RE: Calculating virtual address from physical address

How is a virtual address=20
calculated for a high address like 0x4F600000?

Add this to the MMU initialzation code (initial_mmu):

/* map leds - 1:1 phys=3Dvirt */
	lis	r3,0x4F600000@h
	ori	r3,r3,0x4F600000@l
	mr	r4,r3
	clrrwi	r4,r4,12
	ori	r4,r4,(TLB_WR|TLB_I|TLB_M|TLB_G)

	clrrwi	r3,r3,12
	ori	r3,r3,(TLB_VALID | TLB_PAGESZ(PAGESZ_4K))

	li	r0,0			/* TLB slot 0 */
	tlbwe	r4,r0,TLB_DATA
	tlbwe	r3,r0,TLB_TAG

Then you have a one to one mapping between physical and virtual memory,=20
and you can access the LEDs at the same address after turning one the
MMU.

BTW, we had a similar problem, but the reason was not turning on the
MMU. The MMU is enabled by writing MSR_KERNEL the status register. This
also enables the machine state exception interrupt.=20

Our hardware design produced PLB bus exceptions, which was unnoticed on
standalone applications. But this bus exceptions also trigger machine
state exceptions. So instead of jumping to start_here the processor
branched to 0x200 - unfortunatly the trap table is not set up at this
point in the boot process...

Alex=20