On Thursday, Apr 15, 2004, at 13:52 US/Pacific, Shawn Wilton wrote:

> What would you consider an annoyance in the AVR arch.?
>
>
The general purpose registers aren't.  Many functions must have
particular registers dedicated to their use.

There are peculiar gaps in the instruction set (rather pic-like in that
respect.)  SUBI and SBCI but no ADDI, for instance.  Not a big deal
(SUBI R,-x == ADDI R,X. right?)  But somewhat odd.  Orthogonality is
usually considered a feature of "elegant" instruction sets, and the AVR
doesn't have it...  (If you consider that the AVR was designed for C,
you can probably make guesses why some instructions are there rather
than others, but still...)

Some chips don't have "RAM" (just the "registers"), which reduces them
to nearly to PIC level in terms of being 'annoying.'  Likewise, it
makes a fair number of the neat instructions disappear.

General purpose IO isn't, necessarily.  For instance, the ATtiny28 has
a whole 8 bit port that is input-only (and no other functions, IIRC.)
In general, the PICs are more peripheral-rich (not always usefully so
for every application, of course, but nice from a one-chip-fits-many
perspective.)  (I think this is an area where atmel has been improving,
though...)

BillW

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