Browse Prior Art Database

Complete-Image Update Methodology for Single Device, Read Only Memory-Executed Microcode

IP.com Disclosure Number: IPCOM000118883D
Original Publication Date: 1997-Aug-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 95K

Publishing Venue

IBM

Related People

Hamilton, RA: AUTHOR [+3]

Abstract

Disclosed is a method for flash updating an entire Electronically-Programmable Read-Only Memory (EPROM), including its recovery block.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Complete-Image Update Methodology for Single Device, Read Only Memory-Executed
Microcode

      Disclosed is a method for flash updating an entire
Electronically-Programmable Read-Only Memory (EPROM), including its
recovery block.

      As a service and maintenance issue, it is often desirable to
update microcode without physical removal of the chip on which it is
housed.  Such a capability, called a "Flash Update," involves
downloading (through a variety of means) new microcode into a storage
device called  an EPROM.  This technique has been used for several
years and is applicable to many electronics devices, including
computers.  Note that  in this discussion, EPROM is used along with
Read-Only Memory (ROM). ROM  refers to the type of memory found on
the chip, and EPROM refers to the  chip itself.

      Often, a portion of the microcode residing on the EPROM is
required to remain operative at all times to facilitate the flash
update process.  This portion, called the "recovery" section is
usually not capable of being updated, unless additional complexity
and expense is added by running the entire microcode out of Random
Access Memory (RAM).  However, for cost purposes, many designers
choose not to load code into RAM for execution, but rather run
straight from the EPROM, thus  losing their means of updating the
microcode "recovery" section. Running  instructions from ROM and
giving up the complete update capability means  that only a small
amount of RAM is needed for static and dynamic data allocation.

      This presents a design tradeoff.  By cutting costs and
minimizing RAM usage, the engineer loses the ability to modify
recovery code after the device has shipped to the customer.  In the
event that a  programming error (for example) is found in this part
of the code, no options remain except for the expensive and
time-consuming physical replacement of the chip in the field.

      The specific problem which this paper discusses is this
tradeoff.  It discusses a methodology to update the complete
microcode image, including the previously-permanent recovery portion,
without resorting to exclusive RAM execution, thus providing
flexibility while  mitigating hardware complexity and minimizing
design costs.

      It should be noted that when an EPROM is put into "write mode",
the program instructions which update it must be fetched from another
memory device, usually RAM.  In the following discussion, the code
which downloads the data (in our particular case, in blocks of 256
bytes) is  executed out of ROM and stores the data in RAM.  The
program then loads  a small copy routine into RAM which does the
actual writing of the EPROM.

      EPROMs consist of "sectors" or building blocks of memory into
which microcode programs can be loaded...