AR_MCI_GPM_1
value = MS(REG_READ(ah, AR_MCI_GPM_1), AR_MCI_GPM_WRITE_PTR);
offset = MS(REG_READ(ah, AR_MCI_GPM_1), AR_MCI_GPM_WRITE_PTR);
gpm_ptr = MS(REG_READ(ah, AR_MCI_GPM_1), AR_MCI_GPM_WRITE_PTR);
REG_WRITE(ah, AR_MCI_GPM_1, mci->gpm_len);