UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
711 of 1269
NXP Semiconductors
UM10503
Chapter 26: LPC43xx Ethernet
Table 567. DMA operation mode register (DMA_OP_MODE, address 0x4001 1018) bit description
Bit
Symbol
Description
Reset
value
Access
0
-
Reserved
0
RO
1
SR
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.
0
R/W
2
OSF
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.
0
R/W
4:3
RTC
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
0
R/W
5
-
Reserved
0
RO
6
FUF
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).
0
R/W
7
FEF
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.
0
R/W
12:8
-
Reserved
0
RO