Buffer Descriptors

 

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Offset + 0

R

TO1

W

TO2

L

TC

ABC

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Offset + 2

 

 

 

 

 

 

 

Data Length

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Offset + 4

Tx Data Buffer Pointer - A[31:16]

 

Offset + 6

Tx Data Buffer Pointer - A[15:0]

Figure 17-28. Transmit Buffer Descriptor (TxBD)

Table 17-37. Transmit Buffer Descriptor Field Definitions

Word

Location

Field Name

 

Description

 

 

 

 

Offset + 0

Bit 15

R

Ready. Written by the FEC and the user.

 

 

 

0

The data buffer associated with this BD is not ready for

 

 

 

 

transmission. The user is free to manipulate this BD or its

 

 

 

 

associated data buffer. The FEC clears this bit after the

 

 

 

 

buffer has been transmitted or after an error condition is

 

 

 

 

encountered.

 

 

 

1

The data buffer, which has been prepared for transmission

 

 

 

 

by the user, has not been transmitted or is currently being

 

 

 

 

transmitted. No fields of this BD may be written by the user

 

 

 

 

once this bit is set.

 

 

 

 

Offset + 0

Bit 14

TO1

Transmit software ownership. This field is reserved for software

 

 

 

use. This read/write bit will not be modified by hardware, nor will

 

 

 

its value affect hardware.

 

 

 

 

Offset + 0

Bit 13

W

Wrap. Written by user.

 

 

 

0

The next buffer descriptor is found in the consecutive

 

 

 

 

location

 

 

 

1

The next buffer descriptor is found at the location defined in

 

 

 

 

ETDSR.

 

 

 

 

Offset + 0

BIt 12

TO2

Transmit software ownership. This field is reserved for use by

 

 

 

software. This read/write bit will not be modified by hardware,

 

 

 

nor will its value affect hardware.

 

 

 

 

Offset + 0

Bit 11

L

Last in frame. Written by user.

 

 

 

0

The buffer is not the last in the transmit frame.

 

 

 

1

The buffer is the last in the transmit frame.

 

 

 

 

Offset + 0

Bit 10

TC

Tx CRC. Written by user (only valid if L = 1).

 

 

 

0

End transmission immediately after the last data byte.

 

 

 

1

Transmit the CRC sequence after the last data byte.

 

 

 

 

Offset + 0

Bit 9

ABC

Append bad CRC. Written by user (only valid if L = 1).

 

 

 

0

No effect

 

 

 

1

Transmit the CRC sequence inverted after the last data byte

 

 

 

 

(regardless of TC value).

 

 

 

 

Offset + 0

Bits [8:0]

Reserved.

 

 

 

 

 

17-50

MCF5282 User’s Manual

MOTOROLA

Page 406
Image 406
Motorola MCF5282, MCF5281 user manual TO1 TO2 ABC