DISC_DSB
ahc_outb(ahc, DISC_DSB, ~(discenable & 0xff));
ahc_outb(ahc, DISC_DSB + 1, ~((discenable >> 8) & 0xff));
discenable = ~((ahc_inb(ahc, DISC_DSB + 1) << 8)
| ahc_inb(ahc, DISC_DSB));
ahc_outb(ahc, DISC_DSB, ~(discenable & 0xff));
ahc_outb(ahc, DISC_DSB + 1, ~((discenable >> 8) & 0xff));