parse nmea from socket

pkgs/maps/main.fnl

@@ -1,5 +1,6 @@
 ; (local { : view } (require :fennel))
 (local { : fdopen } (require :posix.stdio))
+(local nmea (require :nmea))
 
 (local {
         : Gtk
@@ -71,7 +72,10 @@ label.readout {
 
 (fn read-gnss [socket]
   (each [l #(socket:read "l")]
-    (print "gnss" l))
+    ; (print "gnss" l)
+    (if (not (= l ""))
+        (print (view (nmea.parse l)))))
+
   true)
 
 (let [sock (gnss-socket:get_socket)

pkgs/maps/nmea.fnl

@@ -3,9 +3,8 @@
 ;; 3-5 are the message type
 ;; fields are comma-delimited
 
-;; we assume that we can parse the message based only on type
-;; (i.e. that the same type should always be parsed the same way no
-;; matter who the talker)
+;; we can parse the message based only on type (i.e. the same type is
+;; always parsed the same way no matter who the talker)
 
 ;; outline: split message into lines, extract values between
 ;; $ and * as talker, type, fields
@@ -50,32 +49,92 @@
   }
  )
 
-(local latlon-signs { :N 1 :S -1 :W -1 :E 1 } )
+(fn try-number [s]
+  (if (= s "")
+      nil
+      (tonumber s)))
 
 (local
  msg-types
  {
+  :GGA
+  (fn [fields]
+    (let [[utc lat latsign lon lonsign
+           fix-quality
+           total-space-vehicles
+           hdop
+           altitude _
+           geoidal-separation _
+           _ _ ] fields
+          latf (if (= lat "")
+                   nil
+                   (* (tonumber lat) 0.01 (case latsign :N 1 :S -1)))
+          lonf (if (= lon "")
+                   nil
+                   (* (tonumber lon) 0.01 (case lonsign :E 1 :W -1)))]
+      { :lat latf
+        :lon lonf
+        : fix-quality
+        :total-space-vehicles (try-number total-space-vehicles)
+        :hdop (try-number hdop)
+        :altitude (try-number altitude)
+        :geoidal-separation (try-number geoidal-separation)
+        }))
+
+  :RMC
+  (fn [[utc valid lat latsign lon lonsign
+        knots bearing-true date
+        magn-var magn-var-sign
+        mode nav-status &as fields]]
+    (let [latf (if (= lat "")
+                   nil
+                   (* (tonumber lat) 0.01 (case latsign :N 1 :S -1)))
+          lonf (if (= lon "")
+                   nil
+                   (* (tonumber lon) 0.01 (case lonsign :E 1 :W -1)))
+          magnetic-variation (if (= magn-var "")
+                                 nil
+                                 (* (tonumber magn-var)
+                                    (case magn-var-sign :E 1 :W -1)))]
+      { : utc
+        : valid
+        :lat latf
+        :lon lonf
+        :speed-knots (try-number knots)
+        :bearing-true (try-number bearing-true)
+        : date
+        : magnetic-variation
+        : mode
+        }))
+
   :GNS
   (fn [fields]
     (let [[utc lat latsign lon lonsign mode total-space-vehicles
-           hdop altitude geoidal-separation _ _ nav-status] fields]
-      { :lat (* (/ (tonumber lat) 100) (. latlon-signs latsign))
-        :lon (* (/ (tonumber lon) 100) (. latlon-signs lonsign))
+           hdop altitude geoidal-separation _ _ nav-status] fields
+          latf (if (= lat "")
+                   nil
+                   (* (tonumber lat) 0.01 (case latsign :N 1 :S -1)))
+          lonf (if (= lon "")
+                   nil
+                   (* (tonumber lon) 0.01 (case lonsign :E 1 :W -1)))]
+      { :lat latf
+        :lon lonf
         : mode
-        :total-space-vehicles (tonumber total-space-vehicles)
-        :hdop (tonumber hdop)
-        :altitude (tonumber altitude)
-        :geoidal-separation (tonumber geoidal-separation)
+        :total-space-vehicles (try-number total-space-vehicles)
+        :hdop (try-number hdop)
+        :altitude (try-number altitude)
+        :geoidal-separation (try-number geoidal-separation)
         : nav-status
         }
       ))
+
   :VTG
   (fn [[bearing-true _ bearing-mag _ knots _ kmh _ mode]]
     {
-     :bearing-true (tonumber bearing-true)
-     :bearing-magnetic (tonumber bearing-mag)
-     :speed-knots (tonumber knots)
-     :speed-kmh (tonumber kmh)
+     :bearing-true (try-number bearing-true)
+     :bearing-magnetic (try-number bearing-mag)
+     :speed-knots (try-number knots)
+     :speed-kmh (try-number kmh)
      : mode
      }
     )
@@ -117,3 +176,5 @@
   :speed-kmh 2.9
   :mode :A
   })
+
+{ :parse parse-line }