RM0090 Rev 18 1175/1749
RM0090 Ethernet (ETH): media access control (MAC) with DMA controller
1239
• TDES2: Transmit descriptor Word2
TDES2 contains the address pointer to the first buffer of the descriptor or it contains
time stamp data.
• TDES3: Transmit descriptor Word3
TDES3 contains the address pointer either to the second buffer of the descriptor or the
next descriptor, or it contains time stamp data.
28:16 TBS2: Transmit buffer 2 size
These bits indicate the second data buffer size in bytes. This field is not valid if TDES0[20] is
set.
15:13 Reserved, must be kept at reset value.
12:0 TBS1: Transmit buffer 1 size
These bits indicate the first data buffer byte size, in bytes. If this field is 0, the DMA ignores
this buffer and uses Buffer 2 or the next descriptor, depending on the value of TCH
(TDES0[20]).
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
TBAP1/TBAP/TTSL
rw
Bits 31:0 TBAP1: Transmit buffer 1 address pointer / Transmit frame time stamp low
These bits have two different functions: they indicate to the DMA the location of data in
memory, and after all data are transferred, the DMA can then use these bits to pass back time
stamp data.
TBAP: When the software makes this descriptor available to the DMA (at the moment that the
OWN bit is set to 1 in TDES0), these bits indicate the physical address of Buffer 1. There is no
limitation on the buffer address alignment. See Host data buffer alignment for further details on
buffer address alignment.
TTSL: Before it clears the OWN bit in TDES0, the DMA updates this field with the 32 least
significant bits of the time stamp captured for the corresponding transmit frame (overwriting
the value for TBAP1). This field has the time stamp only if time stamping is activated for this
frame (see TTSE, TDES0 bit 25) and if the Last segment control bit (LS) in the descriptor is
set.
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
TBAP2/TBAP2/TTSH
rw
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