mirror of
https://github.com/hsoft/collapseos.git
synced 2024-12-31 06:38:06 +11:00
141 lines
3.4 KiB
NASM
141 lines
3.4 KiB
NASM
; acia
|
|
;
|
|
; Manage I/O from an asynchronous communication interface adapter (ACIA).
|
|
; provides "aciaPutC" to put c char on the ACIA as well as an input buffer.
|
|
; You have to call "aciaInt" on interrupt for this module to work well.
|
|
;
|
|
; "aciaInit" also has to be called on boot, but it doesn't call "ei" and "im 1",
|
|
; which is the responsibility of the main asm file, but is needed.
|
|
|
|
; *** DEFINES ***
|
|
; ACIA_CTL: IO port for the ACIA's control registers
|
|
; ACIA_IO: IO port for the ACIA's data registers
|
|
; ACIA_RAMSTART: Address at which ACIA-related variables should be stored in
|
|
; RAM.
|
|
|
|
; *** CONSTS ***
|
|
; size of the input buffer. If our input goes over this size, we start losing
|
|
; data.
|
|
ACIA_BUFSIZE .equ 0x20
|
|
|
|
; *** VARIABLES ***
|
|
; Our input buffer starts there. This is a circular buffer.
|
|
ACIA_BUF .equ ACIA_RAMSTART
|
|
|
|
; The "read" index of the circular buffer. It points to where the next char
|
|
; should be read. If rd == wr, the buffer is empty. Not touched by the
|
|
; interrupt.
|
|
ACIA_BUFRDIDX .equ ACIA_BUF+ACIA_BUFSIZE
|
|
; The "write" index of the circular buffer. Points to where the next char
|
|
; should be written. Should only be touched by the interrupt. if wr == rd-1,
|
|
; the interrupt will *not* write in the buffer until some space has been freed.
|
|
ACIA_BUFWRIDX .equ ACIA_BUFRDIDX+1
|
|
ACIA_RAMEND .equ ACIA_BUFWRIDX+1
|
|
|
|
aciaInit:
|
|
; initialize variables
|
|
xor a
|
|
ld (ACIA_BUFRDIDX), a ; starts at 0
|
|
ld (ACIA_BUFWRIDX), a
|
|
|
|
; 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
|
|
ld a, 0b10010110
|
|
out (ACIA_CTL), a
|
|
ret
|
|
|
|
; Increase the circular buffer index in A, properly considering overflow.
|
|
; returns value in A.
|
|
aciaIncIndex:
|
|
inc a
|
|
cp ACIA_BUFSIZE
|
|
ret nz ; not equal? nothing to do
|
|
; equal? reset
|
|
xor a
|
|
ret
|
|
|
|
; read char in the ACIA and put it in the read buffer
|
|
aciaInt:
|
|
push af
|
|
push hl
|
|
|
|
; Read our character from ACIA into our BUFIDX
|
|
in a, (ACIA_CTL)
|
|
bit 0, a ; is our ACIA rcv buffer full?
|
|
jr z, .end ; no? a interrupt was triggered for nothing.
|
|
|
|
; Load both read and write indexes so we can compare them. To do so, we
|
|
; perform a "fake" read increase and see if it brings it to the same
|
|
; value as the write index.
|
|
ld a, (ACIA_BUFRDIDX)
|
|
call aciaIncIndex
|
|
ld l, a
|
|
ld a, (ACIA_BUFWRIDX)
|
|
cp l
|
|
jr z, .end ; Equal? buffer is full
|
|
|
|
; Alrighty, buffer not full. let's write.
|
|
ld de, ACIA_BUF
|
|
; A already contains our write index, add it to DE
|
|
call addDE
|
|
; increase our buf ptr while we still have it in A
|
|
call aciaIncIndex
|
|
ld (ACIA_BUFWRIDX), a
|
|
|
|
; And finally, fetch the value and write it.
|
|
in a, (ACIA_IO)
|
|
ld (de), a
|
|
|
|
.end:
|
|
pop hl
|
|
pop af
|
|
ei
|
|
reti
|
|
|
|
|
|
; *** BLOCKDEV ***
|
|
; These function below follow the blockdev API.
|
|
|
|
aciaGetC:
|
|
push de
|
|
|
|
ld a, (ACIA_BUFWRIDX)
|
|
ld e, a
|
|
ld a, (ACIA_BUFRDIDX)
|
|
cp e
|
|
jr z, .nothingToRead ; equal? nothing to read.
|
|
|
|
; Alrighty, buffer not empty. let's read.
|
|
ld de, ACIA_BUF
|
|
; A already contains our read index, add it to DE
|
|
call addDE
|
|
; increase our buf ptr while we still have it in A
|
|
call aciaIncIndex
|
|
ld (ACIA_BUFRDIDX), a
|
|
|
|
; And finally, fetch the value.
|
|
ld a, (de)
|
|
cp a ; ensure Z
|
|
jr .end
|
|
|
|
.nothingToRead:
|
|
call unsetZ
|
|
.end:
|
|
pop de
|
|
ret
|
|
|
|
; spits character in A in port SER_OUT
|
|
aciaPutC:
|
|
push af
|
|
.stwait:
|
|
in a, (ACIA_CTL) ; get status byte from SER
|
|
bit 1, a ; are we still transmitting?
|
|
jr z, .stwait ; if yes, wait until we aren't
|
|
pop af
|
|
out (ACIA_IO), a ; push current char
|
|
ret
|
|
|