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collapseos/blk/582
Virgil Dupras a9ed8da0b2 acia: simplify driver
The previous approach of maintaining R> and W> pointers was
conceptually simple, but made INT handler code actually quite
complex.

Now, we maintain indexes instead. It's much easier to perform
bounds checks and to compare for equality, something we have to
do quick in the INT handler.
2020-08-14 22:58:05 -04:00

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0x80 CONSTANT ACIA_CTL ( IO port for ACIA's control register )
0x81 CONSTANT ACIA_IO ( IO port for ACIA's data registers )
0x20 CONSTANT ACIA_BUFSZ ( SZ-1 must be a mask )
( Address in memory that can be used variables shared
with ACIA's native words. 4 bytes used. )
CREATE ACIA_MEM SYSVARS 0x70 + ,
( Points to ACIA buf )
: ACIA( ACIA_MEM @ 2+ ;
( Read buf idx Pre-inc )
: ACIAR> ACIA_MEM @ ;
( Write buf idx Post-inc )
: ACIAW> ACIA_MEM @ 1+ ;
( This means that if W> == R>, buffer is full.
If R>+1 == W>, buffer is empty. )