[Qemu-devel] Memory read/write issues (was: Initializing PC from memory on reset?)

["Andreas Färber" <andreas.faerber@web.de>]

Am 24.11.2011 00:59, schrieb Andreas Färber:
> Unlike PowerPC, an architecture that I'm trying to emulate does not
> store branch instructions in the reset vector but a memory address. I'm
> therefore trying to read physical address 0x00000 and store its value
> into my env->pc.
> 
> I've verified by running with -S that xp /xh 0x00000 shows the expected
> value.
> 
> When doing lduw_phys(0x00000) or cpu_read_physical_memory() in the CPU
> reset function though, I just seem to read from uninitialized memory
> (0xbaba). I've taken care to reorder CPU initialization to after the
> BIOS file is loaded in the machine initialization function.

Another weird memory issue is that tcg_gen_qemu_st16() succeeds but the
value stored doesn't show up with xp or x on the monitor but 0x0000.

MOVW 0xf8,#0xfee0 (at 0x02010) is trying to write 0xfee0 to 0xFFFf8.

Similarly, a subsequent tcg_gen_qemu_ld16u() reads 0x0000 from there.

TCG snippet:
https://github.com/afaerber/qemu-rl78/commit/d3880bd53a26d224c56d16a6ea5950019d411cf0

            uint8_t sfrp = ldub_code(s->pc + 1) & ~0x1;
            uint16_t data = lduw_code(s->pc + 2);
            LOG_DISAS("MOVW 0x%" PRIx8 ",#0x%04" PRIx16 "\n", sfrp, data);
            TCGv addr = tcg_const_tl(0xFFF00 | sfrp);
            TCGv_i32 val = tcg_const_i32(data);
            tcg_gen_qemu_st16(val, addr, 0);

/* for testing: */
        tcg_gen_qemu_ld16u(env_sp, addr, 0);

            tcg_temp_free(addr);
            tcg_temp_free(val);

(qemu) info mtree
memory
00000000-fffffffe (prio 0): system
  00000000-0000ffff (prio 0): rl78g13_pb.code_flash
  000fef00-000ffeff (prio 0): rl78g13_pb.ram
    000ffee0-000ffeff (prio 0): rl78g13_pb.gpr
  000fff00-000fffff (prio 0): rl78g13_pb.sfr

https://github.com/afaerber/qemu-rl78/blob/d3880bd53a26d224c56d16a6ea5950019d411cf0/hw/rl78g13_pb.c#L88

    memory_region_init_ram(sfr, NULL, "rl78g13_pb.sfr", 256);
    memory_region_add_subregion(get_system_memory(), 0xFFF00, sfr);

Anything obvious that I'm missing?

Thanks,
Andreas