CS5920 datasheet(25/160 Pages) AMCC

25 / 160 page

S5920 – PCI Product

Revision 1.01 – November 28, 2005

AMCC Confidential and Proprietary

DS1596

Data Book

MAILBOX OPERATION

The mailbox registers are divided into two 4-byte sets.

Each set is dedicated to one bus for data transfer to

the other bus. Figure 3 shows a block diagram of the

mailbox section of the S5920. The provision of mailbox

registers provides data or user defined command/sta-

tus transfer capability between two buses. An empty/

full indication for each mailbox register, at the byte

level, is determined by polling a status register acces-

sible to both the PCI and Add-On buses. Providing

mailbox byte level full indications allows greater flexi-

bility in 8-, 16-or 32-bit designs; i.e., transferring a

single byte in 8-bit Add-On bus without requiring the

assembly or disassembly of 32-bit data.

A mailbox byte level interrupt feature for PCI or Add-

On buses is provided. Bit locations configured within

the S5920 operation registers can select which mail-

box byte is to generate an interrupt when the mailbox

is written to. Interrupts can be generated to the PCI or

Add-On buses. PCI bus interrupts may also be gener-

ated from direct hardware interfacing due to a unique

S5920 feature. The Add-On mailbox is hardware

accessible via a set of dedicated device pins. A single

load pulse latches data into the mailbox generating an

interrupt, if enabled.

PASS-THRU OPERATION

Pass-Thru region accesses can execute PCI bus

cycles in real time or through an internal FIFO. Real

time operation allows the PCI bus to directly read or

write to Add-On bus resources. The S5920 allows the

designer to declare up to four individual Pass-Thru

regions. Each region may be defined as 8, 16 or 32

bits wide, mapped into memory or I/O system space

and may be up to 512 MB in size. Figure 4 shows a

ba sic b l ock diag ra m of the S592 0 Pass-T h ru

architecture.

Host communications to the Pass-Thru data channel

utilizes dedicated Add-On bus pins to signal that a PCI

read or write has been requested. User logic decodes

these signals to determine if it must read or write data

to the S5920 to satisfy the PCI request. Information

decoded includes: PCI read/write transaction request,

the byte lanes involved, the specific Pass-Thru region

accessed and whether the request is a burst or single

cycle access.

Pass-Thru operation supports single PCI data cycles

and PCI data bursts. During PCI burst operations, the

S5920 is capable of transferring data at the full PCI

bandwidth. Should slower Add-On logic be imple-

mented, the S5920 will issue a PCI bus retry until the

requested transfer is completed.

Figure 4. Mailbox Block Diagram

Mailbox

Byte 0

Mailbox

Byte 1

Mailbox

Byte 2

Mailbox

Byte 3

Mailbox Status

Mailbox

Byte 0

Mailbox

Byte 1

Mailbox

Byte 2

Mailbox

Byte 3

Add-On

Decode

Control

PCI

Decode

Control

CS5920 Datasheet(PDF) 25 Page - Applied Micro Circuits Corporation

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