reset-vector issue

[zjin8520]

Hi,

when I use these parameters "--xlen 64 --with-mul --with-div --with-rva --with-rvZb --with-boot-mem-init --reset-vector 0x0 --physical-width 32" to generate the VexiiRisc.v, the FetchCachelessPlugin_logic-bus_cmd_valid can't assert to fetch the code, is there something wrong?

thanks a lot

[Dolu1990]

Hi,

So far,nearly all simulation of VexiiRIscv were done using Verilator, which doesn't have x-prop simulation.
You likely have hit a xprop issue. Then if that's a bug, or a false bug i don't know.

Can you sent me your wave ? As a VCD or a FST ?

[zjin8520]

Hi Sir,

I'm very sorry I can't provide the VCD format waveform immediately, but I tried to trace this problem, I found the following code, maybe it's the root cause? Please try to analyse the code snippet, if you still need the VCD file, please let me know and I will try to generate it. Thank you very much!

[zjin8520]

Hi Sir,

And I found another problem? When I try to use "--reset-vector 0x8F00000000000000 --physical-width 64" to generate RTL, I got the following error message. Actuaully, if reset-vectore's bit[63] is 1, the error will occur. Most of my job is verification, so I like to try some corner cases, sorry....

[Jzjerry]

Hi,

And I found another problem? When I try to use "--reset-vector 0x8F00000000000000 --physical-width 64" to generate RTL, I got the following error message. Actually, if reset-vectore's bit[63] is 1, the error will occur. Most of my job is verification, so I like to try some corner cases, sorry....

That should be because Long is used for reset-vector, so bit 63 is the sign bit of a Long, and the value of a Long should be less than +2^63.
As unsigned integers are not included in Scala, the solution might be to use BigInt instead, which is aligned with PcPlugin as well:

VexiiRiscv/src/main/scala/vexiiriscv/Param.scala

Line 66 in 7b50ac8

var resetVector = 0x80000000l

to var resetVector : BigInt = 0x80000000l.

VexiiRiscv/src/main/scala/vexiiriscv/Param.scala

Line 263 in 7b50ac8

opt[Long]("reset-vector") unbounded() action { (v, c) => resetVector = v }

to opt[BigInt]("reset-vector").
That should fix it.

[Dolu1990]

Hi,

So the reason why 0x0 can't be used is that by default the PMA specification used by VexiiRiscv is :

VexiiRiscv/src/main/scala/vexiiriscv/Param.scala

Line 25 in 7b50ac8

def setPma(plugins : Seq[Hostable]) = {

Which mean, address zero is unmapped, and will always fault.

We need to add a way to parametrized the PMA specification via arguments.

--reset-vector 0x8F00000000000000 --physical-width 64

I would say, avoid 64 bits physical memory address space, as anyway, no mmu allows such width, aswell as it create overhead in the CPU.

optBigInt

Yes right :)

[zjin8520]

Hi Sir,

got it, thanks for your help :)