Browse Prior Art Database

I/O Address Protection Implementation

IP.com Disclosure Number: IPCOM000109006D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Bansal, A: AUTHOR

Abstract

Disclosed is a process that allows a processor to check the range for an I/O address against specified bounds. The process allows the I/O protection logic to be bypassed for privileged and memory access instructions. Keys to Operation:

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 93% of the total text.

I/O Address Protection Implementation

       Disclosed is a process that allows a processor to check
the range for an I/O address against specified bounds.  The process
allows the I/O protection logic to be bypassed for privileged and
memory access instructions.  Keys to Operation:

      The figure shows a block diagram of the logic configuration.
      A.   Carry Save Adders and Block Carry Look Ahead technique
provides a quick addition of the input address and string count and a
comparison with the upper bound.
      B.   Range check is bypassed for all memory accesses and
privileged mode instructions.
      C.   The process also prevents an I/O string instruction from
exceeding the upper bound.
Operation Sequence:

      16-bit input address is compared in parallel with the upper and
lower bound.

      If C_U, the block carry output from the upper bound comparison
is equal to 0, then input address plus string count plus 1 are less
than or equal to the upper bound or else the range check is
activated.

      If C_L, the block carry output from the lower bound comparison
is equal to 0, then the input address is greater than the lower
limit.  The input address is equal to the lower bound if SUM_L, the
sum output of the block carry look ahead is equal to 0 and C_L, the
carry out is equal to 1.
Applications:

      The disclosed process allows an I/O processor to check the
input address against the upper and lower bound and t...