CODEWITHSUNDEEP
assemblyarmraspberry-pitrustzone
AvK
AvK

Reputation: 75

Trust Zone on Raspberry Pi unexpected behaviour?

I am working on the trust zone extension on raspberry pi B+ which has the ARM1176JZF-S processor. According to given documentation on arm11, there will be 3 exception vector tables each for Secure world, Non-secure(NS) world and monitor mode resp. And c12 register will hold the base address of both secure and NS world exception vector table base addresses.

I added both these addresses to the c12 register in their corresponding worlds(Secure / NS). I tried SWI (svc) in both worlds. I found that it is working fine in secure world but in the NS world the control goes to the NS reset handler for a SWI instead of SWI handler. I used the following commands :

For secure world :
    LDR r0, =_start //_start - base address of secure vector table
    MCR p15, 0, r0, c12, c0, 0
For Non-secure World :
    LDR r0, =_ns_start //ns_start - base address of non-secure vector table
    MCR p15, 0, r0, c12, c0, 0

Here is my code : https://github.com/avk7vk/arm_bare_metal/tree/master/trustzone-smc

Please let me know the issue here .

Upvotes: 2

Views: 899

Answers (1)

unixsmurf
unixsmurf

Reputation: 6234

The Vector Base Address Register (VBAR) has the bottom five bits defined as "res0", meaning they will be ignored and treated as zero. As a result, your vector table must be 32-byte aligned. Achieved with:

    .align 5
_ns_start:
    ldr pc, ns_Reset
    ...

Upvotes: 1

Related Questions