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98 lines
2.4 KiB
NASM
98 lines
2.4 KiB
NASM
; acia
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;
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; Manage I/O from an asynchronous communication interface adapter (ACIA).
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; provides "aciaPutC" to put c char on the ACIA as well as an input buffer.
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; You have to call "aciaInt" on interrupt for this module to work well.
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;
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; "aciaInit" also has to be called on boot, but it doesn't call "ei" and "im 1",
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; which is the responsibility of the main asm file, but is needed.
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; *** DEFINES ***
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; ACIA_CTL: IO port for the ACIA's control registers
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; ACIA_IO: IO port for the ACIA's data registers
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; ACIA_RAMSTART: Address at which ACIA-related variables should be stored in
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; RAM.
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; *** CONSTS ***
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; size of the input buffer. If our input goes over this size, we echo
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; immediately.
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ACIA_BUFSIZE .equ 0x20
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; *** VARIABLES ***
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; Our input buffer starts there
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ACIA_BUF .equ ACIA_RAMSTART
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; index, in the buffer, where our next character will go. 0 when the buffer is
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; empty, BUFSIZE-1 when it's almost full.
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ACIA_BUFIDX .equ ACIA_BUF+ACIA_BUFSIZE
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ACIA_RAMEND .equ ACIA_BUFIDX+1
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aciaInit:
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; initialize variables
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xor a
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ld (ACIA_BUFIDX), a ; starts at 0
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; setup ACIA
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; CR7 (1) - Receive Interrupt enabled
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; CR6:5 (00) - RTS low, transmit interrupt disabled.
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; CR4:2 (101) - 8 bits + 1 stop bit
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; CR1:0 (10) - Counter divide: 64
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ld a, 0b10010110
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out (ACIA_CTL), a
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ret
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; read char in the ACIA and put it in the read buffer
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aciaInt:
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push af
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push hl
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; Read our character from ACIA into our BUFIDX
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in a, (ACIA_CTL)
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bit 0, a ; is our ACIA rcv buffer full?
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jr z, .end ; no? a interrupt was triggered for nothing.
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call aciaBufPtr ; HL set, A set
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; is our input buffer full? If yes, we don't read anything. Something
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; is wrong: we don't process data fast enough.
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cp ACIA_BUFSIZE
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jr z, .end ; if BUFIDX == BUFSIZE, our buffer is full.
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; increase our buf ptr while we still have it in A
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inc a
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ld (ACIA_BUFIDX), a
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in a, (ACIA_IO)
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ld (hl), a
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.end:
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pop hl
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pop af
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ei
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reti
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; Set current buffer pointer in HL. The buffer pointer is where our *next* char
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; will be written. A is set to the value of (BUFIDX)
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aciaBufPtr:
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push bc
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ld a, (ACIA_BUFIDX)
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ld hl, ACIA_BUF
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xor b
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ld c, a
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add hl, bc ; hl now points to INPTBUF + BUFIDX
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pop bc
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ret
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; spits character in A in port SER_OUT
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aciaPutC:
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push af
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.stwait:
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in a, (ACIA_CTL) ; get status byte from SER
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bit 1, a ; are we still transmitting?
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jr z, .stwait ; if yes, wait until we aren't
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pop af
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out (ACIA_IO), a ; push current char
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ret
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