commit e1a2886254558c931f79ac5e6362d795a54f1fff
parent d1670a3d26fbb9d1edfc2eb42d84b9da946e928c
Author: Brian Swetland <swetland@frotz.net>
Date: Wed, 18 May 2022 15:47:41 -0700
hw/start.mmu: cleanup
Diffstat:
1 file changed, 21 insertions(+), 26 deletions(-)
diff --git a/hw/src/start.mmu.S b/hw/src/start.mmu.S
@@ -17,20 +17,30 @@
.globl _start
_start:
- // stack is at top of memory
- lw sp, stack_top
+ // zero BSS
+ la t0, __bss_start
+ la t1, __bss_end
+zero_loop:
+ beq t0, t1, zero_done
+ sw zero, 0(t0)
+ add t0, t0, 4
+ j zero_loop
+zero_done:
- // adjust it from vaddr to paddr
- li t0, (0xC0000000 - 0x40000000)
- sub t3, sp, t0
+ // physical memory top
+ // (since it's pc relative and pc is physical right now)
+ la sp, __memory_top
// use the next to last page (before the stack)
// for a bootstrap MMU page directory
li t4, 4096
- sub t1, t3, t4 // t1 = end of pagetable
+ sub t1, sp, t4 // t1 = end of pagetable
sub t0, t1, t4 // t0 = start of pagetable
mv t2, t0 // t2 = pagetable
+ // virtual memory top / boot stack
+ lw sp, start_sp
+
ptbl_zero_loop:
sw zero, 0(t0)
addi t0, t0, 4
@@ -74,26 +84,11 @@ ptbl_map_loop:
nop
nop
- // absolute jump to vaddr entrypoint
- lw t0, _vstart_addr
+ // absolute jump to kernel start
+ lw t0, start_pc
jr t0
-_vstart:
- // zero BSS
- la t0, __bss_start
- la t1, __bss_end
-zero_loop:
- beq t0, t1, zero_done
- sw zero, 0(t0)
- add t0, t0, 4
- j zero_loop
-zero_done:
-
- // jump to kernel entrypoint
- mv a0, sp
- j start
-
-stack_top:
+start_sp:
.word __memory_top
-_vstart_addr:
- .word _vstart
+start_pc:
+ .word start
