diff --git a/sys/dev/ata/ata_wdc.c b/sys/dev/ata/ata_wdc.c
index 3baa3576d5c7..ebe0885a2e17 100644
--- a/sys/dev/ata/ata_wdc.c
+++ b/sys/dev/ata/ata_wdc.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: ata_wdc.c,v 1.15 1999/02/21 00:52:04 hubertf Exp $	*/
+/*	$NetBSD: ata_wdc.c,v 1.16 1999/03/07 14:02:53 bouyer Exp $	*/
 
 /*
  * Copyright (c) 1998 Manuel Bouyer.
@@ -114,13 +114,14 @@ int wdcdebug_wd_mask = 0;
 #define WDCDEBUG_PRINT(args, level)
 #endif
 
-#define ATA_DELAY 10000 /* 10s for a drive I/O */
+#define ATA_DELAY_NORMAL 1000 /* 1s for a normal drive I/O */
+#define ATA_DELAY_RECOVERY 10000 /* 10s for setup or recovery drive I/O */
 
 void  wdc_ata_bio_start  __P((struct channel_softc *,struct wdc_xfer *));
 int   wdc_ata_bio_intr   __P((struct channel_softc *, struct wdc_xfer *));
 void  wdc_ata_bio_done   __P((struct channel_softc *, struct wdc_xfer *)); 
 int   wdc_ata_ctrl_intr __P((struct channel_softc *, struct wdc_xfer *));
-int   wdc_ata_err __P((struct channel_softc *, struct ata_bio *));
+int   wdc_ata_err __P((struct ata_drive_datas *, struct ata_bio *));
 #define WDC_ATA_NOERR 0x00 /* Drive doesn't report an error */
 #define WDC_ATA_RECOV 0x01 /* There was a recovered error */
 #define WDC_ATA_ERR   0x02 /* Drive reports an error */
@@ -165,6 +166,7 @@ wdc_ata_bio_start(chp, xfer)
 	u_int16_t cyl;
 	u_int8_t head, sect, cmd = 0;
 	int nblks;
+	int ata_delay;
 	int dma_flags = 0;
 
 	WDCDEBUG_PRINT(("wdc_ata_bio_start %s:%d:%d\n",
@@ -188,13 +190,14 @@ wdc_ata_bio_start(chp, xfer)
 		xfer->c_intr = wdc_ata_ctrl_intr;
 		bus_space_write_1(chp->cmd_iot, chp->cmd_ioh, wd_sdh,
 		    WDSD_IBM | (xfer->drive << 4));
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY) != 0)
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY) != 0)
 			goto timeout;
 		wdccommandshort(chp, xfer->drive, WDCC_RECAL);
 		drvp->state = RECAL_WAIT;
 		if ((ata_bio->flags & ATA_POLL) == 0) {
 			chp->ch_flags |= WDCF_IRQ_WAIT;
-			timeout(wdctimeout, chp, ATA_DELAY / 1000 * hz);
+			timeout(wdctimeout, chp,
+			    ATA_DELAY_RECOVERY / 1000 * hz);
 		} else {
 			/* Wait for at last 400ns for status bit to be valid */
 			delay(1);
@@ -207,6 +210,10 @@ wdc_ata_bio_start(chp, xfer)
 		dma_flags = (ata_bio->flags & ATA_READ) ?  WDC_DMA_READ : 0;
 		dma_flags |= (ata_bio->flags & ATA_POLL) ?  WDC_DMA_POLL : 0;
 	}
+	if (ata_bio->flags & ATA_SINGLE)
+		ata_delay = ATA_DELAY_RECOVERY;
+	else
+		ata_delay = ATA_DELAY_NORMAL;
 again:
 	/*
 	 *
@@ -276,7 +283,7 @@ again:
 			/* Initiate command */
 			bus_space_write_1(chp->cmd_iot, chp->cmd_ioh, wd_sdh,
 			    WDSD_IBM | (xfer->drive << 4));
-			if (wait_for_ready(chp, ATA_DELAY) < 0)
+			if (wait_for_ready(chp, ata_delay) < 0)
 				goto timeout;
 			wdccommand(chp, xfer->drive, cmd, cyl,
 			    head, sect, nblks, 0);
@@ -298,7 +305,7 @@ again:
 		/* Initiate command! */
 		bus_space_write_1(chp->cmd_iot, chp->cmd_ioh, wd_sdh,
 		    WDSD_IBM | (xfer->drive << 4));
-		if (wait_for_ready(chp, ATA_DELAY) < 0)
+		if (wait_for_ready(chp, ata_delay) < 0)
 			goto timeout;
 		wdccommand(chp, xfer->drive, cmd, cyl,
 		    head, sect, nblks, 
@@ -314,17 +321,17 @@ again:
 	}
 	/* If this was a write and not using DMA, push the data. */
 	if ((ata_bio->flags & ATA_READ) == 0) {
-		if (wait_for_drq(chp, ATA_DELAY) != 0) {
+		if (wait_for_drq(chp, ata_delay) != 0) {
 			printf("%s:%d:%d: timeout waiting for DRQ, "
 			    "st=0x%02x, err=0x%02x\n",
 			    chp->wdc->sc_dev.dv_xname, chp->channel,
 			    xfer->drive, chp->ch_status, chp->ch_error);
-			if (wdc_ata_err(chp, ata_bio) != WDC_ATA_ERR)
+			if (wdc_ata_err(drvp, ata_bio) != WDC_ATA_ERR)
 				ata_bio->error = TIMEOUT;
 			wdc_ata_bio_done(chp, xfer);
 			return;
 		}
-		if (wdc_ata_err(chp, ata_bio) == WDC_ATA_ERR) {
+		if (wdc_ata_err(drvp, ata_bio) == WDC_ATA_ERR) {
 			wdc_ata_bio_done(chp, xfer);
 			return;
 		}
@@ -362,7 +369,7 @@ again:
 intr:	/* Wait for IRQ (either real or polled) */
 	if ((ata_bio->flags & ATA_POLL) == 0) {
 		chp->ch_flags |= WDCF_IRQ_WAIT;
-		timeout(wdctimeout, chp, ATA_DELAY / 1000 * hz);
+		timeout(wdctimeout, chp, ata_delay / 1000 * hz);
 	} else {
 		/* Wait for at last 400ns for status bit to be valid */
 		delay(1);
@@ -375,7 +382,7 @@ timeout:
 	printf("%s:%d:%d: not ready, st=0x%02x, err=0x%02x\n",
 	    chp->wdc->sc_dev.dv_xname, chp->channel, xfer->drive,
 	    chp->ch_status, chp->ch_error);
-	if (wdc_ata_err(chp, ata_bio) != WDC_ATA_ERR)
+	if (wdc_ata_err(drvp, ata_bio) != WDC_ATA_ERR)
 		ata_bio->error = TIMEOUT;
 	wdc_ata_bio_done(chp, xfer);
 	return;
@@ -410,7 +417,7 @@ wdc_ata_bio_intr(chp, xfer)
 	}
 
 	/* Ack interrupt done by wait_for_unbusy */
-	if (wait_for_unbusy(chp, ATA_DELAY) < 0) {
+	if (wait_for_unbusy(chp, ATA_DELAY_NORMAL) < 0) {
 		printf("%s:%d:%d: device timeout, c_bcount=%d, c_skip%d\n",
 		    chp->wdc->sc_dev.dv_xname, chp->channel, xfer->drive,
 		    xfer->c_bcount, xfer->c_skip);
@@ -425,7 +432,7 @@ wdc_ata_bio_intr(chp, xfer)
 		return 1;
 	}
 	
-	drv_err = wdc_ata_err(chp, ata_bio);
+	drv_err = wdc_ata_err(drvp, ata_bio);
 
 	/* If we were using DMA, Turn off the DMA channel and check for error */
 	if (xfer->c_flags & C_DMA) {
@@ -437,7 +444,7 @@ wdc_ata_bio_intr(chp, xfer)
 			 * asserted for DMA transfers, so poll for DRDY.
 			 */
 			if (wdcwait(chp, WDCS_DRDY | WDCS_DRQ, WDCS_DRDY,
-			    ATA_DELAY) < 0) {
+			    ATA_DELAY_NORMAL) < 0) {
 				printf("%s:%d:%d: polled transfer timed out "
 				    "(st=0x%x)\n", chp->wdc->sc_dev.dv_xname,
 				    chp->channel, xfer->drive, chp->ch_status);
@@ -593,7 +600,7 @@ again:
 
 	case RECAL_WAIT:
 		errstring = "recal";
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY))
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY))
 			goto timeout;
 		if (chp->ch_status & (WDCS_ERR | WDCS_DWF))
 			goto error;
@@ -613,7 +620,7 @@ again:
 
 	case PIOMODE_WAIT:
 		errstring = "piomode";
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY))
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY))
 			goto timeout;
 		if (chp->ch_status & (WDCS_ERR | WDCS_DWF))
 			goto error;
@@ -633,7 +640,7 @@ again:
 		break;
 	case DMAMODE_WAIT:
 		errstring = "dmamode";
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY))
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY))
 			goto timeout;
 		if (chp->ch_status & (WDCS_ERR | WDCS_DWF))
 			goto error;
@@ -653,7 +660,7 @@ again:
 
 	case GEOMETRY_WAIT:
 		errstring = "geometry";
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY))
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY))
 			goto timeout;
 		if (chp->ch_status & (WDCS_ERR | WDCS_DWF))
 			goto error;
@@ -670,7 +677,7 @@ again:
 
 	case MULTIMODE_WAIT:
 		errstring = "setmulti";
-		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY))
+		if (wdcwait(chp, WDCS_DRDY, WDCS_DRDY, ATA_DELAY_RECOVERY))
 			goto timeout;
 		if (chp->ch_status & (WDCS_ERR | WDCS_DWF))
 			goto error;
@@ -689,7 +696,7 @@ again:
 
 	if ((ata_bio->flags & ATA_POLL) == 0) {
 		chp->ch_flags |= WDCF_IRQ_WAIT;
-		timeout(wdctimeout, chp, ATA_DELAY / 1000 * hz);
+		timeout(wdctimeout, chp, ATA_DELAY_RECOVERY / 1000 * hz);
 	} else {
 		goto again;
 	}
@@ -723,10 +730,11 @@ error:
 }
 
 int
-wdc_ata_err(chp, ata_bio)
-	struct channel_softc *chp;
+wdc_ata_err(drvp, ata_bio)
+	struct ata_drive_datas *drvp;
 	struct ata_bio *ata_bio;
 {
+	struct channel_softc *chp = drvp->chnl_softc;
 	ata_bio->error = 0;
 	if (chp->ch_status & WDCS_BSY) {
 		ata_bio->error = TIMEOUT;
@@ -741,6 +749,14 @@ wdc_ata_err(chp, ata_bio)
 	if (chp->ch_status & WDCS_ERR) {
 		ata_bio->error = ERROR;
 		ata_bio->r_error = chp->ch_error;
+		if (drvp->drive_flags & DRIVE_UDMA &&
+		    (ata_bio->r_error & WDCE_CRC)) {
+			/*
+			 * Record the CRC error, to avoid downgrading to
+			 * multiword DMA
+			 */
+			drvp->drive_flags |= DRIVE_DMAERR;
+		}
 		if (ata_bio->r_error & (WDCE_BBK | WDCE_UNC | WDCE_IDNF |
 		    WDCE_ABRT | WDCE_TK0NF | WDCE_AMNF))
 			return WDC_ATA_ERR;
diff --git a/sys/dev/ata/atavar.h b/sys/dev/ata/atavar.h
index 23aa5a5bf74d..095d7c8af099 100644
--- a/sys/dev/ata/atavar.h
+++ b/sys/dev/ata/atavar.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: atavar.h,v 1.11 1999/01/29 11:36:20 bouyer Exp $	*/
+/*	$NetBSD: atavar.h,v 1.12 1999/03/07 14:02:53 bouyer Exp $	*/
 
 /*
  * Copyright (c) 1998 Manuel Bouyer.
@@ -48,6 +48,7 @@ struct ata_drive_datas {
 #define DRIVE_UDMA  0x10
 #define DRIVE_MODE 0x20 /* the drive reported its mode */
 #define DRIVE_RESET 0x40 /* reset the drive state at next xfer */
+#define DRIVE_DMAERR 0x80 /* Udma transfer had crc error, don't try DMA */
     /*
      * Current setting of drive's PIO, DMA and UDMA modes.
      * Is initialised by the disks drivers at attach time, and may be
diff --git a/sys/dev/ic/wdc.c b/sys/dev/ic/wdc.c
index 3ca8d44a888f..15b8c22e87e0 100644
--- a/sys/dev/ic/wdc.c
+++ b/sys/dev/ic/wdc.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: wdc.c,v 1.60 1999/02/21 02:07:52 abs Exp $ */
+/*	$NetBSD: wdc.c,v 1.61 1999/03/07 14:02:54 bouyer Exp $ */
 
 
 /*
@@ -943,14 +943,22 @@ wdc_downgrade_mode(drvp)
 	    (cf_flags & ATA_CONFIG_UDMA_SET))
 		return 0;
 
-	if (drvp->drive_flags & DRIVE_UDMA) {
+	/*
+	 * If we were using ultra-DMA, don't downgrade to multiword DMA
+	 * if we noticed a CRC error. It has been noticed that CRC errors
+	 * in ultra-DMA lead to silent data corruption in multiword DMA.
+	 * Data corruption is less likely to occur in PIO mode.
+	 */
+
+	if ((drvp->drive_flags & DRIVE_UDMA) &&
+	    (drvp->drive_flags & DRIVE_DMAERR) == 0) {
 		drvp->drive_flags &= ~DRIVE_UDMA;
 		drvp->drive_flags |= DRIVE_DMA;
 		drvp->DMA_mode = drvp->DMA_cap;
 		printf("%s: transfer error, downgrading to DMA mode %d\n",
 		    drv_dev->dv_xname, drvp->DMA_mode);
-	} else if (drvp->drive_flags & DRIVE_DMA) {
-		drvp->drive_flags &= ~DRIVE_DMA;
+	} else if (drvp->drive_flags & (DRIVE_DMA | DRIVE_UDMA)) {
+		drvp->drive_flags &= ~(DRIVE_DMA | DRIVE_UDMA);
 		drvp->PIO_mode = drvp->PIO_cap;
 		printf("%s: transfer error, downgrading to PIO mode %d\n",
 		    drv_dev->dv_xname, drvp->PIO_mode);
diff --git a/sys/dev/ic/wdcreg.h b/sys/dev/ic/wdcreg.h
index aae1105e770c..502f8e6118bc 100644
--- a/sys/dev/ic/wdcreg.h
+++ b/sys/dev/ic/wdcreg.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: wdcreg.h,v 1.21 1999/01/18 20:06:25 bouyer Exp $	*/
+/*	$NetBSD: wdcreg.h,v 1.22 1999/03/07 14:02:54 bouyer Exp $	*/
 
 /*-
  * Copyright (c) 1991 The Regents of the University of California.
@@ -83,6 +83,7 @@
  * Error bits.
  */
 #define	WDCE_BBK	0x80	/* bad block detected */
+#define	WDCE_CRC	0x80	/* CRC error (Ultra-DMA only) */
 #define	WDCE_UNC	0x40	/* uncorrectable data error */
 #define	WDCE_MC		0x20	/* media changed */
 #define	WDCE_IDNF	0x10	/* id not found */
@@ -90,7 +91,6 @@
 #define	WDCE_ABRT	0x04	/* aborted command */
 #define	WDCE_TK0NF	0x02	/* track 0 not found */
 #define	WDCE_AMNF	0x01	/* address mark not found */
-#define WDERR_BITS	"\020\010bbk\007unc\006mc\005idnf\004mcr\003abrt\002tk0nf\001amnf"
 
 /*
  * Commands for Disk Controller.