The two examples were with GENERIC kernel,
mef> trap type 200 at 34d2d8
mef> trap type 200 at 34d2d8

With install kernel (as of 20020526), I got:
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 5 (Ultra/100)
trap type 200 at 91c9dc

and the location looks to me with 
objdump -d ./INSTALL/netbsd:

0091c914 <pdc202xx_setup_channel>:
  ....
  91c9cc:       81 7d 00 ac     lwz     r11,172(r29)
  91c9d0:       7d 29 00 30     slw     r9,r9,r0
  91c9d4:       7f 6b 48 ae     lbzx    r27,r11,r9
  91c9d8:       7c 00 06 ac     eieio
> 91c9dc:       7c 00 04 ac     sync
  91c9e0:       80 7d 00 98     lwz     r3,152(r29)
  91c9e4:       80 9d 00 9c     lwz     r4,156(r29)
  91c9e8:       38 a0 00 50     li      r5,80
  91c9ec:       4b ff 04 0d     bl      90cdf8 <pci_conf_read>

which somewhere arround in sys/dev/pci/pciide.c:
   3658 pdc202xx_setup_channel(chp)
   .....
   3678         /* Per channel settings */
   3679         if (PDC_IS_262(sc)) {
   3680                 scr = bus_space_read_1(sc->sc_dma_iot, sc->sc_dma_ioh,
   3681                     PDC262_U66);
   3682                 st = pci_conf_read(sc->sc_pc, sc->sc_tag, PDC2xx_STATE);
   3683                 /* Trim UDMA mode */
 
Does it make sense ?
---
Makoto Fujiwara, 
Chiba, Japan, Narita Airport and Disneyland prefecture.