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collapseos/drv/acia.fs
Virgil Dupras c56386af02 wip
2020-04-02 23:21:53 -04:00

100 lines
2.1 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
)
0x20 CONSTANT ACIABUFSZ
( Points to ACIA buf )
(sysv) ACIA(
( Points to ACIA buf end )
(sysv) ACIA)
( Read buf pointer. Pre-inc )
(sysv) ACIAR>
( Write buf pointer. Post-inc )
(sysv) ACIAW>
( This means that if W> == R>, buffer is full.
If R>+1 == W>, buffer is empty. )
(entry) ~ACIA
AF PUSHqq,
HL PUSHqq,
DE PUSHqq,
( Read our character from ACIA into our BUFIDX )
ACIA_CTL INAn,
0x01 ANDn, ( is ACIA rcv buf full? )
JRZ, L2 FWR ( end, no, wrong interrupt cause. )
ACIAW> @ LDHL(nn),
( is it == to ACIAR>? )
DE ACIAR> @ LDdd(nn),
( carry cleared from ANDn above )
DE SBCHLss,
JRZ, L3 FWR ( end, buffer full )
( buffer not full, let's write )
ACIA_IO INAn,
(HL) A LDrr,
( advance W> )
HL INCss,
DE ACIAR) @ LDdd(nn),
DE SUBHLss,
JRNZ, L4 FWR ( skip )
( end of buffer reached )
ACIA( @ LDHL(nn),
L4 FSET ( skip )
ACIAW> @ LD(nn)HL,
L3 FSET L2 FSET ( end )
DE POPqq,
HL POPqq,
AF POPqq,
EI,
RETI,
: 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 )
( 51 == INTJUMP )
0xc3 0x51 RAM+ C! ( JP upcode )
['] ~ACIA 0x52 RAM+ !
(im1)
;
: KEY
( As long as R> == W>-1, it means that buffer is empty )
BEGIN ACIAR> @ 1 + ACIAW> @ = NOT UNTIL
ACIAR> @ C@
1 ACIAR> +!
;
: 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 SWAP PC!
;