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- ; 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 echo
- ; immediately.
- ACIA_BUFSIZE .equ 0x20
-
- ; *** VARIABLES ***
- ; Our input buffer starts there
- ACIA_BUF .equ ACIA_RAMSTART
-
- ; index, in the buffer, where our next character will go. 0 when the buffer is
- ; empty, BUFSIZE-1 when it's almost full.
- ACIA_BUFIDX .equ ACIA_BUF+ACIA_BUFSIZE
- ACIA_RAMEND .equ ACIA_BUFIDX+1
-
- aciaInit:
- ; initialize variables
- xor a
- ld (ACIA_BUFIDX), a ; starts at 0
-
- ; 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
-
- ; 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.
-
- call aciaBufPtr ; HL set, A set
- ; is our input buffer full? If yes, we don't read anything. Something
- ; is wrong: we don't process data fast enough.
- cp ACIA_BUFSIZE
- jr z, .end ; if BUFIDX == BUFSIZE, our buffer is full.
-
- ; increase our buf ptr while we still have it in A
- inc a
- ld (ACIA_BUFIDX), a
-
- in a, (ACIA_IO)
- ld (hl), a
-
- .end:
- pop hl
- pop af
- ei
- reti
-
- ; Set current buffer pointer in HL. The buffer pointer is where our *next* char
- ; will be written. A is set to the value of (BUFIDX)
- aciaBufPtr:
- push bc
-
- ld a, (ACIA_BUFIDX)
- ld hl, ACIA_BUF
- xor b
- ld c, a
- add hl, bc ; hl now points to INPTBUF + BUFIDX
-
- pop bc
- 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
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