BIOS_0_SCRATCH
val = aty_ld_le32(BIOS_0_SCRATCH);
aty_st_le32(BIOS_0_SCRATCH, 0x55555555);
if (aty_ld_le32(BIOS_0_SCRATCH) == 0x55555555) {
aty_st_le32(BIOS_0_SCRATCH, 0xAAAAAAAA);
if (aty_ld_le32(BIOS_0_SCRATCH) == 0xAAAAAAAA)
aty_st_le32(BIOS_0_SCRATCH, val); // restore value