Figure 20-3. Enhanced Transmit Descriptor Structure
31
0
7
23
15
Status [16:7]
Byte Count Buffer 1 [12:0]
Byte Count Buffer2 [28:16]
TDES0
TDES1
TDES2
TDES3
Buffer1 Address [31:0]
Buffer2 Address [31:0]/Next Descriptor Address [31:0]
OWN
Transmit Timestamp High [31:0]
Transmit Timestamp Low [31:0]
Reserved
Reserved
CTRL
[30:26]
T
T
S
E
CTRL
[24:18]
T
T
S
S
CTRL/
Status
[6:3]
Status
[2:0]
CTRL
[31:29]
Reserved
TDES4
TDES5
TDES6
TDES7
The following tables define the Enhanced Transmit Descriptors. Transmit Descriptor 0 (TDES0)
contains the transmitted frame status and the descriptor ownership information. TDES1 contains
the buffer sizes and other bits which control the descriptor chain or ring and the frame being
transferred. TDES2 contains the address pointer to the first buffer of the descriptor. TDES3 contains
the address pointer either to the second buffer of the descriptor or the next descriptor. TDES6 and
TDES7 contain the timestamp.
Table 20-2. Enhanced Transmit Descriptor 0 (TDES0)
Description
Bit
OWN: Own Bit
When set, this bit indicates that the descriptor is owned by the DMA. When this bit is reset, it indicates that the
descriptor is owned by the Host. The DMA clears this bit either when it completes the frame transmission or when
the buffers allocated in the descriptor are empty. The ownership bit of the First Descriptor of the frame should
be set after all subsequent descriptors belonging to the same frame have been set. This avoids a possible race
condition between fetching a descriptor and the driver setting an ownership bit.
31
IC: Interrupt on Completion
When set this bit sets the Transmit Interrupt (TI) bit in the EMACDMARIS register when the frame contained in
this descriptor has been transmitted.
30
June 18, 2014
1414
Texas Instruments-Production Data
Ethernet Controller