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An Address Caching Mechanism for an Off-Chip Serial Bus

IP.com Disclosure Number: IPCOM000022648D
Original Publication Date: 2004-Mar-23
Included in the Prior Art Database: 2004-Mar-23
Document File: 2 page(s) / 18K

Publishing Venue

IBM

Abstract

This article presents an address caching mechanism that reduces the memory and I/O access latency over a serial link.

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An Address Caching Mechanism for an Off -Chip Serial Bus

Disclosed is a caching mechanism for memory and I/O accesses over a serial connection. With the cache memories placed at the sending and receiving ends, the address field of payload in the packet is compressed and decompressed to shorten the access latency.

The mechanism is based on the fact that memory and I/O accesses have temporal and spatial locality in address references. Higher order portions of the address are cached in the base address cache and base address array, and transferred in a compressed form over the serial bus, as shown in Figure 1.

Base address cache

Base address array

Serial bus

Division position Division position

Figure 1. Address caching and compression

The division position, which defines how many higher order bits are cached, can be arbitrarily settled, because a serial bus is flexible in terms of the packet length. It even can be moved on the fly by sending special packet dedicated to the division position control.

High order address bits

Low order address bits

High order address bits

Low order address bits

Address

I/O device 3

FFFFFFFF

FFFF0000

Nothing

mapped

9000003F

I/O device 2

90000000

Nothing mapped

I/O device 1

800000FF

80000000

Nothing mapped

Memory

00FFFFFF

00000000

Memory map

1

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Base address cache Base address array

Figure 2. Memory address map and caching scheme

Figure 2 is an example of a typical addr...