nes-proj/cpu/6502/mtarch-asm.S

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;
; Copyright (c) 2004, Adam Dunkels.
; All rights reserved.
;
; Redistribution and use in source and binary forms, with or without
; modification, are permitted provided that the following conditions
; are met:
; 1. Redistributions of source code must retain the above copyright
; notice, this list of conditions and the following disclaimer.
; 2. Redistributions in binary form must reproduce the above copyright
; notice, this list of conditions and the following disclaimer in the
; documentation and/or other materials provided with the distribution.
; 3. Neither the name of the Institute nor the names of its contributors
; may be used to endorse or promote products derived from this software
; without specific prior written permission.
;
; THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
; ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
; IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
; ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
; FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
; OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
; HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
; OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
; SUCH DAMAGE.
;
; This file is part of the Contiki operating system.
;
; Author: Adam Dunkels <adam@sics.se>
;
; $Id: mtarch-asm.S,v 1.2 2007/08/10 10:45:35 oliverschmidt Exp $
;
;---------------------------------------------------------------------
.import __ZP_START__
.import _mtarch_asm_threadspreg
.import _mtarch_asm_threadzp
.import _mtarch_asm_threadstack
.export _mtarch_asm_start
.export _mtarch_asm_yield
.export _mtarch_asm_exec
;---------------------------------------------------------------------
.bss
kernelspreg: .res 1
zpsave: .res 2
zpspace = 26 ; see <cc65 source>/asminc/zeropage.inc
;---------------------------------------------------------------------
.code
; Switch to thread defined by threadzp, threadstack and threadspreg.
; The kernel CPU stack is swapped onto the threadstack, and the
; CPU stack pointer is saved to the local variable "kernelspreg".
; Also, the zeropage variables are saved.
_mtarch_asm_exec:
sei
; Save kernel CPU stack pointer
tsx
stx kernelspreg
; Save zp locations FE/FF
lda $FE
sta zpsave
lda $FF
sta zpsave+1
; Get zero page buffer addr
lda _mtarch_asm_threadzp
sta $FE
lda _mtarch_asm_threadzp+1
sta $FF
; Swap zero page content with buffer content
ldy #0
: lda <__ZP_START__,y
tax
lda ($FE),y
sta <__ZP_START__,y
txa
sta ($FE),y
iny
cpy #zpspace
bne :-
; Get CPU stack buffer addr
lda _mtarch_asm_threadstack
sta $FE
lda _mtarch_asm_threadstack+1
sta $FF
; Get CPU stack size
ldy kernelspreg ; Determine the smallest of the two stack pointers,
cpy _mtarch_asm_threadspreg ; as we only need to swap the used part of the stack.
bcc :+
ldy _mtarch_asm_threadspreg
; Swap CPU stack content with buffer content
: lda $0100,y
tax
lda ($FE),y
sta $0100,y
txa
sta ($FE),y
iny
bne :-
; Restore zp locations FE/FF
lda zpsave
sta $FE
lda zpsave+1
sta $FF
; Set thread CPU stack pointer
ldx _mtarch_asm_threadspreg
txs
pla
tay
pla
tax
pla
rti
;---------------------------------------------------------------------
; Switch from thread defined by threadzp, threadstack and threadspreg.
; The kernel CPU stack is swapped back from the threadstack, and the
; CPU stack pointer is restored from the local variable "kernelspreg".
; Also, the zeropage variables are restored.
_mtarch_asm_yield:
php
pha
txa
pha
tya
pha
sei
tsx ; The rts adds 1 to the PC
; saved on the stack. We want
lda $0105,x ; the stack to look like is would
clc ; do inside of an interrupt
adc #1 ; (this is what the 'rts' does,
sta $0105,x ; but not the 'rti').
lda $0106,x
adc #0
sta $0106,x
; Save thread CPU stack pointer
tsx
stx _mtarch_asm_threadspreg
; Save zp locations FE/FF
lda $FE
sta zpsave
lda $FF
sta zpsave+1
; Get zero page buffer addr
lda _mtarch_asm_threadzp
sta $FE
lda _mtarch_asm_threadzp+1
sta $FF
; Swap zero page content with buffer content
ldy #0
: lda <__ZP_START__,y
tax
lda ($FE),y
sta <__ZP_START__,y
txa
sta ($FE),y
iny
cpy #zpspace
bne :-
; Get CPU stack buffer addr
lda _mtarch_asm_threadstack
sta $FE
lda _mtarch_asm_threadstack+1
sta $FF
; Get CPU stack size
ldy kernelspreg ; Determine the smallest of the two stack pointers,
cpy _mtarch_asm_threadspreg ; as we only need to swap the used part of the stack.
bcc :+
ldy _mtarch_asm_threadspreg
; Swap CPU stack content with buffer content
: lda $0100,y
tax
lda ($FE),y
sta $0100,y
txa
sta ($FE),y
iny
bne :-
; Restore zp locations FE/FF
lda zpsave
sta $FE
lda zpsave+1
sta $FF
; Set kernel CPU stack pointer
ldx kernelspreg
txs
cli
rts
;---------------------------------------------------------------------
_mtarch_asm_start:
; Save zp locations FE/FF
lda $FE
sta zpsave
lda $FF
sta zpsave+1
; Get zero page buffer addr
lda _mtarch_asm_threadzp
sta $FE
lda _mtarch_asm_threadzp+1
sta $FF
; Copy zero page content to buffer
ldy #$00
: lda <__ZP_START__,y
sta ($FE),y
iny
cpy #zpspace
bne :-
; Restore zp locations FE/FF
lda zpsave
sta $FE
lda zpsave+1
sta $FF
rts
;---------------------------------------------------------------------