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/*

        Tests of link register behavior in delay slot of l.jal instruction
        
        Testing this:
        l.jal _place
        l.sw 4(r1) r9
        What happens...... (r9 is link register)
Result:
        Appears to confirm that the r9 becomes the return value immediately
        ( at the write-back stage of the l.jal instruction)

        Then testing this:
        l.jal _place
        l.or r9, r0, r0
Result: 
        Writing to link register (r9) in delay slot works, so should be
        avoided (it was illegal according to spec, anyway)
        
*/
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#include "spr-defs.h"
#include "board.h"

/* =================================================== [ exceptions ] === */
        .section .vectors, "ax"


/* ---[ 0x100: RESET exception ]----------------------------------------- */
        .org 0x100      
        l.movhi r0, 0
        /* Clear status register */
        l.ori   r1, r0, SPR_SR_SM
        l.mtspr r0, r1, SPR_SR
        /* Clear timer  */
        l.mtspr r0, r0, SPR_TTMR
        /* Init the stack */
        .global _stack
        l.movhi r1, hi(_stack)
        l.ori   r1, r1, lo(_stack)
        l.addi  r2, r0, -3
        l.and   r1, r1, r2
        /* Jump to program initialisation code */
        .global _start
        l.movhi r4, hi(_start)
        l.ori   r4, r4, lo(_start)
        l.jr    r4
        l.nop


/* =================================================== [ text ] === */
        .section .text

/* =================================================== [ start ] === */ 

        .global _start
        .global _testjalfunc
_start:
        l.addi  r1, r1, -4
        l.movhi r9, hi(0x01234567)
        l.ori   r9, r9, lo(0x01234567)
        l.or    r3, r1, r1 /* copy stack pointer to r3 so we can report it */
        l.nop   0x2
        l.jal   _testjalfunc
        l.sw    0(r1), r9
        l.nop
        l.nop
        l.movhi r3, hi(0x8000000d)
        l.ori   r3, r3, lo(0x8000000d)
        /* Try writing to r9 during delay slot... */
        l.movhi r4, hi(0x15000000) /* standard l.nop */
        l.ori   r5, r4, 0x1 /* l.nop that will exit simulation */
        l.sw    0(r0),  r4 /* Write l.nop to 0x0 */
        l.sw    4(r0),  r4 /* Write l.nop to 0x4 */
        l.sw    8(r0),  r5 /* Write l.nop 0x1 to 0x9 */
        l.sw    12(r0), r4 /* Write l.nop to 0xc */
        l.nop
        l.jal   _testjalfunc
        l.or    r9, r0, r0 /* Clear r9 */
        l.nop   1


_testjalfunc:
        l.nop
        l.nop
        l.nop
        l.nop
        l.nop
        l.jr    r9
        l.nop