Ethernet (ETH): media access control (MAC) with DMA controller
RM0090
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DocID018909 Rev 11
Ethernet DMA transmit poll demand register (ETH_DMATPDR)
Address offset: 0x1004
Reset value: 0x0000 0000
This register is used by the application to instruct the DMA to poll the transmit descriptor list.
The transmit poll demand register enables the Transmit DMA to check whether or not the
current descriptor is owned by DMA. The Transmit Poll Demand command is given to wake
up the TxDMA if it is in Suspend mode. The TxDMA can go into Suspend mode due to an
underflow error in a transmitted frame or due to the unavailability of descriptors owned by
Bits 15:14
PM:
Rx Tx priority ratio
RxDMA requests are given priority over TxDMA requests in the following ratio:
00: 1:1
01: 2:1
10: 3:1
11: 4:1
This is valid only when the DA bit is cleared.
Bits 13:8
PBL:
Programmable burst length
These bits indicate the maximum number of beats to be transferred in one DMA transaction.
This is the maximum value that is used in a single block read/write operation. The DMA
always attempts to burst as specified in PBL each time it starts a burst transfer on the host
bus. PBL can be programmed with permissible values of 1, 2, 4, 8, 16, and 32. Any other
value results in undefined behavior. When USP is set, this PBL value is applicable for
TxDMA transactions only.
The PBL values have the following limitations:
– The maximum number of beats (PBL) possible is limited by the size of the Tx FIFO and Rx
FIFO.
– The FIFO has a constraint that the maximum beat supported is half the depth of the FIFO.
– If the PBL is common for both transmit and receive DMA, the minimum Rx FIFO and Tx
FIFO depths must be considered.
– Do not program out-of-range PBL values, because the system may not behave properly.
Bit 7
EDFE:
Enhanced descriptor format enable
When this bit is set, the enhanced descriptor format is enabled and the descriptor size is
increased to 32 bytes (8 DWORDS). This is required when time stamping is activated
(TSE=1, ETH_PTPTSCR bit 0) or if IPv4 checksum offload is activated (IPCO=1,
ETH_MACCR bit 10).
Bits 6:2
DSL:
Descriptor skip length
This bit specifies the number of words to skip between two unchained descriptors. The
address skipping starts from the end of current descriptor to the start of next descriptor.
When DSL value equals zero, the descriptor table is taken as contiguous by the DMA, in
Ring mode.
Bit 1
DA:
DMA Arbitration
0: Round-robin with Rx:Tx priority given in bits [15:14]
1: Rx has priority over Tx
Bit 0
SR:
Software reset
When this bit is set, the MAC DMA controller resets all MAC Subsystem internal registers
and logic. It is cleared automatically after the reset operation has completed in all of the core
clock domains. Read a 0 value in this bit before re-programming any register of the core.