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1991-08-26
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Tech Tip #98.011
03/20/91
Problem:
Cards like the Serial Intelligent Controllers, Computone/Digiboard
etc., require 64k/128k, etc. of non-cache area. What should be the
address setting for these cards on the Enterprise, EISA boards?
Solution:
On the MKIII AT boards, the 14-15Mb region was defined as non-cache,
ie. if the physical memory present on the motherboard is less than
14Mb, then any I/O card could use this area to map its dual ported
memory.
On the Enterprise boards the non-cached area is dynamically
allocated by the BIOS, by default the memory region from the top of
the physical memory to the 4 Gigabyte boundary is not cached.
There can be two possible situations:
I. EISA I/O Card:
If the Serial Intelligent Controller is EISA, then it can
address upto 4 Gigabytes of physical memory. So these
cards can be configured at locations below 2-3 Gigabytes,
and then these locations could be made non-cached by using
the ECU. On the Enterprise board, any location in the
memory can be defined as Non-cached, and this is possible
in the 256k granularity.
II. ISA I/O Cards:
If the Serial Intelligent Controller is ISA then it can
address upto 16 Megabytes of physical memory. This means
that these cards must be located below the 16 Megabyte
boundary, and there should not be any physical memory in
that location. If these conditions are met, then the BIOS
will make the location non-cached by default.
|-----A-----|-----B-----|---------------C---------------|
I-----------I-----------I--------------------//---------I
0Mb 4Mb 16Mb 4Gb
| | |
| | |
Physical Memory | |
(for example) | EISA Cards
|
ISA Cards
A: EISA/ISA Cards cannot be configured here.
B: EISA/ISA Cards can be configured here.
C: EISA Cards can be configured here.