PASM JMP instruction DEST field

localroger

Hi all,

I am working on a variation of the LMM.· As in the LMM, I'll be implementing synthetic functions with PASM JMPs to PASM routines in the LMM interpreter cog.· Now, in the Prop manual the JMP instruction SRC field holds the PASM jump target and the DEST field is listed as

---

, which I read as "don't care."· (In the CALL *cough* JMPRET instruction, DEST holds the address of the place where the return jump gets written.)

What I would like to do is use the DEST field as an arbitrary 9-bit argument for some of my PASM synthetic functions.· Can anybody verify that the Prop really doesn't care what JMP finds in the DEST field?· I'd hate to do a lot of work on this only to find that the microcode doesn't really ignore those bits.

I could probably verify this by writing some test code but I figure some of the folks here will simply know the answer straight up.

Mike Green

Yes, the JMP DEST field is available for a 9-bit argument. Look at the instruction. A JMP is just a JMPRET with no result (return address) written.

localroger

Thanks Mike, that's pretty much what I thought... just needed a little confirmation.

Phil Pilgrim (PhiPi)

There's some discussion of the jmpret dst,src nr technique here: http://forums.parallax.com/showthread.php?p=701330

-Phil

localroger

Hi Phil, I was aware of that but it's not what I'm trying to do; I'm pursuing something that is actually less efficient than even Bill's original scheme but buys something even the LMM doesn't get you for the compromise. (And yes, this is Being Cryptic At Parallax day.)