Quick question about reserve symbols

mononaut · 2011-05-03 14:22

I'm pretty new to the spin language (and micro programming in general), so please forgive me if this is a really simple problem.

The RES assembly command allows an optional number of longs to be reserved, but I can't seem to figure out how to refer to any besides the first. I'm working on a project that would benefit from having four longs under one symbol, but once I declare "red res 4," from what I understand, "red" will only refer to the first long in the reserve memory at that address. How can I quickly get the address for the next few longs after the first?

Mike G · 2011-05-03 14:39

You'll probably want self modifying code. This snippet was provided by Mike Green.

DAT
''Snippet - Self modifying code
                        movd   :moveIt,#rxBuffer     ' initialize destination address
                        movs   :moveIt,#otherBuf     ' initialize source address
                        mov     count,#5            ' number of longs to copy.  Also allows for pipeline delay
:moveIt                 mov     0-0,0-0              ' "0-0" is just a placeholder
                        add     :moveIt,bothIncr     ' increment both source and destination
                        djnz    count,#:moveIt       ' count down, loop if not yet zero



bothIncr                long    1<<9 + 1               ' ones line up with source and destination

count                   res     1
rxBuffer                res     5
otherBuf                res     5

mononaut · 2011-05-03 14:53

This is very helpful, thank you! Like I said, I'm still new to micro programming, and I still haven't even trained my brain to think about registers as commands... before you posted that snippet, I'd have taken a long time to figure out what movd and movs are actually for.

Also, the very concept of self-modifying code is very new to me.

kuroneko · 2011-05-03 17:20

mononaut wrote: »

... but once I declare "red res 4," from what I understand, "red" will only refer to the first long in the reserve memory at that address. How can I quickly get the address for the next few longs after the first?

This entirely depends on how you're going to access them. If it's in a loop (array access) then self-modifying code as suggested by Mike (and provided by Mike) is the way to go. If you need one-off access then the following will do:

mov red+0, cnt        ' equivalent to mov red, cnt
    mov red+2, value
    mov red+1, red+3

Quick question about reserve symbols

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