bt_lo
REGWRITE32(p, bt_lo, 0xff & (r)); \
REGWRITE32((p), bt_lo, TWIN(r)); \
REGWRITE32(p, bt_lo, 0xff & (r)); \
REG(vdac, bt_lo) = ((regno) & 0x00ff); \
REG(vdac, bt_lo) = DUPBYTE0(regno); \
REGWRITE32((p), bt_lo, 0xff & (r)); \
REGWRITE32((p), bt_lo, TWIN(r)); \