NXP Semiconductors /LPC43xx /ETHERNET /DMA_OP_MODE

Reserved

Start/stop receive When this bit is set, the Receive process is placed in the Running state. The DMA attempts to acquire the descriptor from the Receive list and processes incoming frames. Descriptor acquisition is attempted from the current position in the list, which is the address set by the DMA_REC_DES_ADDR register or the position retained when the Receive process was previously stopped. If no descriptor is owned by the DMA, reception is suspended and Receive Buffer Unavailable bit (bit 7 in DMA_STAT register) is set. The Start Receive command is effective only when reception has stopped. If the command was issued before setting the DMA_REC_DES_ADDR, DMA behavior is unpredictable.

Operate on second frame When this bit is set, this bit instructs the DMA to process a second frame of Transmit data even before status for first frame is obtained.

Receive threshold control These two bits control the threshold level of the MTL Receive FIFO. Transfer (request) to DMA starts when the frame size within the MTL Receive FIFO is larger than the threshold. In addition, full frames with a length less than the threshold are transferred automatically. These bits are valid only when the RSF bit is zero, and are ignored when the RSF bit is set to 1. 00 = 64 01 = 32 10 = 96 11 = 128

Reserved

Forward undersized good frames When set, the Rx FIFO will forward Undersized frames (frames with no Error and length less than 64 bytes) including pad-bytes and CRC). When reset, the Rx FIFO will drop all frames of less than 64 bytes, unless it is already transferred due to lower value of Receive Threshold (e.g., RTC = 01).

Forward error frames When this bit is reset, the Rx FIFO drops frames with error status (CRC error, collision error, , watchdog timeout, overflow). However, if the frame’s start byte (write) pointer is already transferred to the read controller side (in Threshold mode), then the frames are not dropped. When FEF is set, all frames except runt error frames are forwarded to the DMA. But when RxFIFO overflows when a partial frame is written, then such frames are dropped even when FEF is set.

Reserved

Start/Stop Transmission Command When this bit is set, transmission is placed in the Running state, and the DMA checks the Transmit List at the current position for a frame to be transmitted. Descriptor acquisition is attempted either from the current position in the list, which is the Transmit List Base Address set by the DMA_TRANS_DES_ADDR register or from the position retained when transmission was stopped previously. If the current descriptor is not owned by the DMA, transmission enters the Suspended state and Transmit Buffer Unavailable (DMA_STAT register, bit 2) is set. The Start Transmission command is effective only when transmission is stopped. If the command is issued before setting the DMA_TRANS_DES_ADDR register, then the DMA behavior is unpredictable. When this bit is reset, the transmission process is placed in the Stopped state after completing the transmission of the current frame. The Next Descriptor position in the Transmit List is saved, and becomes the current position when transmission is restarted. The stop transmission command is effective only the transmission of the current frame is complete or when the transmission is in the Suspended state.

Transmit threshold control These three bits control the threshold level of the MTL Transmit FIFO. Transmission starts when the frame size within the MTL Transmit FIFO is larger than the threshold. In addition, full frames with a length less than the threshold are also transmitted. These bits are used only when the TSF bit (Bit 21) is reset. 000 = 64 001 = 128 010 = 192 011 = 256 100 = 40 101 = 32 110 = 24 111 = 16

Reserved

Flush transmit FIFO 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 transmit FIFO controller logic is reset to its default values and thus all data in the Tx FIFO is lost/flushed. This bit is cleared internally when the flushing operation is completed fully. The Operation Mode register should not be written to until this bit is cleared. The data which is already accepted by the MAC transmitter will not be flushed. It will be scheduled for transmission and will result in underflow and runt frame transmission. The flush operation completes only after emptying the TxFIFO of its contents and all the pending Transmit Status of the transmitted frames are accepted by the host. In order to complete this flush operation, the PHY transmit clock is required to be active.

Reserved

Reserved

Disable flushing of received frames When this bit is set, the RxDMA does not flush any frames due to the unavailability of receive descriptors/buffers as it does normally when this bit is reset. (See).

Reserved

Reserved

Reserved