--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/py_avrjtag/cmd_proto.py	Sun Feb 22 12:54:45 2009 +0800
@@ -0,0 +1,67 @@
+import struct
+
+CPCMD_PING = 1
+CPCMD_SHIFT_TDI = 2
+CPCMD_SHIFT_TMS = 3
+CPCMD_SHIFT_TDI_TDO = 4
+CPCMD_PONG = 5
+CPCMD_DATA = 6
+CPCMD_ACK = 7
+CPCMD_NAK = 8
+
+def csum_add(csum, c):
+    return (((csum << 3) | (csum >> 5)) ^ c) & 0xff
+
+class cmd(object):
+    OFF_SEQ = 2
+    OFF_DSZ = 3
+    OFF_CODE = 4
+    FRAME_OVERHEAD = 5
+    
+    def __init__(self, seq=0, code=0, data=''):
+        self.seq = seq
+        self.code = code
+        self.data = data
+        pass
+    
+    def to_frame(self):
+        csum = 0
+        csum = csum_add(0, self.code)
+        for c in self.data:
+            csum = csum_add(csum, ord(c))
+            pass
+        csum = csum_add(csum, 0)
+        
+        frame = struct.pack('BBBBB', ord('J'), ord('C'), self.seq,
+                            len(self.data) + 1, self.code)
+        frame = frame + self.data + chr(csum)
+        return frame
+
+    def from_frame(self, frame):
+        if frame[:2] != 'JC':
+            return -1
+        
+        csum = 0
+        for c in frame[self.OFF_CODE:]:
+            csum = csum_add(csum, ord(c))
+            pass
+        if csum:
+            return -1
+        
+        data_sz = ord(frame[self.OFF_DSZ])
+        if data_sz != (len(frame) - self.FRAME_OVERHEAD):
+            return -1
+
+        if not data_sz:
+            return -1
+
+        self.seq = ord(frame[self.OFF_SEQ])
+        self.code = ord(frame[self.OFF_CODE])
+        self.data = frame[self.OFF_CODE + 1:-1]
+        pass
+
+    def __repr__(self):
+        return '<%s {seq: %d, code: %d, data: %s}>' % \
+            (self.__class__.__name__, self.seq, self.code, repr(self.data))
+    pass
+