Chapter 12: 10/100 IEEE802.3 Media Access Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
12-38
The buffer address must be 8-byte aligned while the Descriptor address must be 16-byte
aligned.
12.4.2 Receive
Descriptors
The format of the Receive Descriptors is shown below. It is made of two double-words, and
the fields are described in more detail in Table 12-34.
63
0
OWN
Byte-Count Buffer 1
Byte-Count Buffer 2
Control Bits
Status Bits
Buffer Address 1
Buffer Address 2
Figure 12-7 Receive Descriptor Format
12.4.2.1 Receive
Descriptor
The Receive Descriptor contains the receive frame status, the frame length, and the
Descriptor ownership information in the first word (Word 0). The 32 bits of two Receive
Buffer Addresses is in the second word (Word 1). Bits [31:0] in Word 0 are read only. Bits
[30:0] are valid only when RxEOF is set.
Table 12-34 Receive Descriptor Field Descriptions
Word 0 Fields
Bit(s)
Field
Description
63
OWN
When set, indicates that the Descriptor is owned by the MAC. When reset, indicates that
the Descriptor is owned by the C790. MAC clears this bit either when it completes the
frame reception or when the buffers that are associated with this Descriptor are full.
62:59
-
Must be set to “0”.
58:48
Buffer1 Size
Indicates the size in bytes of the first data buffer. If this field is zero, the MAC ignores this
buffer and only uses buffer 2.
The buffer size should be a multiple of 8. If it is not, the least three bits are ignored.
47:37
Buffer2 Size
Indicates the size in bytes of the second data buffer. If RxChain is set (Address Chained),
the MAC ignores this buffer and fetches the next Descriptor.
36
RxERing
Receive End of Ring
When set, indicates that the Descriptor pointer has reached its final Descriptor, and the
MAC returns to the base address of the list, creating a Descriptor ring.
35
RxChain
Second Address Chained
When set, indicates that the second address in the Descriptor is the next Descriptor
address rather than the second buffer address. If RxERing is set, then RxChain is
ignored.
34
RxSOF
Start of Frame
When set, indicates that this Descriptor contains the first byte of a frame.
33
RxEOF
End of Frame
When set, indicates that this Descriptor contains the last byte of a frame. If this bit is not
set, all frame status bits are invalid except the OWN bit.
32:31
–
Reserved
30:20
RxFrmLen
Receive Frame Length
19
RxNoCRC
Strip CRC
18
RxDType
Receive Data Type
0 : External frame
1 : Internal loop-back frame
17
RxFF
Receive Frame Filter Fail
When set, indicates that the frame failed the address recognition filtering. This bit can be
set only when the MAC is in the promiscuous mode (RxAll bit is set in RFCReg).
16:15
RxFrmType
Receive Frame Type
Word 0
Word 1
Summary of Contents for TMPR7901
Page 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Page 14: ...Handling Precautions ...
Page 15: ......
Page 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Page 41: ...4 Precautions and Usage Considerations 4 2 ...
Page 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
Page 43: ......
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