PR_SCBB
mtpr(i, PR_SCBB);
ka6400_txrx(id, "D/I 11 %x\r", mfpr(PR_SCBB)); /* SCB */
ka820_txrx(id, "D/I 11 %x\r", mfpr(PR_SCBB)); /* SCB */
ka88_txrx(id, "D/I 11 %x\r", mfpr(PR_SCBB)); /* SCB */
mtpr(avail_start, PR_SCBB);