AM79C978VCSLASHW datasheet(42/261 Pages) AMD

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Am79C978

Figure 12.

Slave Cycle Data Parity Error Response

Master Bus Interface Unit

The master Bus Interface Unit (BIU) controls the acqui-

sition of the PCI bus and all accesses to the initializa-

tion block, descriptor rings, and the receive and

transmit buffer memory. Table 7 shows the usage of

PCI commands by the Am79C978 controller in master

mode.

Bus Acquisition

The microcode will determine when a DMA transfer

should be initiated. The first step in any bus master

transfer is to acquire ownership of the bus. This task is

handled by synchronous logic within the BIU. Bus own-

ership is requested with the REQ signal and ownership

is granted by the arbiter through the GNT signal.

Figure 13 shows the Am79C978 controller bus acquisi-

tion. REQ is asserted and the arbiter returns GNT while

ano ther bu s m a st er is tra n s f er ri ng d a ta. T h e

Am79C978 controller waits until the bus is idle

(FRAME and IRDY deasserted) before it starts driving

AD[31:0] and C/BE[3:0] on clock 5. FRAME is asserted

at clock 5 indicating a valid address and command on

AD[31:0] and C/BE[3:0]. The Am79C978 controller

does not use address stepping which is reflected by

FRAME

CLK

IRDY

TRDY

C/BE

DEVSEL

PAR

ADDR

CMD

PAR

2345678

DATA

PAR

PERR

22206B-15

Table 7.

Master Commands

C[3:0]

Command

Use

0000

Interrupt

Acknowledge

Not used

0001

Special Cycle

Not used

0010

I/O Read

Not used

0011

I/O Write

Not used

0100

Reserved

0101

Reserved

0110

Memory Read

Read of the initialization

block and descriptor

rings

Read of the transmit

buffer in non-burst mode

0111

Memory Write

Write to the descriptor

rings and to the receive

buffer

1000

Reserved

1001

Reserved

1010

Configuration Read

Not used

1011

Configuration Write

Not used

1100

Memory Read

Multiple

Read of the transmit

buffer in burst mode

1101

Dual Address Cycle Not used

1110

Memory Read Line

Read of the transmit

buffer in burst mode

1111

Memory Write

Invalidate

Not used

Table 7.

Master Commands (Continued)

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