Interprocessor (51-51d) protocol FAQ

The 51d program running on the 7312 and the Winbond '51 chip communicate over /dev/ttyS1 at 115200 bps.

Here is what we know so far about the communications protocol:

Last byte of multi-byte strings is a checksum that appears to be calculated by (0xff - (all bytes before checksum added together) + 0x01)

Obtained from strace at http://downloads.phathack.com/sbingner/strace-51d.log

Suspected Definitions

#define ACK 0xce
#define ASCII_FOLLOWS 0x50
#define CONTINUE 0xbd
#define ACK_CONTINUE 0xac
#define QUERY_NUM_DISKS 0x21
#define QUERY_NUM_TRACKS 0x20
#define QUERY_DISK_NAME 0x57
#define QUERY_TRACK_NAME 0x56
#define PLAY_TRACK 0x30
#define PING 0x66
#define PONG 0x70

Protocol Examples

ASCII Text is sent 12 Bytes at a time, in multiple 'packets'

7312	8052	Possible Meaning
Initialization
0xf9		??
	0x53	??
0x10		??
	0x21	??
HU Query total disc
	0x21,0xdf	Query total disc
0xce		ACK
0x7d		Total Disks follows
	0xac	OK, Continue
0x00		First byte
	0xbd	Continue
0x0f		Second Byte (total 15 disks)
	0xbd	Continue
0x74		End of Stream
	0xce	ACK
HU Query total tracks
	0x20,0x00,0x01,0xdf	Query total tracks in disc 1 (0x00, 0x01)
0xce		ACK
0x7c		Total tracks follows
	0xac	OK, Continue
0x00		First byte of total tracks
	0xbd	Continue
0x01		Second Byte of total tracks (1 track in disk 1)
	0xbd	Continue
0x00		First byte of disknum
	0xbd	Continue
0x01		Second Byte of disknum
	0xbd	Continue
0x82		End of Stream
	0xce	ACK
Direct play track
	0x30 0x00 0x01 0x00 0x02 0x00 0x00 0xcd	Play Disk 2 Track 1 Offset 0
0xce		ACK
HU ? Name of Disk
	0x57,0x00,0x02,0xa7	Name of disk 2? (Answering "PLY2: Alternative")
0xce		ACK
0x50		ACSII Follows
	0xac	OK, Continue
0x00		Type of Text (0x00 = Disk Name)
	0xbd	Continue
0x00		Packet Number
	0xbd	Continue
P		ASCII Text
	0xbd	Continue
Above 2 lines repeats for each of the letters 'LY2: Altern'
0xc9		Checksum?
	0xce	ACK
0x50		ACSII Follows
	0xac	OK, Continue
0x00		Type of Text (0x00 = Disk Name)
	0xbd	Continue
0x01		Packet Number
	0xbd	Continue
a		ASCII Text
	0xbd	Continue
Above 2 lines repeats for each of the letters 'tive'
0x00		NULL
	0xbd	Continue
Above 2 lines repeat 6 more times
0x96		Checksum?
	0xce	ACK
HU ? Name of Track
	0x56,0x00,0x01,0x00,0x02,0xa7	Name of disk 2, track 1? (returning "3 Doors Down - ")
0xce		ACK
0x50		ACSII Follows
	0xac	OK, Continue
0x01		Type of Text (0x01 = Track Name)
	0xbd	Continue
0x00		Packet Number
	0xbd	Continue
3		ASCII Text
	0xbd	Continue
Above 2 lines repeats for each of the letters ' Doors Down'
0x9d		Checksum?
	0xce	ACK
0x50		ACSII Follows
	0xac	OK, Continue
0x01		Type of Text (0x01 = Track Name)
	0xbd	Continue
0x01		Packet Number
	0xbd	Continue
0x20		ASCII Text (space)
	0xbd	Continue
Above 2 lines repeats for each of the letters ' - Duck And '
0x67		Checksum?
	0xce	ACK
0x50		ACSII Follows
	0xac	OK, Continue
0x01		Type of Text (0x01 = Track Name)
	0xbd	Continue
0x02		Packet Number
	0xbd	Continue
R		ASCII Text
	0xbd	Continue
Above 2 lines repeats for each of the letters 'Run (Live)'
0x00		NULL
	0xbd	Continue
0x00		NULL
	0xbd	Continue
0x77		Checksum?
	0xce	ACK
8052 Ping Request
	0x66, 0x9a	8052 PING
0xce		ACK
0x70		51d PONG
	0xac	ACK, Continue
0x90		Checksum
	0xce	ACK

• Heartbeat:

If the Winbond chip does not see a "heartbeat" signal every 10 seconds, it will kill power to the 7312 and reboot it. It's a two-part sequence:

7312 > 0x70
       0xAC   < 51
     > 0x90
       0xCE   < 51

Must repeat within 10 seconds, or the Winbond chip will output 0x66,0x9A 3 times and reboot.