SCP_ADDR
*(uint32_t *)(SCP_ADDR + 4) = 0xffffffff;
cmd = (SCP_ADDR & 0x0ffffff0) | /* i82586-mode, A24-A31 are omitted */
if ((u16 = *(volatile uint16_t *)(SCP_ADDR + 6)) == 0)
u16 = *(uint16_t *)(SCP_ADDR + 4);