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https://github.com/hsoft/collapseos.git
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178 lines
3.4 KiB
NASM
178 lines
3.4 KiB
NASM
; shell
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;
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; Runs a shell over an asynchronous communication interface adapter (ACIA).
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; Incomplete. For now, this outputs a welcome prompt and then waits for input.
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; Whenever input is CR or LF, we echo back what we've received and empty the
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; input buffer. This also happen when the buffer is full.
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#include "platform.inc"
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; *** CONSTS ***
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CR .equ 0x0d
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LF .equ 0x0a
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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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BUFSIZE .equ 0x20
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; *** VARIABLES ***
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; Our input buffer starts there
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INPTBUF .equ 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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BUFIDX .equ INPTBUF+BUFSIZE
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; *** CODE ***
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jr init
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.fill 0x38-$
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jr handleInterrupt
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init:
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di
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; setup stack
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ld hl, RAMEND
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ld sp, hl
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; initialize variables
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xor a
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ld (BUFIDX), a ; starts at 0
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; RC2014's serial I/O is based on interrupt mode 1. We'd prefer im 2,
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; but for now, let's go with the simpler im 1.
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im 1
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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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; print prompt
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ld hl, d_welcome
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call printstr
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call printcrlf
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; alright, ready to receive
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ei
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mainloop:
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call chkbuf
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jr mainloop
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; read char in the ACIA and put it in the read buffer
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handleInterrupt:
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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 getbufptr ; 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 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 (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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; spits character in A in port SER_OUT
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printc:
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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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; print null-terminated string pointed to by HL
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printstr:
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ld a, (hl) ; load character to send
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or a ; is it zero?
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ret z ; if yes, we're finished
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call printc
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inc hl
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jr printstr
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; no ret because our only way out is ret z above
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printcrlf:
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ld a, CR
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call printc
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ld a, LF
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call printc
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ret
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; check if the input buffer is full or ends in CR or LF. If it does, prints it
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; back and empty it.
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chkbuf:
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call getbufptr
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cp 0
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ret z ; BUFIDX is zero? nothing to check.
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cp BUFSIZE
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jr z, .do ; if BUFIDX == BUFSIZE? do!
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; our previous char is in BUFIDX - 1. Fetch this
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dec hl
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ld a, (hl) ; now, that's our char we have in A
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inc hl ; put HL back where it was
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cp CR
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jr z, .do ; char is CR? do!
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cp LF
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jr z, .do ; char is LF? do!
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; nothing matched? don't do anything
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ret
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.do:
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; terminate our string with 0
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xor a
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ld (hl), a
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; reset buffer index
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ld (BUFIDX), a
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; alright, let's go!
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ld hl, INPTBUF
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call printstr
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call printcrlf
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ret
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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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getbufptr:
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push bc
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ld a, (BUFIDX)
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ld hl, INPTBUF
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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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; *** DATA ***
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d_welcome: .byte "Welcome to Collapse OS", 0
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