The Behringer DEQ2496 audio device can have commands sent to it via MIDI, however they require a valid CRC code in order for the device to accept them.
I have thus far been unable to work out how the CRC code is calculated. The manual suggests it is CRC8 however I have not been able to configure a CRC8 algorithm to produce matching values.
Here is some sample data, including valid CRC codes:
The DEQ2496 SysEx manual says of the layout of each of the above files:
blockdata: 7/8 coded: blockno_h, blockno_l, crc, data.
crc: crc8 checksum of blockno_h, blockno_l, data
blockno: transferred 256 byte data block number (bits 21..15, 14..8 of flash offset); blocks 0-0x1f: boot loader; blocks 0x20..0x5ef: application; blocks 0x5f0-0x5ff: startup screen; blocks 0x600-0x67f: presets; blocks 0x680-0x69f: temporary buffers; blocks 0x6a0-0x7ff: hw configuration; block no 0xff00 shows text message data[0..52] on screen
data: data block
I have taken care of the 7/8 coding, so now I have a block of 3+256 bytes, consisting of:
- Offset 0: 16-bit big endian integer, block number
- Offset 2: 8-bit integer, CRC (this is the value I am trying to calculate)
- Offset 3+: Actual data
I've tried a couple of CRC algorithms (with and without a lookup table), written code to run through all possible 8-bit polynomials, initial and final XOR values, and yet I can't find any parameters that work for more than one block.
Although the manual suggests the CRC byte itself is not included in the CRC calculation, I also tried leaving it in place and setting it to various values like
0xFF however this didn't yield any results either.
Is there anyone with more CRC knowledge than me who is able to figure out what they mean here by "crc8 checksum"?