Subversion Repositories zipcpu

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;
; Filename:     ivec.S
;
; Project:      Zip CPU -- a small, lightweight, RISC CPU soft core
;
; Purpose:      Just to test whether or not a timer works as desired.  This
;               will set the timer to interrupt every millisecond, and then
;               update a counter on every interrupt.
;
;               On any failure, the processor will execute a BUSY command.
;
; Creator:      Dan Gisselquist, Ph.D.
;               Gisselquist Technology, LLC
;
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;
; Copyright (C) 2015, Gisselquist Technology, LLC
;
; This program is free software (firmware): you can redistribute it and/or
; modify it under the terms of  the GNU General Public License as published
; by the Free Software Foundation, either version 3 of the License, or (at
; your option) any later version.
;
; This program is distributed in the hope that it will be useful, but WITHOUT
; ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
; FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
; for more details.
;
; License:      GPL, v3, as defined and found on www.gnu.org,
;               http://www.gnu.org/licenses/gpl.html
;
;
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;
; Registers:
;       sR0     Peripheral address
;       sR2     Interrupt controller command
;       sR3     Timer peripheral command
;       sR4     User program entry address (Could also be (re)entry address,
;                       but isn't in this implementation)
;       sR5     Whether or not we've gotten the first interrupt
;       sR6     Number of times we've been interrupted
;       sR7     Number of times R6 has overflowed
reset:
        CLR     R0              ; Load the address of the interrupt controller
        LDIHI   $c000h,R0       ; into R0
        LDI     $-1,R2          ; Acknowledge and disable all interrupts
        LDIHI   $7fffh,R2       ;
        STO     R2,(R0)         ;
        ; Set the timer for a programmaable interrupt, every 100k clocks,
        ; or roughly 1,000 times a second on a 100 MHz clock.
        LDIHI   $0xc001h,R3     ; R3 = 100k, save that the top two bits are
        LDILO   $0x86a0h,R3     ; also set (start timer, and auto reload)
        STO     R3,$6(C0)
        ; Now that timer-C is set, let's enable it's interrupts
        LDIHI   $8004h,R2       ; Leaving the bottom all ones acknowledges and
        STO     R2,(R0)         ; clears any interrupts (again)
        ; Clear our counter variables
        CLR     R5
        CLR     R6
        CLR     R7
        ; Program our wait for interrupt routine
        MOV     $8(PC),R4
        MOV     R4,uPC
        RTU
on_first_interrupt:
        ADD     $1,R5
setup_for_next_interrupt:
        RTU
on_subsequent_interrupt:
        ADD     $1,R6
        ADD.C   $1,R7
        BRA     $-4
haltcpu:        
        BUSY                    ; We've failed if we ever get here

waitforinterrupt:
        WAIT
        BRA     $-2
        MOV     $0,R0
        MOV     $0,R0
        BUSY