SCRATCH_REG_OFF
reg = litex_read32(reg_addr + SCRATCH_REG_OFF);
litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_TEST_VALUE);
reg = litex_read32(reg_addr + SCRATCH_REG_OFF);
litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_VALUE);