#37822 - DecayCell - Thu Mar 17, 2005 11:11 am
I'm trying to build a multitasking system on the GBA, but I can't find resources on the net about it -- especially about the assembly context switching part.
I've written a test program, but it fails to work and I have absolutely no way to debug it, since GDB drives me through hell on my GNU/Linux box. I'm attaching the relevant assembly code:
Any help would be GREATLY appreciated.
I've written a test program, but it fails to work and I have absolutely no way to debug it, since GDB drives me through hell on my GNU/Linux box. I'm attaching the relevant assembly code:
| Code: |
| .section ".text"
.align .arm .global _preempt @------------------------------------------------------------------------------- _preempt: @------------------------------------------------------------------------------- @ Disable interrupts mov r0, #0x4000000 add r0,r0,#208 mov r1, #0 strb r1, [r0] @ Copy BIOS-backuped registers from stack to memory ldr r0, =_current_regs sub r1, sp, #24 ldr r2, [r1] str r2, [r0] @ r0 add r0, r0, #4 add r1, r1, #4 ldr r2, [r1] str r2, [r0] @ r1 add r0, r0, #4 add r1, r1, #4 ldr r2, [r1] str r2, [r0] @ r2 add r0, r0, #4 add r1, r1, #4 ldr r2, [r1] str r2, [r0] @ r3 add r0, r0, #36 add r1, r1, #4 ldr r2, [r1] str r2, [r0] @ r12 add r0, r0, #8 add r1, r1, #4 ldr r2, [r1] str r2, [r0] @ lr_irq @ Copy all other general-purpose registers to memory sub r0, r0, #40 str r4, [r0] @ r4 add r0, r0, #4 str r5, [r0] @ r5 add r0, r0, #4 str r6, [r0] @ r6 add r0, r0, #4 str r7, [r0] @ r7 add r0, r0, #4 str r8, [r0] @ r8 add r0, r0, #4 str r9, [r0] @ r9 add r0, r0, #4 str r10, [r0] @ r10 add r0, r0, #4 str r11, [r0] @ r11 @ Switch to System Mode and save sp in memory add r0, r0, #8 mov r1, #0x1f mrs r2, cpsr msr cpsr, r1 str sp, [r0] msr cpsr, r2 @ Copy the saved CPSR to memory ldr r0, =_current_cpsr mrs r1, spsr str r1, [r0] @ Branch to kernel interrupt handler routine ldr r0, =handle_intr bx r0 .global __schedule @------------------------------------------------------------------------------- __schedule: @------------------------------------------------------------------------------- @ Copy BIOS-backuped registers to stack ldr r0, =_current_regs sub r1, sp, #24 ldr r2, [r0] str r2, [r1] @ r0 add r0, r0, #4 add r1, r1, #4 ldr r2, [r0] str r2, [r1] @ r1 add r0, r0, #4 add r1, r1, #4 ldr r2, [r0] str r2, [r1] @ r2 add r0, r0, #4 add r1, r1, #4 ldr r2, [r0] str r2, [r1] @ r3 add r0, r0, #36 add r1, r1, #4 ldr r2, [r0] str r2, [r1] @ r12 add r0, r0, #8 add r1, r1, #4 ldr r2, [r0] str r2, [r1] @ lr_irq @ Copy all other general-purpose registers from memory sub r0, r0, #40 ldr r4, [r0] @ r4 add r0, r0, #4 ldr r5, [r0] @ r5 add r0, r0, #4 ldr r6, [r0] @ r6 add r0, r0, #4 ldr r7, [r0] @ r7 add r0, r0, #4 ldr r8, [r0] @ r8 add r0, r0, #4 ldr r9, [r0] @ r9 add r0, r0, #4 ldr r10, [r0] @ r10 add r0, r0, #4 ldr r11, [r0] @ r11 @ Switch to System Mode and load sp from memory add r0, r0, #8 mov r1, #0x1f mrs r2, cpsr msr cpsr, r1 ldr sp, [r0] msr cpsr, r2 @ Copy saved CPSR back from memory ldr r0, =_current_cpsr ldr r1, [r0] msr spsr, r1 @ Enable interrupts mov r0, #0x4000000 add r0,r0,#208 mov r1, #1 strb r1, [r0] @ Return to BIOS routine bx lr .align .pool .end |
Any help would be GREATLY appreciated.