cmd);
+    s = try_val_to_str(sub_cmd, mdb_cl_expns_sub_cmd);
+    if (s) {
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+    }
+    offset++;
+
+    switch (sub_cmd) {
+        case MDB_CL_EXPNS_REQ_ID:
+            dissect_mdb_cl_id_fields(tvb, offset, tree);
+            break;
+        case MDB_CL_EXPNS_OPT_ENA:
+            /* XXX - add a bitmask for the Optional Feature Bits */
+            proto_tree_add_item(tree, hf_mdb_cl_opt_feat, tvb, offset, 4,
+                    ENC_BIG_ENDIAN);
+            break;
+    }
+}
+
+static void dissect_mdb_cl_rd_cfg_data(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo _U_, proto_tree *tree)
+{
+    proto_tree_add_item(tree, hf_mdb_cl_feat_lvl, tvb, offset, 1,
+            ENC_BIG_ENDIAN);
+    offset++;
+    /* XXX - dissect Country/Currency Code */
+    offset += 2;
+    proto_tree_add_item(tree, hf_mdb_cl_scale, tvb, offset, 1, ENC_BIG_ENDIAN);
+    offset++;
+    proto_tree_add_item(tree, hf_mdb_cl_dec_pl, tvb, offset, 1, ENC_BIG_ENDIAN);
+    offset++;
+    proto_tree_add_item(tree, hf_mdb_cl_max_rsp_time, tvb, offset, 1,
+            ENC_TIME_SECS | ENC_BIG_ENDIAN);
+}
+
+static void dissect_mdb_mst_per_cl( tvbuff_t *tvb, gint offset, gint len _U_,
+        packet_info *pinfo, proto_tree *tree, proto_item *cmd_it,
+        guint8 addr_byte)
+{
+    guint8 cmd = addr_byte & 0x07; /* the 3-bit command */
+    proto_tree *cl_tree;
+    guint32 sub_cmd;
+    const gchar *s;
+
+    s = val_to_str_const(cmd, mdb_cl_cmd, "Unknown");
+    proto_item_append_text(cmd_it, " (%s)", s);
+    col_set_str(pinfo->cinfo, COL_INFO, s);
+
+    cl_tree = proto_tree_add_subtree(tree, tvb, offset, len, ett_mdb_cl,
+            NULL, "Cashless");
+
+    s = NULL;
+    switch (cmd) {
+        case MDB_CL_CMD_SETUP:
+            dissect_mdb_cl_setup(tvb, offset, pinfo, cl_tree);
+            break;
+        case MDB_CL_CMD_VEND:
+            dissect_mdb_cl_vend(tvb, offset, pinfo, cl_tree);
+            break;
+        case MDB_CL_CMD_READER:
+            proto_tree_add_item_ret_uint(cl_tree, hf_mdb_cl_reader_sub,
+                    tvb, offset, 1, ENC_BIG_ENDIAN, &sub_cmd);
+            s = try_val_to_str(sub_cmd, mdb_cl_reader_sub_cmd);
+            break;
+        case MDB_CL_CMD_EXPNS:
+            dissect_mdb_cl_expns(tvb, offset, pinfo, cl_tree);
+            break;
+    }
+    if (s)
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+}
+
+static void dissect_mdb_per_mst_cl( tvbuff_t *tvb, gint offset,
+        gint len _U_, packet_info *pinfo, proto_tree *tree)
+{
+    proto_tree *cl_tree;
+    guint32 cl_resp;
+
+    cl_tree = proto_tree_add_subtree(tree, tvb, offset, len, ett_mdb_cl,
+            NULL, "Cashless");
+
+    proto_tree_add_item_ret_uint(cl_tree, hf_mdb_cl_resp, tvb, offset, 1,
+            ENC_BIG_ENDIAN, &cl_resp);
+    col_set_str(pinfo->cinfo,
+            COL_INFO, val_to_str_const(cl_resp, mdb_cl_resp, "Unknown"));
+    offset++;
+
+    switch (cl_resp) {
+        case MDB_CL_RESP_RD_CFG_DATA:
+            dissect_mdb_cl_rd_cfg_data(tvb, offset, pinfo, cl_tree);
+            break;
+        case MDB_CL_RESP_VEND_APRV:
+            if (tvb_reported_length_remaining(tvb, offset) == 3) {
+                proto_tree_add_item(cl_tree, hf_mdb_cl_vend_amt, tvb, offset,
+                        2, ENC_BIG_ENDIAN);
+            }
+            /* XXX - dissect the longer response in Expanded Currency Mode */
+            break;
+        case MDB_CL_RESP_PER_ID:
+            dissect_mdb_cl_id_fields(tvb, offset, tree);
+            /* XXX - check if we have Optional Feature Bits */
+            break;
+    }
+}
+
+static void dissect_mdb_cgw_report(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo, proto_tree *tree)
+{
+    guint32 sub_cmd;
+    const gchar *s;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_cgw_report_sub,
+                    tvb, offset, 1, ENC_BIG_ENDIAN, &sub_cmd);
+    s = try_val_to_str(sub_cmd, mdb_cgw_report_sub_cmd);
+    if (s) {
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+    }
+    offset++;
+
+    switch (sub_cmd) {
+        case MDB_CGW_REPORT_DTS_EVT:
+            proto_tree_add_item(tree, hf_mdb_cgw_dts_evt_code, tvb, offset, 10,
+                    ENC_ASCII);
+            offset += 10;
+            /* XXX - dissect Date */
+            offset += 4;
+            /* XXX - dissect Time */
+            offset += 2;
+            proto_tree_add_item(tree, hf_mdb_cgw_duration, tvb, offset, 4,
+                    ENC_BIG_ENDIAN);
+            offset += 4;
+            proto_tree_add_item(tree, hf_mdb_cgw_activity, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            break;
+    }
+}
+
+static void dissect_mdb_cgw_expns(tvbuff_t *tvb, gint offset,
+        packet_info *pinfo, proto_tree *tree)
+{
+    guint32 sub_cmd;
+    const gchar *s;
+
+    proto_tree_add_item_ret_uint(tree, hf_mdb_cgw_expns_sub,
+                    tvb, offset, 1, ENC_BIG_ENDIAN, &sub_cmd);
+    s = try_val_to_str(sub_cmd, mdb_cgw_expns_sub_cmd);
+    if (s) {
+        col_set_str(pinfo->cinfo, COL_INFO, s);
+    }
+    offset++;
+
+    switch (sub_cmd) {
+        case MDB_CGW_EXPNS_FEAT_ENA:
+            proto_tree_add_item(tree, hf_mdb_cgw_opt_feat, tvb, offset, 4,
+                    ENC_BIG_ENDIAN);
+            break;
+    }
+}
+
+static void dissect_mdb_mst_per_cgw( tvbuff_t *tvb, gint offset, gint len,
+        packet_info *pinfo, proto_tree *tree, proto_item *cmd_it,
+        guint8 addr_cmd_byte)
+{
+    proto_tree *cgw_tree;
+    const gchar *s;
+
+    s = val_to_str_const(addr_cmd_byte, mdb_cgw_addr_cmd, "Unknown");
+    proto_item_append_text(cmd_it, " (%s)", s);
+    col_set_str(pinfo->cinfo, COL_INFO, s);
+
+    cgw_tree = proto_tree_add_subtree(tree, tvb, offset, len, ett_mdb_cgw,
+            NULL, "Communications Gateway");
+
+    switch (addr_cmd_byte) {
+        case MDB_CGW_ADDR_CMD_SETUP:
+            proto_tree_add_item(cgw_tree, hf_mdb_cgw_feat_lvl, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(cgw_tree, hf_mdb_cgw_scale, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(cgw_tree, hf_mdb_cgw_dec_pl, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            break;
+        case MDB_CGW_ADDR_CMD_REPORT:
+            dissect_mdb_cgw_report(tvb, offset, pinfo, cgw_tree);
+            break;
+        case MDB_CGW_ADDR_CMD_EXPNS:
+            dissect_mdb_cgw_expns(tvb, offset, pinfo, cgw_tree);
+            break;
+    }
+}
+
+static void dissect_mdb_per_mst_cgw( tvbuff_t *tvb, gint offset,
+        gint len, packet_info *pinfo _U_, proto_tree *tree)
+{
+    proto_tree *cgw_tree;
+    guint32 cgw_resp;
+
+    cgw_tree = proto_tree_add_subtree(tree, tvb, offset, len, ett_mdb_cgw,
+            NULL, "Communications Gateway");
+
+    proto_tree_add_item_ret_uint(cgw_tree, hf_mdb_cgw_resp, tvb, offset, 1,
+            ENC_BIG_ENDIAN, &cgw_resp);
+    col_set_str(pinfo->cinfo,
+            COL_INFO, val_to_str_const(cgw_resp, mdb_cgw_resp, "Unknown"));
+    offset++;
+
+    switch (cgw_resp) {
+        case MDB_CGW_RESP_CFG:
+            proto_tree_add_item(cgw_tree, hf_mdb_cgw_feat_lvl, tvb, offset, 1,
+                    ENC_BIG_ENDIAN);
+            offset++;
+            proto_tree_add_item(cgw_tree, hf_mdb_cgw_max_rsp_time, tvb, offset,
+                    2, ENC_TIME_SECS | ENC_BIG_ENDIAN);
+            break;
+        case MDB_CGW_RESP_PER_ID:
+            proto_tree_add_item(tree, hf_mdb_cgw_manuf_code, tvb, offset, 3,
+                    ENC_ASCII);
+            offset += 3;
+            proto_tree_add_item(tree, hf_mdb_cgw_ser_num, tvb, offset, 12,
+                    ENC_ASCII);
+            offset += 12;
+            proto_tree_add_item(tree, hf_mdb_cgw_mod_num, tvb, offset, 12,
+                    ENC_ASCII);
+            offset += 12;
+            /* XXX - dissect the Software Version bytes */
+            offset += 2;
+            proto_tree_add_item(tree, hf_mdb_cgw_opt_feat, tvb, offset, 4,
+                    ENC_BIG_ENDIAN);
+            break;
+    }
+}
+
+static void dissect_mdb_mst_per(tvbuff_t *tvb, gint offset, packet_info *pinfo,
+        proto_tree *tree)
+{
+    guint8 addr_byte, addr;
+    gint mst_per_len;
+    guint data_len;
+    proto_item *cmd_it;
+
+    mst_per_len = tvb_reported_length_remaining(tvb, offset);
+    if (mst_per_len <= 0) {
+        expert_add_info(pinfo, tree, &ei_mdb_short_packet);
+        return;
+    }
+
+    if (mst_per_len == 1) {
+        dissect_mdb_ack(tvb, offset, pinfo, tree);
+        return;
+    }
+
+    /*
+     * Our packet has one address byte, an optional data block and one
+     * checksum byte.
+     */
+
+    data_len = mst_per_len - 2;
+
+    /*
+     * The address byte is 5-bit address | 3-bit command.
+     *
+     * The specification uses 8-bit addresses which are the address byte
+     * with the three lowest bits set to 0.
+     *
+     * The commands are defined as the complete address byte (i.e. they
+     * include the address part). This does not make much sense: Cashless #1
+     * and #2 have different addresses but exactly the same 3-bit commands.
+     *
+     * In this dissector, we try to use the same values as the specification.
+     */
+    addr_byte = tvb_get_guint8(tvb, offset);
+    addr = addr_byte & 0xF8;
+    proto_tree_add_uint_bits_format_value(tree, hf_mdb_addr,
+            tvb, 8*offset, 5, addr, ENC_BIG_ENDIAN, "0x%02x", addr);
+    cmd_it = proto_tree_add_uint(tree, hf_mdb_cmd, tvb, offset, 1, addr_byte);
+    mdb_set_addrs(MDB_EVT_DATA_MST_PER, addr, pinfo);
+    offset++;
+
+    /*
+     * We call the peripheral functions even if data_len == 0 so they can fix
+     * up the command with peripheral-specific info.
+     */
+    switch (addr) {
+        case ADDR_CASHLESS1:
+            dissect_mdb_mst_per_cl(tvb, offset, data_len, pinfo, tree,
+                    cmd_it, addr_byte);
+            break;
+        case ADDR_COMMS_GW:
+            dissect_mdb_mst_per_cgw(tvb, offset, data_len, pinfo, tree,
+                    cmd_it, addr_byte);
+            break;
+        default:
+            if (data_len > 0) {
+                proto_tree_add_item(tree, hf_mdb_data,
+                        tvb, offset, data_len, ENC_NA);
+            }
+            break;
+    }
+    offset += data_len;
+
+    /* XXX - verify the checksum */
+    proto_tree_add_item(tree, hf_mdb_chk, tvb, offset, 1, ENC_BIG_ENDIAN);
+}
+
+static void dissect_mdb_per_mst(tvbuff_t *tvb, gint offset, packet_info *pinfo,
+        proto_tree *tree, guint8 addr)
+{
+    gint per_mst_len;
+    guint data_len;
+
+    /*
+     * A packet from peripheral to master is either a single ACK/NAK byte or
+     * a non-empty data block followed by one checksum byte.
+     */
+
+    per_mst_len = tvb_reported_length_remaining(tvb, offset);
+    if (per_mst_len <= 0) {
+        expert_add_info(pinfo, tree, &ei_mdb_short_packet);
+        return;
+    }
+
+    if (per_mst_len == 1) {
+        dissect_mdb_ack(tvb, offset, pinfo, tree);
+        return;
+    }
+
+    data_len = per_mst_len - 1;
+    switch (addr) {
+        case ADDR_CASHLESS1:
+            dissect_mdb_per_mst_cl(tvb, offset, data_len, pinfo, tree);
+            break;
+        case ADDR_COMMS_GW:
+            dissect_mdb_per_mst_cgw(tvb, offset, data_len, pinfo, tree);
+            break;
+        default:
+            proto_tree_add_item(tree, hf_mdb_data, tvb, offset, data_len, ENC_NA);
+            break;
+    }
+    offset += data_len;
+
+    /* XXX - verify the checksum */
+    proto_tree_add_item(tree, hf_mdb_chk, tvb, offset, 1, ENC_BIG_ENDIAN);
+}
+
+static int dissect_mdb(tvbuff_t *tvb,
+        packet_info *pinfo, proto_tree *tree, void *data _U_)
+{
+    gint offset = 0, offset_ver, offset_evt;
+    guint8 version, event, addr;
+    proto_tree *mdb_tree, *hdr_tree;
+    proto_item *tree_ti, *hdr_ti;
+
+    /* We need at least the shortest possible pseudo header. */
+    if (tvb_captured_length(tvb) < 3)
+        return 0;
+
+    offset_ver = offset;
+    version = tvb_get_guint8(tvb, offset++);
+    if (version != 0)
+        return 0;
+
+    offset_evt = offset;
+    event = tvb_get_guint8(tvb, offset++);
+    if (!try_val_to_str(event, mdb_event))
+        return 0;
+
+    col_set_str(pinfo->cinfo, COL_PROTOCOL, "MDB");
+    col_clear(pinfo->cinfo, COL_INFO);
+
+    tree_ti = proto_tree_add_protocol_format(tree, proto_mdb,
+            tvb, 0, tvb_reported_length(tvb), "MDB");
+    mdb_tree = proto_item_add_subtree(tree_ti, ett_mdb);
+
+    hdr_tree = proto_tree_add_subtree(mdb_tree, tvb, 0, -1, ett_mdb_hdr,
+            &hdr_ti, "Pseudo header");
+
+    proto_tree_add_item(hdr_tree, hf_mdb_hdr_ver,
+            tvb, offset_ver, 1, ENC_BIG_ENDIAN);
+    proto_tree_add_item(hdr_tree, hf_mdb_event,
+            tvb, offset_evt, 1, ENC_BIG_ENDIAN);
+
+    /* Packets from peripheral to master always have an address byte in their
+       pseudo header. */
+    if (event == MDB_EVT_DATA_PER_MST) {
+        /* See the comment in dissect_mdb_mst_per about MDB addresses. */
+        addr = tvb_get_guint8(tvb, offset) & 0xF8;
+        proto_tree_add_uint_bits_format_value(hdr_tree, hf_mdb_addr,
+                tvb, 8*offset, 5, addr, ENC_BIG_ENDIAN, "0x%02x", addr);
+        offset++;
+        mdb_set_addrs(event, addr, pinfo);
+    }
+
+    /* We're now at the end of the pseudo header. */
+    proto_item_set_len(hdr_ti, offset);
+
+    if (event == MDB_EVT_BUS_RESET)
+        return offset;
+
+    if (event == MDB_EVT_DATA_MST_PER)
+        dissect_mdb_mst_per(tvb, offset, pinfo, mdb_tree);
+    else if (event == MDB_EVT_DATA_PER_MST)
+        dissect_mdb_per_mst(tvb, offset, pinfo, mdb_tree, addr);
+
+    return tvb_reported_length(tvb);
+}
+
+void proto_register_mdb(void)
+{
+    expert_module_t* expert_mdb;
+
+    static gint *ett[] = {
+        &ett_mdb,
+        &ett_mdb_hdr,
+        &ett_mdb_cl,
+        &ett_mdb_cgw
+    };
+
+    static hf_register_info hf[] = {
+        { &hf_mdb_hdr_ver,
+            { "Version", "mdb.hdr_ver",
+                FT_UINT8, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_event,
+            { "Event", "mdb.event",
+                FT_UINT8, BASE_HEX, VALS(mdb_event), 0, NULL, HFILL }
+        },
+        { &hf_mdb_addr,
+            { "Address", "mdb.addr",
+                FT_UINT8, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cmd,
+            { "Command", "mdb.cmd",
+                FT_UINT8, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_setup_sub,
+            { "Sub-command", "mdb.cashless.setup_sub_cmd",
+                FT_UINT8, BASE_HEX, VALS(mdb_cl_setup_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_feat_lvl,
+            { "Feature level", "mdb.cashless.feature_level",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_cols,
+            { "Columns on display", "mdb.cashless.columns",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_rows,
+            { "Rows on display", "mdb.cashless.rows",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_disp_info,
+            { "Display information", "mdb.cashless.disp_info",
+                FT_UINT8, BASE_HEX, NULL, 0x07, NULL, HFILL }
+        },
+        { &hf_mdb_cl_max_price,
+            { "Maximum price", "mdb.cashless.max_price",
+                FT_UINT32, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_min_price,
+            { "Minimum price", "mdb.cashless.min_price",
+                FT_UINT32, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_vend_sub,
+            { "Sub-command", "mdb.cashless.vend_sub_cmd",
+                FT_UINT8, BASE_HEX, VALS(mdb_cl_vend_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_item_price,
+            { "Item Price", "mdb.cashless.item_price",
+                FT_UINT32, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_item_num,
+            { "Item Number", "mdb.cashless.item_number",
+                FT_UINT32, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_reader_sub,
+            { "Sub-command", "mdb.cashless.reader_sub_cmd",
+                FT_UINT8, BASE_HEX, VALS(mdb_cl_reader_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_resp,
+            { "Response", "mdb.cashless.resp",
+                FT_UINT8, BASE_HEX, VALS(mdb_cl_resp), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_scale,
+            { "Scale factor", "mdb.cashless.scale_factor",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_dec_pl,
+            { "Decimal places", "mdb.cashless.decimal_places",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_max_rsp_time,
+            { "Application maximum response time", "mdb.cashless.max_rsp_time",
+                FT_RELATIVE_TIME, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_vend_amt,
+            { "Vend Amount", "mdb.cashless.vend_amount",
+                FT_UINT32, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_expns_sub,
+            { "Sub-command", "mdb.cashless.expansion_sub_cmd",
+                FT_UINT8, BASE_HEX, VALS(mdb_cl_expns_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_manuf_code,
+            { "Manufacturer Code", "mdb.cashless.manuf_code",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_ser_num,
+            { "Serial Number", "mdb.cashless.serial_number",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_mod_num,
+            { "Model Number", "mdb.cashless.model_number",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cl_opt_feat,
+            { "Optional Feature Bits", "mdb.cashless.opt_feature_bits",
+                FT_UINT32, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_feat_lvl,
+            { "Feature level", "mdb.comms_gw.feature_level",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_scale,
+            { "Scale factor", "mdb.comms_gw.scale_factor",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_dec_pl,
+            { "Decimal places", "mdb.comms_gw.decimal_places",
+                FT_UINT8, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_resp,
+            { "Response", "mdb.comms_gw.resp",
+                FT_UINT8, BASE_HEX, VALS(mdb_cgw_resp), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_max_rsp_time,
+            { "Application maximum response time", "mdb.comms_gw.max_rsp_time",
+                FT_RELATIVE_TIME, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_report_sub,
+            { "Sub-command", "mdb.comms_gw.report_sub_cmd", FT_UINT8,
+                BASE_HEX, VALS(mdb_cgw_report_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_dts_evt_code,
+            { "DTS Event Code", "mdb.comms_gw.dts_event_code",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_duration,
+            { "Duration", "mdb.comms_gw.duration",
+                FT_UINT32, BASE_DEC, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_activity,
+            { "Activity", "mdb.comms_gw.activity",
+                FT_BOOLEAN, 8, TFS(&tfs_active_inactive), 0x1, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_expns_sub,
+            { "Sub-command", "mdb.comms_gw.expansion_sub_cmd", FT_UINT8,
+                BASE_HEX, VALS(mdb_cgw_expns_sub_cmd), 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_opt_feat,
+            { "Optional Feature Bits", "mdb.comms_gw.opt_feature_bits",
+                FT_UINT32, BASE_HEX, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_manuf_code,
+            { "Manufacturer Code", "mdb.comms_gw.manuf_code",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_ser_num,
+            { "Serial Number", "mdb.comms_gw.serial_number",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_cgw_mod_num,
+            { "Model Number", "mdb.comms_gw.model_number",
+                FT_STRING, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_ack,
+            { "Ack byte", "mdb.ack",
+                FT_UINT8, BASE_HEX, VALS(mdb_ack), 0, NULL, HFILL }
+        },
+        { &hf_mdb_data,
+            { "Data", "mdb.data",
+                FT_BYTES, BASE_NONE, NULL, 0, NULL, HFILL }
+        },
+        { &hf_mdb_chk,
+            { "Checksum", "mdb.chk",
+                FT_UINT8, BASE_HEX, NULL, 0, NULL, HFILL }
+        }
+    };
+
+    static ei_register_info ei[] = {
+        { &ei_mdb_short_packet,
+            { "mdb.short_packet", PI_PROTOCOL, PI_ERROR,
+                "MDB packet without payload", EXPFILL }}
+    };
+
+    proto_mdb = proto_register_protocol("Multi-Drop Bus", "MDB", "mdb");
+    proto_register_subtree_array(ett, array_length(ett));
+    proto_register_field_array(proto_mdb, hf, array_length(hf));
+    expert_mdb = expert_register_protocol(proto_mdb);
+    expert_register_field_array(expert_mdb, ei, array_length(ei));
+    mdb_handle = register_dissector("mdb", dissect_mdb, proto_mdb);
+}
+
+void proto_reg_handoff_mdb(void)
+{
+    dissector_add_uint("wtap_encap", WTAP_ENCAP_MDB, mdb_handle);
+}
+
+/*
+ * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
+ *
+ * Local variables:
+ * c-basic-offset: 4
+ * tab-width: 8
+ * indent-tabs-mode: nil
+ * End:
+ *
+ * vi: set shiftwidth=4 tabstop=8 expandtab:
+ * :indentSize=4:tabSize=8:noTabs=true:
+ */