Mailbox (for comms between cogs)

Rayman · 2025-09-16 12:13

Got some ancient code here that needs updating...
Was started back in the P123 days...

        'Mailbox for USB keys
        Mailbox3=$3FFF8

CON 'graphics constants
    OffscreenBufferAddress=$40000   '320x240 =$12C00
    DisplayBufferAddress=$50000+$3000 'size is 320x240=$12C00 (was 640x480=$4B0000)

It also has two big screen buffers that are towards the top of memory (want to update these as well, but maybe a different topic). Anyway, appears using a fixed memory address for a mailbox that is basically at the top of available memory (or thereabouts).

Kind of wishing there was some standard approach to this. Could use a smart pin in repository mode, but not really liking that idea...

Was just looking at Chip's PSRAM driver and see that he uses some longs in a DAT section as the mailbox:

DAT

cmd_list        long    0[8*3]                  'command list, one set of 3 longs for each cog


                org                             'PSRAM driver

Suppose this is as good a way as any. Seems like would make more sense to me to be in a VAR section, but guess that's nearly the same thing.

The other option might be to figure out where the actual top of memory is and use that. But, think there can be some debug stuff there and also some interrupt things. Maybe should look up where this interrupt stuff is and see if can use that... Most of my codes don't actually use interrupts....

evanh · 2025-09-16 12:27

DAT is global to the program.
VAR is per object instance, although when placed at top level a VAR is effectively a global too.

Wuerfel_21 · 2025-09-16 12:31

Using high memory like that does/should work.
Considering it says Mailbox for USB keys, I would think the best course of action would be to take a flamethrower to anything related to that and replace it with the latest version of usbnew.

Rayman · 2025-09-16 13:11

Looked up where the debug stuff goes:

The debugging program occupies the top 16 KB of hub RAM, remapped to $FC000..$FFFFF and write-protected. The hub RAM at $7C000..$7FFFF will no longer be available.

Don't understand that "remapped" business, but looks like mailbox should be just below $7C000 to avoid the risk of being clobbered by debug...

Mailbox (for comms between cogs)

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