AM79C978AVCW datasheet(45/256 Pages) AMD

45 / 256 page

Am79C978A

Figure 19.

Disconnect Without Data Transfer

RTABORT (PCI Status register, bit 12) will be set to

indicate that the Am79C978A controller has received a

target abort. In addition, SINT (CSR5, bit 11) will be set

to 1. When SINT is set, INTA is asserted if the enable

bit SINTE (CSR5, bit 10) is set to 1. This mechanism

can be used to inform the driver of the system error. The

host can read the PCI Status register to determine the

exact cause of the interrupt.

Master Initiated Termination

There are three scenarios besides normal completion

of a transaction where the Am79C978A controller will

terminate the cycles it produces on the PCI bus.

Preemption During Non-Burst Transaction

When the Am79C978A controller performs multi-

ple non-burst transactions, it keeps REQ asserted

until the assertion of FRAME for the last transac-

tion. When GNT is removed, the Am79C978A con-

troller will finish the current transaction and then

release the bus. If it is not the last transaction,

REQ will remain asserted to regain bus ownership

as soon as possible. See Figure 21.

Preemption During Burst Transaction

When the Am79C978A controller operates in burst

mode, it only performs a single transaction per bus

mastership period, where transaction is defined as one

address phase and one or multiple data phases. The

central arbiter can remove GNT at any time during the

transaction. TheAm79C978A controller will ignore the

deassertion of GNT and continue with data transfers,

as long as the PCI Latency Timer is not expired. When

the Latency Timer is 0 and GNT is deasserted, the

Am79C978A controller will finish the current data

phase, deassert FRAME, finish the last data phase,

and release the bus. If EXTREQ (BCR18, bit 8) is

cleared to 0, it will immediately assert REQ to regain

bus ownership as soon as possible. If EXTREQ is set

to 1, REQ will stay asserted.

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

REQ

GNT

PAR

DEVSEL is sampled

STOP

ADDRi

0000

0111

PAR

0111

3456789

ADDRi

DATA

PAR

22399A-22

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