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.