NXP Semiconductors /LPC43xx /ETHERNET /DMA_BUS_MODE

Software reset This register field can be read by the application (Read), can be set to 1 by the application with a register write of 1 (Write Set), and is cleared to 0 by the Ethernet core (Self Clear). The application cannot clear this type of field, and a register write of 0 to this bit has no effect on this field. 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. The reset operation is completed only when all the resets in all the active clock domains are de-asserted. Hence it is essential that all the PHY inputs clocks (applicable for the selected PHY interface) are present for software reset completion.

DMA arbitration scheme 0 = Round-robin with Rx:Tx priority given in bits [15:14] 1 = Rx has priority over Tx

Descriptor skip length This bit specifies the number of Word 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, then the descriptor table is taken as contiguous by the DMA, in Ring mode.

Alternate descriptor size When set, the alternate descriptor (see Section 26.7.6.3) size is increased to 32 bytes (8 DWORDS). This is required when the Advanced Time-Stamp feature or Full IPC Offload Engine is enabled in the receiver. When reset, the descriptor size reverts back to 4 DWORDs (16 bytes).

Programmable burst length These bits indicate the maximum number of beats to be transferred in one DMA transaction. This will be the maximum value that is used in a single block Read/Write. The DMA will always attempt 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 will result in undefined behavior. When USP is set high, 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 in the MTL layer and the data bus width on the DMA. The FIFO has a constraint that the maximum beat supported is half the depth of the FIFO, except when specified (as given below). For different data bus widths and FIFO sizes, the valid PBL range (including x8 mode) is provided in the following table. 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.

Rx-to-Tx priority ratio RxDMA requests given priority over TxDMA requests in the following ratio. This is valid only when the DA bit is reset. 00 = 1-to-1 01 = 2-to-1 10 = 3-to-1 11 = 4-to-1

Fixed burst This bit controls whether the AHB Master interface performs fixed burst transfers or not. When set, the AHB will use only SINGLE, INCR4, INCR8 or INCR16 during start of normal burst transfers. When reset, the AHB will use SINGLE and INCR burst transfer operations.

RxDMA PBL These bits indicate the maximum number of beats to be transferred in one RxDMA transaction. This will be the maximum value that is used in a single block Read/Write. The RxDMA will always attempt to burst as specified in RPBL each time it starts a Burst transfer on the host bus. RPBL can be programmed with permissible values of 1, 2, 4, 8, 16, and 32. Any other value will result in undefined behavior. These bits are valid and applicable only when USP is set high.

Use separate PBL When set high, it configures the RxDMA to use the value configured in bits [22:17] as PBL while the PBL value in bits [13:8] is applicable to TxDMA operations only. When reset to low, the PBL value in bits [13:8] is applicable for both DMA engines.

8 x PBL mode When set high, this bit multiplies the PBL value programmed (bits [22:17] and bits [13:8]) eight times. Thus the DMA will transfer data in to a maximum of 8, 16, 32, 64, 128, and 256 beats depending on the PBL value. This bit function is not backward compatible. Before version 3.50a, this bit was 4xPBL.

Address-aligned beats When this bit is set high and the FB bit equals 1, the AHB interface generates all bursts aligned to the start address LS bits. If the FB bit equals 0, the first burst (accessing the data buffer’s start address) is not aligned, but subsequent bursts are aligned to the address.

Mixed burst When this bit is set high and FB bit is low, the AHB master interface will start all bursts of length more than 16 with INCR (undefined burst) whereas it will revert to fixed burst transfers (INCRx and SINGLE) for burst-length of 16 and below.

When set, this bit indicates that the transmit DMA has higher priority than the receive DMA during arbitration for the system-side bus.

Reserved