AM79C970 datasheet(122/168 Pages) AMD

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P R E L I M I N A R Y

AMD

1-989

Am79C970

Initialization Block

When SSIZE32=0 (BCR20, bit 8), then the software

structures are defined to be 16 bits wide. The base ad-

dress of the Initialization block in this mode must be

aligned to a WORD boundary, i.e. CSR1, bit 0 and

CSR16, bit 0 must be set to ZERO. When SSIZE32 = 0,

the initialization block looks like Table 13.

Note that the PCnet-PCI device performs DWORD ac-

cesses to read the initialization block. This statement is

always true, regardless of the setting of the SSIZE32 bit.

When SSIZE32=1 (BCR20, bit 8), then the software

structures are defined to be 32 bits wide. The base ad-

dress of the Initialization block in this mode must be

aligned to a DOUBLE WORD boundary, i.e., CSR1, bits

0 and 1 and CSR16, bits 0 and 1 must be set to ZERO.

When SSIZE32 = 1, the initialization block looks like

Table 14.

Table 13. 16-Bit Data Structure Initialization Block

Address

Bits 15–13

Bit 12

Bits 11–8

Bits 7–4

Bits 3–0

IADR+00h

MODE 15–00

IADR+02h

PADR 15–00

IADR+04h

PADR 31–16

IADR+06h

PADR 47–32

IADR+08h

LADRF 15–00

IADR+0Ah

LADRF 31–16

IADR+0Ch

LADRF 47–32

IADR+0Eh

LADRF 63–48

IADR+10h

RDRA 15–00

IADR+12h

RLEN

RES

RDRA 23–16

IADR+14h

TDRA 15–00

IADR+16h

TLEN

RES

TDRA 23–16

Table 14. 32-Bit Data Structure Initialization Block

Bits

Address

31–28

27–24

23–20

19–16

15–12

11–8

7–4

3–0

IADR+00h

TLEN

RES

RLEN

RES

MODE

IADR+04h

PADR 31–00

IADR+08h

RES

PADR 47–32

IADR+0Ch

LADR 31–00

IADR+10h

LADR 63–32

IADR+14h

RDRA 31–00

IADR+18h

TDRA 31–00

RLEN and TLEN

When SSIZE32=0 (BCR20, bit 8), then the software

structures are defined to be 16 bits wide, and the RLEN

and TLEN fields in the initialization block are 3 bits wide,

occupying bits 15, 14, and 13, and the value in these

fields determines the number of Receive and Transmit

Descriptor Ring Entries (DRE) which are used in the de-

scriptor rings. Their meaning is as follows:

R/TLEN

# of DREs

000

001

010

011

100

101

110

111

128

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