AFAIK, the A25000 (aka A2052), it's an auto-configuring card with just 2Mb of RAM in it.
Hardly this is a font of problems.
The jumpers probably are there for test purposes only (or for disable half of the memory).
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For the A2091, there a lot of information (taken from The Big Book of Amiga Hardware :
Jumpers
JP1: Memory Size
0K: Set for no memory.
512K: Set for 512K of RAM.
1M: Set for 1M of RAM.
2M: Set for 2M of RAM.
JP2: Autoboot Enable
AUTO: Set to enable autobooting from the A2091.
DIS: Set to disable autobooting from the A2091.
JP3: Interrupt Select
INT6: Select interrupt 6.
INT2: Select interrupt 2.
JP5: Options
Option 1: LUN Enable. When jumpered, enables scanning for Logical
Unit Numbers numbers at each physical SCSI address.
Default value: Off.
Option 2: Time-Out Length. When jumpered, enables longer time-out
for slow-starting drives. Default: Off. (Note: When on,
this jumper disables parity during the message in phase.)
Option 3: Reserved. Factory default: Off.
JP201: Factory use only.
The version 7 ROM fixes the following bugs in the 6.6 ROM
- >1GB HD support
- DMA reselection bug fixed
- disconnect/reconnect performance improved a lot
- Sync messages are handled
- Error handling improved
- Sync problems with Seagate/Syquest fixed
- Removable media recognition fixed
- Slow boot jumper now does a 15 second wait plus 300ms scan
More complete information can be found in
TBBoAH.
