pcode_mailbox_rw
err = pcode_mailbox_rw(tile, mbox, &data, NULL, timeout, false, false);
err = pcode_mailbox_rw(tile, mbox, &data0, &data1, timeout, false, false);
err = pcode_mailbox_rw(tile, mbox, val, val1, 1, true, false);
*status = pcode_mailbox_rw(tile, mbox, &request, NULL, 1, true,
ret = pcode_mailbox_rw(tile, PCODE_WRITE_MIN_FREQ_TABLE,