From 8c283727a9026cef141cd8b49a9365b0dbe5ca14 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20Veres-Szentkir=C3=A1lyi?= <vsza@vsza.hu>
Date: Wed, 19 Jun 2013 16:45:47 +0200
Subject: [PATCH] added FSKID

---
 run.py  |  4 ++++
 sstv.py | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/run.py b/run.py
index e844d76..17b0c2e 100644
--- a/run.py
+++ b/run.py
@@ -27,6 +27,8 @@ def main():
                         help='bits per sample (default: 16)')
     parser.add_argument('--vox', dest='vox', action='store_true',
                         help='add VOX tones at the beginning')
+    parser.add_argument('--fskid', dest='fskid',
+                        help='add FSKID at the end')
     args = parser.parse_args()
     image = Image.open(args.img_file)
     mode = module_map[args.mode]
@@ -36,6 +38,8 @@ def main():
         raise SystemExit(1)
     s = mode(image, args.rate, args.bits)
     s.vox_enabled = args.vox
+    if args.fskid:
+        s.add_fskid_text(args.fskid)
     s.write_wav(args.wav_file)
 
 
diff --git a/sstv.py b/sstv.py
index b855d68..c17e733 100644
--- a/sstv.py
+++ b/sstv.py
@@ -4,6 +4,7 @@ from __future__ import division, with_statement
 from math import sin, pi, floor
 from random import random
 from contextlib import closing
+from itertools import imap
 import struct
 import wave
 
@@ -14,10 +15,13 @@ FREQ_BLACK = 1500
 FREQ_VIS_START = 1900
 FREQ_WHITE = 2300
 FREQ_RANGE = FREQ_WHITE - FREQ_BLACK
+FREQ_FSKID_BIT1 = 1900
+FREQ_FSKID_BIT0 = 2100
 
 MSEC_VIS_START = 300
 MSEC_VIS_SYNC = 10
 MSEC_VIS_BIT = 30
+MSEC_FSKID_BIT = 22
 
 
 class SSTV(object):
@@ -27,6 +31,7 @@ class SSTV(object):
         self.samples_per_sec = samples_per_sec
         self.bits = bits
         self.vox_enabled = False
+        self.fskid_payload = ''
 
     BITS_TO_STRUCT = {8: 'b', 16: 'h'}
 
@@ -99,10 +104,20 @@ class SSTV(object):
         yield FREQ_SYNC, MSEC_VIS_BIT  # stop bit
         for freq_tuple in self.gen_image_tuples():
             yield freq_tuple
+        for fskid_byte in imap(ord, self.fskid_payload):
+            for _ in xrange(6):
+                bit = fskid_byte & 1
+                fskid_byte >>= 1
+                bit_freq = FREQ_FSKID_BIT1 if bit == 1 else FREQ_FSKID_BIT0
+                yield bit_freq, MSEC_FSKID_BIT
 
     def gen_image_tuples(self):
         return []
 
+    def add_fskid_text(self, text):
+        self.fskid_payload += '\x20\x2a{0}\x01'.format(
+                ''.join(chr(ord(c) - 0x20) for c in text))
+
     def horizontal_sync(self):
         yield FREQ_SYNC, self.SYNC