AP_Scripting: Add BQ40Z shutdown example

This example intercepts PREFLIGHT_REBOOT_SHUTDOWN COMMAND_LONG's and if
param1==2, it shuts down the BQ40Z smart battery BMS. Otherwise it
passes through the COMMAND_LONG as a COMMAND_INT (this required updating
the gcs:run_command_int to return the MAV_STATUS rather than a bool).

libraries/AP_Scripting/examples/BQ40Z_bms_shutdown.lua

@@ -0,0 +1,108 @@
+-- TI BQ40Z BMS shutdown script
+
+local mavlink_msgs = require("MAVLink/mavlink_msgs")
+
+local COMMAND_ACK_ID = mavlink_msgs.get_msgid("COMMAND_ACK")
+local COMMAND_LONG_ID = mavlink_msgs.get_msgid("COMMAND_LONG")
+local msg_map = {}
+msg_map[COMMAND_ACK_ID] = "COMMAND_ACK"
+msg_map[COMMAND_LONG_ID] = "COMMAND_LONG"
+
+local PARAM_TABLE_KEY = 51
+local PARAM_TABLE_PREFIX = "BATT_BQ40Z_"
+-- add a parameter and bind it to a variable
+local function bind_add_param(name, idx, default_value)
+    assert(param:add_param(PARAM_TABLE_KEY, idx, name, default_value), string.format('could not add param %s', name))
+    return Parameter(PARAM_TABLE_PREFIX .. name)
+end
+assert(param:add_table(PARAM_TABLE_KEY, PARAM_TABLE_PREFIX, 2), 'could not add param table')
+--[[
+  // @Param: BATT_BQ40Z_BUS
+  // @DisplayName: Bus number for the BQ40Z
+  // @Description: Bus number for the BQ40Z
+  // @Range: 0 3
+  // @User: Standard
+--]]
+local BATT_BQ40Z_BUS = bind_add_param('BUS', 1, 0)
+
+
+local MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN = 246
+local MAV_RESULT_ACCEPTED = 0
+local MAV_RESULT_FAILED = 4
+
+-- Initialize MAVLink rx with number of messages, and buffer depth
+mavlink:init(1, 10)
+-- Register message id to receive
+mavlink:register_rx_msgid(COMMAND_LONG_ID)
+-- Block MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN so we can handle the ACK
+mavlink:block_command(MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN)
+
+-- Init BMS i2c device
+local i2c_addr = BATT_BQ40Z_BUS:get()
+assert(i2c_addr ~= nil, "BATT_BQ40Z_BUS not retrievable")
+local bms = i2c:get_device(math.floor(i2c_addr), 0x0B)
+
+-- Exit emergency shutdown (for BQ40Z60, twice for redundancy)
+bms:transfer(string.pack("BBB", 0x00, 0xA7, 0x23), 0)
+bms:transfer(string.pack("BBB", 0x00, 0xA7, 0x23), 0)
+
+-- Function that is returned to the AP scheduler when we want to shutdown
+local function shutdown_loop()
+    local ret = bms:transfer(string.pack("BBB", 0x00, 0x10, 0x00), 0)
+    if ret == nil then
+        gcs:send_text(0, "BQ40Z shutdown transfer failed")
+    end
+
+    return shutdown_loop, 500
+end
+
+-- Main loop
+local function update()
+    local msg, chan = mavlink:receive_chan()
+    local parsed_msg = nil
+
+    if (msg ~= nil) then
+        parsed_msg = mavlink_msgs.decode(msg, msg_map)
+    end
+
+    if parsed_msg ~= nil and (parsed_msg.msgid == COMMAND_LONG_ID) and (parsed_msg.command == MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN) then
+        -- Prepare ack
+        local ack = {}
+        ack.command = parsed_msg.command
+        ack.result = MAV_RESULT_ACCEPTED
+        ack.progress = 0
+        ack.result_param2 = 0
+        ack.target_system = parsed_msg.sysid
+        ack.target_component = parsed_msg.compid
+
+        -- Don't shutdown if armed
+        if arming:is_armed() and parsed_msg.param1 == 2 then
+            gcs:send_text(1, "Not sutting down BQ40Z as vehicle is armed")
+            ack.result = MAV_RESULT_FAILED
+            mavlink:send_chan(chan, mavlink_msgs.encode("COMMAND_ACK", ack))
+
+        -- Shutdown
+        elseif parsed_msg.param1 == 2 then
+            gcs:send_text(1, "Shutting down BQ40Z!!!")
+            mavlink:send_chan(chan, mavlink_msgs.encode("COMMAND_ACK", ack))
+            return shutdown_loop, 0
+
+        -- Pass through the command if it isn't requesting shutdown
+        else
+            local command_int = {
+                p1 = parsed_msg.param1,
+                p2 = parsed_msg.param2,
+                p3 = parsed_msg.param3,
+                p4 = parsed_msg.param4,
+            }
+            local result = gcs:run_command_int(MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN, command_int)
+            ack.result = result
+            mavlink:send_chan(chan, mavlink_msgs.encode("COMMAND_ACK", ack))
+        end
+    end
+
+    return update, 1000
+end
+
+
+return update, 1000

libraries/AP_Scripting/lua_bindings.cpp

@@ -1205,10 +1205,8 @@ int lua_GCS_command_int(lua_State *L)
 
     auto result = _gcs->lua_command_int_packet(pkt);
 
-    // map MAV_RESULT to a boolean
-    bool ok = result == MAV_RESULT_ACCEPTED;
-
-    lua_pushboolean(L, ok);
+    // Return the resulting MAV_RESULT
+    lua_pushinteger(L, result);
 
     return 1;
 }