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Method for Accessing Non-Bursting Regions in Local Bus Address Space without Pre-Fetching

IP.com Disclosure Number: IPCOM000111955D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 90K

Publishing Venue

IBM

Related People

Farrell, JK: AUTHOR [+6]

Abstract

Disclosed is a method for preventing the corruption of data in self-clearing registers residing in a particular area of the memory map of the CFE (Common Front End) bus architecture, which defines a high-performance, synchronous bus. The normal mode of transfer on the CFE bus is the bursting of data, which implies a single address followed by successive data transfers. To improve the overall throughput of a device residing on the CFE local bus. the prefetching of read data is performed. The Micro Channel* Interface Chip performs both bursting and prefetching transfers for read accesses of the Micro Channel bus.

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This is the abbreviated version, containing approximately 52% of the total text.

Method for Accessing Non-Bursting Regions in Local Bus Address Space
without Pre-Fetching

      Disclosed is a method for preventing the corruption of data in
self-clearing registers residing in a particular area of the memory
map of the CFE (Common Front End) bus architecture, which defines a
high-performance, synchronous bus.  The normal mode of transfer on
the CFE bus is the bursting of data, which implies a single address
followed by successive data transfers.  To improve the overall
throughput of a device residing on the CFE local bus.  the
prefetching of read data is performed.  The Micro Channel* Interface
Chip performs both bursting and prefetching transfers for read
accesses of the Micro Channel bus.

      However, the CFE bus architecture has defined an address range
in local bus address space where non-bursting local bus slaves
reside.  Typically, this non-bursting region is occupied by banks of
registers from each chip residing on the local bus.  These banks of
registers often include status registers that are self-clearing on a
read operation.  A Micro Channel slave that performs prefetching of
data on the local bus can inadvertently corrupt the data in
self-clearing registers by reading more than the number of words
requested by the Micro Channel master.

      Prefetching on the local bus is disabled when the Micro Channel
interface chip is accessed as a slave on the Micro Channel through
its I/O data port mechanism, if the local bus address falls into the
non-bursting region defined by the CFE architecture.  Accesses to the
non-bursting region of the local bus through the shared memory window
of the Micro Channel occur with prefetching enabled.  Thus, the Micro
Channel interface chip has two separate mechanisms to access the
non-bursting region of the local address space, while dynamically
switching between prefetching enabled and disabled states, based on
the address ranges specified and on the Micro Channel access method.

      The Micro Channel interface chip uses a non-streaming Micro
Channel I/O data slave port mechanism to perform non-prefetching
reads of the non-burst region of the local bus, as defined by the CFE
bus architecture.  For example, the non-bursting local bus address
region is defined from address 0000 0000 to 1FFF FFF...