NEC Network Controller uPD98502 - Manual (Page 346)

CHAPTER 6 USB CONTROLLER
346 Preliminary User’s Manual S15543EJ1V0UM
Figure 6-14. Receive Descriptor Configuration
-R x B uffer D irectory
B uffer D irectory A ddress
-R x Link P ointer
0
31 0
|
B uffer D esciptor N
B uffer D esciptor 4
B uffer D esciptor 3
B uffer D esciptor 2
B uffer D esciptor 1
B uffer D esciptor 0
Link P ointer
-R x B uffer D escriptor
31 0 16 15
B uffer A ddress
R eserved S ize L 1
30
R eserved
29
0
31 0 16 15 30 29
Rx Buffer Directory: A Rx Buffer Directory. This is composed of buffer descriptors and a link pointer. A single
Rx Buffer Directory can contain up to 255 buffer descriptors.
Rx Buffer Descriptor: Contains the Rx buffer data.
When Bit31 (Last bit) is set to a ‘1’, that Buffer Descriptor indicates the last buffer in the
pool.
Bit30 is used to discriminate between the Buffer Descriptor and Link Pointer. When set to
1, this bit indicates the Buffer Descriptor.
The "Size" field indicates the buffer size. As the buffer size, a value between 1 and 65535
bytes can be set. The "Buffer Address" field indicates the start address of the buffer.
Rx Link Pointer: This is the link pointer. It indicates the last Buffer Directory.
Bit31 is set to 0.
Bit30 is used to discriminate between the Buffer Descriptor and Link Pointer. When set to
0, this bit indicates the Link Pointer.
The "Buffer Directory Address" field indicates the start address of the next Buffer
Directory.