collapseos/drv/acia.fs
Virgil Dupras 19d94dfb47 recipes/rc2014: stage1 is too big! saving some space
stripfc requires 2 spaces before "(" to strip a comment. This was
a low hanging fruit for me to get stage1.bin under the 8K line.

That thing is getting tight...
2020-04-17 21:10:48 -04:00

70 lines
1.6 KiB
Forth

( ACIA
Manage I/O from an asynchronous communication interface adapter
(ACIA). provides "EMIT" to put c char on the ACIA as well as
an input buffer. You have to call "~ACIA" on interrupt for
this module to work well.
CONFIGURATION
ACIA_CTL: IO port for the ACIA's control registers
ACIA_IO: IO port for the ACIA's data registers
ACIA_MEM: Address in memory that can be used variables shared
with ACIA's native words. 8 bytes used.
)
0x20 CONSTANT ACIABUFSZ
( Points to ACIA buf )
: ACIA( [ ACIA_MEM 4 + LITN ] ;
( Points to ACIA buf end )
: ACIA) [ ACIA_MEM 6 + LITN ] ;
( Read buf pointer. Pre-inc )
: ACIAR> [ ACIA_MEM LITN ] ;
( Write buf pointer. Post-inc )
: ACIAW> [ ACIA_MEM 2 + LITN ] ;
( This means that if W> == R>, buffer is full.
If R>+1 == W>, buffer is empty. )
: ACIA$
H@ DUP DUP ACIA( ! ACIAR> !
1+ ACIAW> ! ( write index starts one position later )
ACIABUFSZ ALLOT
H@ ACIA) !
( setup ACIA
CR7 (1) - Receive Interrupt enabled
CR6:5 (00) - RTS low, transmit interrupt disabled.
CR4:2 (101) - 8 bits + 1 stop bit
CR1:0 (10) - Counter divide: 64
)
0b10010110 ACIA_CTL PC!
( setup interrupt )
( 4e == INTJUMP )
0xc3 0x4e RAM+ C! ( JP upcode )
['] ~ACIA 0x4f RAM+ !
(im1)
;
: KEY
( inc then fetch )
ACIAR> @ 1+ DUP ACIA) @ = IF
DROP ACIA( @
THEN
( As long as R> == W>-1, it means that buffer is empty )
BEGIN DUP ACIAW> @ = NOT UNTIL
ACIAR> !
ACIAR> @ C@
;
: EMIT
( As long at CTL bit 1 is low, we are transmitting. wait )
BEGIN ACIA_CTL PC@ 0x02 AND UNTIL
( The way is clear, go! )
ACIA_IO PC!
;