[sdiy] My first big project

[Paul Maddox]

David,

> The largest external memory size for AVRs is 64k right?

Nativly addressable, yes..

> if so, then this is a big limitation, hmm lets think about it:
>   128 patterns = 128 * 16 steps * 16 step = 32kb
>   3 songs = 3 * 512 rows * 16 channels = 24kb
>   8 kb for other stuff and furure use and.

I've seen people using 1Mbyte of memory.
You just need to use a 74hc138 and use ChipSelects...
I can think of any 8 bit micros that have more than 64Kbyte of nativly
addressable space.. infact MANY 8bit micros dont have built in support for
external SRAM, you have to write your own 'peek()' and 'poke()' functions.

> I guess you can squeeze in a few songs, if you don't store unused
patterns, rows etc. but as i said I would like to keep it simple,
>ie  fixed size data. Guess I can forget contious controllers, maby I can
squeeze in the controllers in each step, and interpolate,
>inbetween or something.

dont see why you can't.. even with one 74hc138 and using 3 bits on a port
(to control the 74hc138) you can have 512Kbyte of SRAM.
If you dont want to use a 74hc138, you can use say 3 pins as the extra
address pins, manually set them before using the built in support for
external RAM and have as big a chunk of memory as you have spare IO pins..
For example, if you have a 128Kbyte chip, you can use one extra pin, and
have it set for memory address's above 0x0FFFF and cleared for addresses
below 0x10000, giving you 128Kbyte..

Easily done..

Paul