Browse Prior Art Database

RAM Filter to Avoid Interrupt Chaining through ROM

IP.com Disclosure Number: IPCOM000113108D
Original Publication Date: 1994-Jul-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Deckys, DJ: AUTHOR [+4]

Abstract

Disclosed is the addition of a "filter" to system RAM code in a computer system having an adapter which has chained interrupt vectors through adapter ROM code. The filter determines whether the service code for a call resides in the adapter ROM interrupt service routine, or in the system RAM interrupt service routine, and routes the call accordingly.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 75% of the total text.

RAM Filter to Avoid Interrupt Chaining through ROM

      Disclosed is the addition of a "filter" to system RAM code in a
computer system having an adapter which has chained interrupt vectors
through adapter ROM code.  The filter determines whether the service
code for a call resides in the adapter ROM interrupt service routine,
or in the system RAM interrupt service routine, and routes the call
accordingly.

      Code stored in an adapter ROM memory usually provides new
functions, or enhances current functions, by chaining BIOS or DOS
interrupt vectors through the adapter ROM memory, where the interrupt
service routine for these new functions is located, to system RAM
memory.  Even interrupt vectors not requiring this new service
routine are handled in this way.  However, the execution of code from
an adapter ROM memory is much slower than the execution of code
through system RAM, since the execution of adapter ROM code requires
access through the I/O channel, such as the Micro Channel* bus, and
since ROM access generally requires more time than RAM access.
Furthermore, in a system implementing cache memory on a local bus,
each access to a memory without cache, such as memory accessed
through the I/O channel, causes a cache miss.

      As shown in the Figure, these problems are minimized by
directing an interrupt vector 10 to a "filter" interrupt service
routine 12 added to system RAM 14, so that a decision is made at
block 16 concerning whether the service...