DocID13902 Rev 15 1012/1128
RM0008 Ethernet (ETH): media access control (MAC) with DMA controller
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• 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.
29.6.8 Rx DMA configuration
The Receive DMA engine’s reception sequence is illustrated in Figure 356 and described
below:
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 on page 1002 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
Bits 31:0 TBAP2: Transmit buffer 2 address pointer (Next descriptor address) / Transmit frame time
stamp high
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.
TBAP2: When the software makes this descriptor available to the DMA (at the moment when
the OWN bit is set to 1 in TDES0), these bits indicate the physical address of Buffer 2 when a
descriptor ring structure is used. If the Second address chained (TDES1 [20]) bit is set, this
address contains the pointer to the physical memory where the next descriptor is present. The
buffer address pointer must be aligned to the bus width only when TDES1 [20] is set. (LSBs are
ignored internally.)
TTSH: Before it clears the OWN bit in TDES0, the DMA updates this field with the 32 most
significant bits of the time stamp captured for the corresponding transmit frame (overwriting
the value for TBAP2). This field has the time stamp only if time stamping is activated for this
frame (see TDES0 bit 25, TTSE) and if the Last segment control bit (LS) in the descriptor is
set.
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