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switch to a safe stack in access_exception.

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Assembles, but not tested yet.
This commit is contained in:
Markus Fröschle
2014-01-13 07:19:09 +00:00
parent 3a1c07a2e8
commit a97469a53d
1 changed files with 37 additions and 10 deletions
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47
sys/exceptions.S
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@@ -266,7 +266,7 @@ init_vec_loop:
lea reset_vector(pc),a1 // set reset vector
move.l a1,0x04(a0)
lea access(pc),a1 // set illegal access exception handler
lea access_exception(pc),a1 // set illegal access exception handler
move.l a1,0x08(a0)
.extern _get_bas_drivers
@@ -383,24 +383,44 @@ reset_vector:
beq std_exc_vec // yes->
jmp _rom_entry // no, cold start machine
access:
//
// Triggered when code tries to access a memory area that is not known to the MMU yet.
// This is either a "classic" bus error or the MMU hit a "legal" page not yet mapped.
//
// CAVEAT: if this happens due to the supervisor stack crossing a page boundary, we
// cannot use the supervisor stack in here. Therefore we first switch to a safe stack
// (RAMBAR0, the processor internal SRAM)
access_exception:
move.w #0x2700,sr // disable interrupt
move.l d0,-(sp) // ++ vr
// save current SSP
move.w 4(sp),d0 // get format_status word from stack
move.l sp,__SUP_SP // defined in linker script: top of SRAM0
lea __SUP_SP - 4,sp // now we can savely use the stack
move.l d0,-(sp) // ++ vr
move.l a0,-(sp)
move.l __SUP_SP,a0 // original stack frame
move.w (a0),d0 // get format_status word from stack
andi.l #0x0c03,d0 // mask out fault status bits
cmpi.l #0x0401,d0 // TLB miss on opword of instruction fetch?
beq access_mmu // yes
beq access_exception_mmu // yes
cmpi.l #0x0402,d0 // TLB miss on extension word of instruction fetch?
beq access_mmu // yes
beq access_exception_mmu // yes
cmpi.l #0x0802,d0 // TLB miss on data write?
beq access_mmu // yes
beq access_exception_mmu // yes
cmpi.l #0x0c02,d0 // TLB miss on data read, or read-modify-write?
beq access_mmu // yes
beq access_exception_mmu // yes
// revert stack trickery
move.l (sp)+,a0
move.l (sp)+,d0
move.l __SUP_SP,sp
bra bus_error // everything else is a classic bus error
access_mmu:
access_exception_mmu:
move.l MCF_MMU_MMUSR,d0 // did the last fault hit in TLB?
btst #1,d0 // yes, it did. So we already mapped that page
bne bus_error // and this must be a real bus error
@@ -419,7 +439,12 @@ access_mmu:
movem.l (sp),d0-d1/a0-a2 // restore gcc scratch registers
lea 5*4(sp),sp
move.l (sp)+,d0 // restore register
// revert stack trickery
move.l (sp)+,a0
move.l (sp)+,d0
move.l __SUP_SP,sp
rte
@@ -1008,3 +1033,5 @@ _lowlevel_isr_handler:
movem.l (sp),d0-d1/a0-a1 // restore registers
unlk a6 // cleanup stack
rte
// vim: set syntax=asm68k :