I've observed a condition where the esp driver will semi-randomly get
timeouts.  It appears that this is due to a race condition in the TC
DMA code that will occasionally cause an interrupt to be lost.

If you've had problems like this, please try the following patch:

Index: tcds_dma.c
===================================================================
RCS file: /cvsroot/src/sys/arch/alpha/tc/tcds_dma.c,v
retrieving revision 1.6.4.1
diff -c -2 -r1.6.4.1 tcds_dma.c
*** tcds_dma.c	1996/09/10 17:28:19	1.6.4.1
--- tcds_dma.c	1996/12/04 21:52:21
***************
*** 67,74 ****
--- 67,78 ----
  	int x;
  
+ #if 0
  	x = tcds_scsi_isintr(sc, 0);
  
  	/* Clear the TCDS interrupt bit. */
  	(void)tcds_scsi_isintr(sc, 1);
+ #else
+ 	x = tcds_scsi_isintr(sc, 1);
+ #endif
  
  	/* XXX */