lan9420 Standard Microsystems Corp., lan9420 Datasheet - Page 45

• Manufacturer Part Number: lan9420
• Description: Lan9420/lan9420i Single-chip Ethernet Controller With Hp Auto-mdix Support And Pci Interface
• Manufacturer: Standard Microsystems Corp.

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
SMSC LAN9420/LAN9420i
TDES0
TDES2
TDES3
TDES1
3.4.2.2
BITS
31:0
OW
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
IC LS FS R
Receive Descriptor 3 (RDES3)
Transmit descriptors
The descriptors must be 4-DWORD (16-byte) aligned, while there are no alignment restrictions on
transmit buffer addresses. Providing two buffers, two byte-count buffers, and two address pointers in
each descriptor facilitates compatibility with various types of memory-management schemes.
Figure 3.17
Buffer 2 Address Pointer (Next Descriptor Address)
The RCH (Second Address Chained) bit (RDES1[24]) determines the usage of this field as
follows:
RCH is zero: This field contains the pointer to the address of buffer 2 in Host memory. The buffer
must be DWORD (32-bit) aligned (RDES3[1:0] = 00b). In the case where the buffer is not
DWORD aligned, the resulting behavior is undefined.
RCH is one: Descriptor chaining is in use and this field contains the pointer to the next descriptor
in Host memory. The descriptor must be 4-DWORD (16-byte) aligned (RDES3[3:0] = 0000b). In
the case where the buffer is not 4-DWORD aligned, the resulting behavior is undefined.
Note:
Host Actions: Initializes this field.
DMAC Actions: Reads this field upon opening a new DMA descriptor to obtain the buffer
address.
CK
shows the Transmit Descriptor format.
If RER (RDES1[25]) is set, RCH is ignored and this field is treated as a pointer to buffer
2 as in the “RCH is zero” case above.
AC TE TC DP R
RESERVED
Figure 3.17 Transmit Descriptor
Table 3.8 RDES3 Bit Fields
DATASHEET
BUFFER 1 ADDRESS POINTER
BUFFER 2 ADDRESS POINTER
45
DESCRIPTION
TBS2
ES
RES
LC NC LT EC HF
TBS1
Revision 1.1 (03-31-08)
CC
ED UE DE