Sysex checksums

[cornutt]

I posted a bit in the Tips forum about assigning sysex to faders. It's really neat for doing a lot of things, but... Some synths, like a lot of Rolands and some E-mus, require a checksum in a sysex message. Would it be possible to add a feature to this so that it can calculate the checksum and insert it into the sysex in place of a code (say, "CC") for each message generated? I don't know how many different checksum algorithms are used by the different manufacturers, so I admit this could be a fair amount of work.

[Jerm]

Cornutt,

That is cool and I am glad you are using this feature. It is rather simple to implement a checksum with the caveat that you mentioned. There are different ways to calculate a checksum and some manufacturers use different algorithms.

I would be willing to implement a feature such as this as long as I had:

1. Adequate documentation decribing the checksum algorithm and
2. sufficient testers to check and make sure it was working on the intended device(s). Note: I do have a bunch of Roland, Korg and Yamaha equipment but I haven't looked at this sysex listing in quite a while. I do not have any E-Mu devices.

[cornutt]

Upon further review, I see in my Proteus/2 manual that it only requires the checksums on patch dump/load sysex messages. Parameter edit messages don't need a sysex.

I have a piece of code laying around somewhere that generates checksums that work with my JD800. I've been told that pretty much all Roland models since about 1990 use the same algorithm. I'll try to find the code and send it to you.

[Jerm]

[cornutt]

Here's my code for computing the Roland checksums. I figured I'd post it here in case anyone else is interested. I've been told that this code works for everything Roland has ever made that requires a checksum (which is pretty much everything they've ever made with MIDI, except for the Juno-106 and the Jupiter retrofit kits). I can testify that this code works with my JD800 and S-750.

Apologies for the funny indenting; the tabs didn't paste properly into the form, and it seems to throw away leading spaces.

-------

unsigned compute_checksum(unsigned char buffer[],
long xstart,
long xend)

{
long first, last; /* start and end of data to be summed */
unsigned sum = 0;
unsigned checksum;
long i;

/*
* Figure out where the data to be summed starts and ends.
* This includes the JD800 address and all of the data except
* the checksum byte itself, but not the EOX, or the
* manufacturer ID, or the first three Roland-specific
* bytes (the unit #, model ID, and command code).
*/
first = xstart+4; /* skip four header bytes */
last = xend-2; /* exclude EOX and the checksum byte */

/* The checksum formula is 128 - (sum of bytes, mod 128). */
for (i = first; i <= last; i++)
sum += buffer[i];
sum &= 0x7f; /* makes it mod 128 */
checksum = 0x80 - sum; /* checksum should be >= 0 && < 0x80 */
/* fix incorrect value of 0x80 if necessary */
if (checksum == 0x80)
checksum = 0;


/* All done */
return(checksum);
}

[Jerm]

it can calculate the checksum and insert it into the sysex in place of a code (say, "CC") for each message generated?

Hmmm.. perhaps "CC" is not the best choice. Perhaps CS or SS would be better.

[cornutt]

Hmmm.. perhaps "CC" is not the best choice. Perhaps CS or SS would be better.

Yeah, that's true, CC might be mistaken for a MIDI channel number.

[Jerm]

I was thinking it is a valid hex byte.

[Jerm]

This is implemented in the 6.0.7.2 pre-release. SS for checksum. However it is completely untested. Can you test this please?

Thanks.

[cornutt]

This is implemented in the 6.0.7.2 pre-release. SS for checksum. However it is completely untested. Can you test this please?

Thanks.

I'll do it as soon as I can. Right now I don't have a MIDI interface that works with OSX. I ordered a MOTU MIDI Express USB, but Sweetwater says they haven't been able to get any from MOTU. Speculation is that it is going to be discontinued and replaced with a Mk II model. I'm going to give it another week, and if MOTU still isn't shipping by then I'll change my order to something else. I am ready to be up and running on X!

[Scoot]

I can recommend a midisport, though it does have a pulsing on light that is a little annoying.

Have no idea what the midi thru button does. On the old serial device you could plug another cable in and run a printer off it. So on midi you would be sequencing and on thru you would be printing.

There is no additional socket to place another cable.


Apart from all that it works.

scoot.

[cornutt]

This is implemented in the 6.0.7.2 pre-release. SS for checksum. However it is completely untested. Can you test this please?

Thanks.

Good news: I just tried it with my JD-800, and it works! Very cool. Thanks. Now it's time for me to go build up a set of instruments that will edit the multi-mode effects settings...