From 2813ad8f5fba721aa45c410ed09f4c616f8fbc02 Mon Sep 17 00:00:00 2001
From: Thomas Watson <twatson52@icloud.com>
Date: Mon, 3 Jun 2024 13:12:18 -0500
Subject: [PATCH] AP_Scripting: add serial device simulation example

---
 libraries/AP_Scripting/examples/gps_synth.lua | 170 ++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100644 libraries/AP_Scripting/examples/gps_synth.lua

diff --git a/libraries/AP_Scripting/examples/gps_synth.lua b/libraries/AP_Scripting/examples/gps_synth.lua
new file mode 100644
index 0000000000000..ef3ce6b00b5a0
--- /dev/null
+++ b/libraries/AP_Scripting/examples/gps_synth.lua
@@ -0,0 +1,170 @@
+-- get GPS data from ardupilot's native bindings then resynthesize into a
+-- virtual NMEA GPS and feed back through the serial device sim bindings.
+-- demonstrates the bindings and provides the opportunity for script-controlled
+-- tampering and other such activities.
+
+-- parameters:
+-- SCR_ENABLE 1
+-- SCR_SDEV_EN 1
+-- SCR_SDEV1_PROTO 5
+-- SERIAL3_PROTOCOL 5
+-- SERIAL4_PROTOCOL -1
+-- GPS2_TYPE 5
+-- GPS_PRIMARY 1
+-- GPS_AUTO_SWITCH 0
+
+local ser_device = serial:find_simulated_device(5, 0)
+if not ser_device then
+  error("SCR_SDEV_EN must be 1 and SCR_SDEVn_PROTO must be 5")
+end
+
+function convert_coord(coord, dir)
+  -- convert ardupilot degrees*1e7 to NMEA degrees + decimal minutes + dir.
+  -- the first character of dir is used if the coordinate is positive,
+  -- the second if negative.
+
+  -- handle sign
+  if coord < 0 then
+    coord = -coord
+    dir = dir:sub(2, 2)
+  else
+    dir = dir:sub(1, 1)
+  end
+
+  local degrees = coord // 10000000 -- integer divide
+  coord = coord - (degrees * 10000000) -- remove that portion
+  local minutes = coord * (60/10000000) -- float divide
+
+  return ("%03d%08.5f,%s"):format(degrees, minutes, dir)
+end
+
+function convert_time(time_week, time_week_ms)
+  -- convert ardupilot GPS time to NMEA UTC date/time strings
+
+  -- GPS week 1095 starts on Dec 31 2000
+  local seconds_per_week = uint32_t(86400*7)
+  timestamp_s = uint32_t(time_week - 1095)*seconds_per_week
+  -- subtract one day to get to Jan 1 2001, then 18 additional seconds to
+  -- account for the GPS to UTC leap second induced offset
+  timestamp_s = timestamp_s - uint32_t(86400 + 18)
+  -- add in time within the week
+  timestamp_s = timestamp_s + (time_week_ms/uint32_t(1000))
+
+  timestamp_s = timestamp_s:toint() -- seconds since Jan 1 2001
+
+  local ts_year = 2001
+  local day_seconds = 86400
+  while true do
+    local year_seconds = day_seconds * ((ts_year % 4 == 0) and 366 or 365)
+    if timestamp_s >= year_seconds then
+      timestamp_s = timestamp_s - year_seconds
+      ts_year = ts_year + 1
+    else
+      break
+    end
+  end
+
+  local month_days = {31, (ts_year % 4 == 0) and 29 or 28,
+    31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
+
+  local ts_month = 1
+  for _, md in ipairs(month_days) do
+    local month_seconds = 86400 * md
+    if timestamp_s >= month_seconds then
+        timestamp_s = timestamp_s - month_seconds
+        ts_month = ts_month + 1
+    else
+      break
+    end
+  end
+
+  local ts_day = 1+(timestamp_s // 86400)
+  timestamp_s = timestamp_s % 86400
+
+  local ts_hour = timestamp_s // 3600
+  timestamp_s = timestamp_s % 3600
+
+  local ts_minute = timestamp_s // 60
+  local ts_second = timestamp_s % 60
+
+  local date = ("%02d%02d%02d"):format(ts_year-2000, ts_month, ts_day)
+  local time = ("%02d%02d%02d.%01d"):format(ts_hour, ts_minute, ts_second,
+    (time_week_ms % 1000):toint()//100)
+
+  return date, time
+end
+
+function get_gps_data(instance)
+  -- get GPS data from ardupilot scripting bindings in native format
+  local data = {
+    hdop = gps:get_hdop(instance),
+    time_week_ms = gps:time_week_ms(instance),
+    time_week = gps:time_week(instance),
+    sats = gps:num_sats(instance),
+    crs = gps:ground_course(instance),
+    spd = gps:ground_speed(instance),
+    loc = gps:location(instance),
+    status = gps:status(instance),
+  }
+  if data.status < gps.GPS_OK_FIX_3D then
+    return nil -- don't bother with invalid data
+  end
+  return data
+end
+
+function arrange_nmea(data)
+  -- convert ardupilot data entries to NMEA-compatible format
+  local ts_date, ts_time = convert_time(data.time_week, data.time_week_ms)
+
+  return {
+    time = ts_time,
+    lat = convert_coord(data.loc:lat(), "NS"),
+    lng = convert_coord(data.loc:lng(), "EW"),
+    spd = data.spd / 0.514, -- m/s to knots
+    crs = data.crs, -- degrees
+    date = ts_date,
+    sats = data.sats,
+    hdop = data.hdop,
+    alt = data.loc:alt()/100,
+  }
+end
+
+function wrap_nmea(msg)
+  -- compute checksum and add header and footer
+  local checksum = 0
+  for i = 1,#msg do
+    checksum = checksum ~ msg:byte(i, i)
+  end
+
+  return ("$%s*%02X\r\n"):format(msg, checksum)
+end
+
+function format_nmea(data)
+  -- format data into complete NMEA sentences
+  local rmc_raw = ("GPRMC,%s,A,%s,%s,%03f,%03f,%s,000.0,E"):format(
+    data.time, data.lat, data.lng, data.spd, data.crs, data.date)
+
+  local gga_raw = ("GPGGA,%s,%s,%s,1,%02d,%05.2f,%06.2f,M,0,M,,"):format(
+    data.time, data.lat, data.lng, data.sats, data.hdop/100, data.alt)
+
+  return wrap_nmea(rmc_raw), wrap_nmea(gga_raw)
+end
+
+function update()
+  -- get data from first instance (we are the second)
+  local ardu_data = get_gps_data(0)
+
+  if ardu_data then
+    local nmea_data = arrange_nmea(ardu_data)
+    local rmc, gga = format_nmea(nmea_data)
+
+    if ser_device:writestring(rmc) ~= #rmc 
+        or ser_device:writestring(gga) ~= #gga then
+      error("overflow, ardupilot is not processing the data, check config!")
+    end
+  end
+
+  return update, 200 -- 5Hz like a real GPS
+end
+
+return update()