mirror of
https://github.com/hsoft/collapseos.git
synced 2024-10-06 21:20:56 +11:00
66 lines
1.4 KiB
NASM
66 lines
1.4 KiB
NASM
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; shell
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;
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; Runs a shell over an asynchronous communication interface adapter (ACIA).
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; *** STATUS ***
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; Incomplete. This just outputs the welcome prompt then halts
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; *** PLATFORM ***
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; this is specific to a classic RC2014 setup (8K ROM + 32K RAM). This will be
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; reorganized into something better.
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RAMEND .equ 0xa000
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ACIA_CTL .equ 0x80 ; Control and status. RS off.
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ACIA_IO .equ 0x81 ; Transmit. RS on.
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; *** CONSTS ***
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CR .equ 0x0d
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LF .equ 0x0a
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; *** CODE ***
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jr init
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init:
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di ; no need for interrupts yet
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; setup stack
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ld hl, RAMEND
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ld sp, hl
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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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halt
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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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; *** DATA ***
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d_welcome: .byte "Welcome to Collapse OS", CR, LF, 0
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