stratux/extract_metar.go

191 wiersze
4.8 KiB
Go

package main
import (
"bufio"
"bytes"
"encoding/hex"
"fmt"
"log"
"os"
"strings"
)
const (
UPLINK_BLOCK_DATA_BITS = 576
UPLINK_BLOCK_BITS = (UPLINK_BLOCK_DATA_BITS + 160)
UPLINK_BLOCK_DATA_BYTES = (UPLINK_BLOCK_DATA_BITS / 8)
UPLINK_BLOCK_BYTES = (UPLINK_BLOCK_BITS / 8)
UPLINK_FRAME_BLOCKS = 6
UPLINK_FRAME_DATA_BITS = (UPLINK_FRAME_BLOCKS * UPLINK_BLOCK_DATA_BITS)
UPLINK_FRAME_BITS = (UPLINK_FRAME_BLOCKS * UPLINK_BLOCK_BITS)
UPLINK_FRAME_DATA_BYTES = (UPLINK_FRAME_DATA_BITS / 8)
UPLINK_FRAME_BYTES = (UPLINK_FRAME_BITS / 8)
// assume 6 byte frames: 2 header bytes, 4 byte payload
// (TIS-B heartbeat with one address, or empty FIS-B APDU)
UPLINK_MAX_INFO_FRAMES = (424 / 6)
dlac_alpha = "\x03ABCDEFGHIJKLMNOPQRSTUVWXYZ\x1A\t\x1E\n| !\"#$%&'()*+,-./0123456789:;<=>?"
)
var logger *log.Logger
var buf bytes.Buffer
func dlac_decode(data []byte, data_len uint32) string {
fmt.Printf("dlac on %s\n", hex.Dump(data))
step := 0
tab := false
ret := ""
for i := uint32(0); i < data_len; i++ {
var ch uint32
switch step {
case 0:
ch = uint32(data[i+0]) >> 2
case 1:
ch = ((uint32(data[i-1]) & 0x03) << 4) | (uint32(data[i+0]) >> 4)
case 2:
ch = ((uint32(data[i-1]) & 0x0f) << 2) | (uint32(data[i+0]) >> 6)
i = i - 1
case 3:
ch = uint32(data[i+0]) & 0x3f
}
if tab {
for ch > 0 {
ret += " "
ch--
}
tab = false
} else if ch == 28 { // tab
tab = true
} else {
ret += string(dlac_alpha[ch])
}
step = (step + 1) % 4
}
return ret
}
func decodeInfoFrame(frame []byte, frame_start int, frame_len uint32, frame_type uint32) {
data := frame[frame_start : frame_start+int(frame_len)]
if frame_type != 0 {
return // Not FIS-B.
}
if frame_len < 4 {
return // Too short for FIS-B.
}
t_opt := ((uint32(data[1]) & 0x01) << 1) | (uint32(data[2]) >> 7)
product_id := ((uint32(data[0]) & 0x1f) << 6) | (uint32(data[1]) >> 2)
fmt.Printf("%d %d\n", data[0], data[1])
if product_id != 413 { // FIXME.
return
}
if t_opt != 0 { //FIXME.
fmt.Printf("don't know time format %d\n", t_opt)
panic("time format")
}
fisb_hours := (uint32(data[2]) & 0x7c) >> 2
fisb_minutes := ((uint32(data[2]) & 0x03) << 4) | (uint32(data[3]) >> 4)
fisb_length := frame_len - 4
fisb_data := data[4:]
p := dlac_decode(fisb_data, fisb_length)
fmt.Printf("%v\n", p)
logger.Printf("pos=%d,len=%d,t_opt=%d,product_id=%d, time=%d:%d\n", frame_start, frame_len, t_opt, product_id, fisb_hours, fisb_minutes)
}
func decodeUplink(frame []byte) {
position_valid := (uint32(frame[5]) & 0x01) != 0
raw_lat := (uint32(frame[0]) << 15) | (uint32(frame[1]) << 7) | (uint32(frame[2]) >> 1)
raw_lon := ((uint32(frame[2]) & 0x01) << 23) | (uint32(frame[3]) << 15) | (uint32(frame[4]) << 7) | (uint32(frame[5]) >> 1)
lat := float64(raw_lat) * 360.0 / 16777216.0
lon := float64(raw_lon) * 360.0 / 16777216.0
if lat > 90 {
lat = lat - 180
}
if lon > 180 {
lon = lon - 360
}
utc_coupled := (uint32(frame[6]) & 0x80) != 0
app_data_valid := (uint32(frame[6]) & 0x20) != 0
slot_id := uint32(frame[6]) & 0x1f
tisb_site_id := uint32(frame[7]) >> 4
logger.Printf("position_valid=%t, %.04f, %.04f, %t, %t, %d, %d\n", position_valid, lat, lon, utc_coupled, app_data_valid, slot_id, tisb_site_id)
if !app_data_valid {
return // Not sure when this even happens?
}
app_data := frame[8:432]
num_info_frames := 0
pos := 0
total_len := len(app_data)
for (num_info_frames < UPLINK_MAX_INFO_FRAMES) && (pos+2 <= total_len) {
data := app_data[pos:]
frame_length := (uint32(data[0]) << 1) | (uint32(data[1]) >> 7)
frame_type := uint32(data[1]) & 0x0f
if pos+int(frame_length) > total_len {
break // Overrun?
}
if frame_length == 0 && frame_type == 0 {
break // No more frames.
}
pos = pos + 2
decodeInfoFrame(app_data, pos, frame_length, frame_type)
pos = pos + int(frame_length)
}
}
func parseInput(buf string) {
buf = strings.Trim(buf, "\r\n") // Remove newlines.
x := strings.Split(buf, ";") // We want to discard everything before the first ';'.
if len(x) == 0 {
return
}
s := x[0]
if len(s) == 0 {
return
}
logger.Println(buf)
if s[0] != '+' {
return // Only want + ("Uplink") messages currently. - (Downlink) or messages that start with other are discarded.
}
s = s[1:]
if len(s)%2 != 0 { // Bad format.
return
}
if len(s)/2 != UPLINK_FRAME_DATA_BYTES {
fmt.Printf("UPLINK_FRAME_DATA_BYTES=%d, len(s)=%d\n", UPLINK_FRAME_DATA_BYTES, len(s))
panic("Error")
}
// Now, begin converting the string into a byte array.
frame := make([]byte, UPLINK_FRAME_DATA_BYTES)
hex.Decode(frame, []byte(s))
logger.Printf("%v\n", frame)
// Decode the frame.
decodeUplink(frame)
}
func main() {
logger = log.New(&buf, "logger: ", log.Lshortfile)
reader := bufio.NewReader(os.Stdin)
for {
buf, _ := reader.ReadString('\n')
parseInput(buf)
}
}