memory address over 0x2000_7ffc is not accessible in mps2-an505

[Changho Choi]

I currently run qemu with the following options
`qemu-system-aarch64 -machine mps2-an505 -cpu cortex-m33 -m 16`

For some reason, memory address over 0x2000_7ffc is not accessible.
It can be tested in gdb as follow.

(gdb) x/x 0x20007ffc
0x20007ffc: 0x00000000
(gdb) x/x 0x20007ffd
0x20007ffd: Cannot access memory at address 0x20007ffd
(gdb) x/x 0x20008000
0x20008000: Cannot access memory at address 0x20008000

[Peter Maydell (pmaydell)]

This is expected behaviour. The memory at 0x2000_0000 in this board is the "FPGA block RAM", and there is only 32K of it, so it finishes at 0x2000_7fff, and attempts to access beyond that will fail because there is no device or memory at the address immediately after it in the memory map.

[Peter Maydell (pmaydell)]

PS: you don't need to pass "-cpu cortex-m33" as it is the default for the mps2-an505 board, and you don't need to pass a -m argument either, as 16MB is the fixed value for this board.

[Peter Maydell (pmaydell)]

(If you were just interested in having a large area of contiguous RAM, the "PSRAM" is the largest lump on this board: it's 16MB starting at 0x8000_0000.)

[Philippe Mathieu-Daudé (philmd)]

On 9/29/20 8:57 AM, Changho Choi wrote:
> Public bug reported:
>
> I currently run qemu with the following options
> `qemu-system-aarch64 -machine mps2-an505 -cpu cortex-m33 -m 16`
>
> For some reason, memory address over 0x2000_7ffc is not accessible.
> It can be tested in gdb as follow.
>
> (gdb) x/x 0x20007ffc
> 0x20007ffc: 0x00000000
> (gdb) x/x 0x20007ffd
> 0x20007ffd: Cannot access memory at address 0x20007ffd

Works for me:

(gdb) x/xg 0x20007ff8
0x20007ff8: 0x0000000000000000

(gdb) x/xw 0x20007ffc
0x20007ffc: 0x00000000

(gdb) x/xh 0x20007ffe
0x20007ffe: 0x0000

(gdb) x/xb 0x20007fff
0x20007fff: 0x00

I suppose GDB uses 32-bit access size by default,
so requesting 32-bit at 0x20007ffd would access
out of bound memory.

> (gdb) x/x 0x20008000
> 0x20008000: Cannot access memory at address 0x20008000

For TYPE_IOTKIT there is only 1 SRAM bank (see armsse_variants[])
initialized to SRAM_ADDR_WIDTH bits, which is 15 by default:

    DEFINE_PROP_UINT32("SRAM_ADDR_WIDTH", ARMSSE, sram_addr_width, 15),

So this MPC downstream region is a 32KB SRAM. The size looks correct.

>
> ** Affects: qemu
> Importance: Undecided
> Status: New
>

[Changho Choi (zpzigi)]

Thank you for all your kind answers and suggestions.
I also have confirmed that the memory address over 0x2000_8000 is not
accessible in the real board.

Regards,

Changho Choi

2020년 9월 29일 (화) 오후 6:25, Peter Maydell <email address hidden>님이 작성:

> (If you were just interested in having a large area of contiguous RAM,
> the "PSRAM" is the largest lump on this board: it's 16MB starting at
> 0x8000_0000.)
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1897680
>
> Title:
> memory address over 0x2000_7ffc is not accessible in mps2-an505
>
> Status in QEMU:
> New
>
> Bug description:
> I currently run qemu with the following options
> `qemu-system-aarch64 -machine mps2-an505 -cpu cortex-m33 -m 16`
>
> For some reason, memory address over 0x2000_7ffc is not accessible.
> It can be tested in gdb as follow.
>
> (gdb) x/x 0x20007ffc
> 0x20007ffc: 0x00000000
> (gdb) x/x 0x20007ffd
> 0x20007ffd: Cannot access memory at address 0x20007ffd
> (gdb) x/x 0x20008000
> 0x20008000: Cannot access memory at address 0x20008000
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/qemu/+bug/1897680/+subscriptions
>