RM0033 Rev 9 947/1381
RM0033 Ethernet (ETH): media access control (MAC) with DMA controller
956
Bit 25 RSF: Receive store and forward
When this bit is set, a frame is read from the Rx FIFO after the complete frame has been
written to it, ignoring RTC bits. When this bit is cleared, the Rx FIFO operates in Cut-through
mode, subject to the threshold specified by the RTC bits.
Bit 24 DFRF: 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 cleared (see Receive process
suspended).
Bits 23:22 Reserved, must be kept at reset value.
Bit 21 TSF: Transmit store and forward
When this bit is set, transmission starts when a full frame resides in the Transmit FIFO.
When this bit is set, the TTC values specified by the ETH_DMAOMR register bits [16:14] are
ignored.
When this bit is cleared, the TTC values specified by the ETH_DMAOMR register bits
[16:14] are taken into account.
This bit should be changed only when transmission is stopped.
Bit 20 FTF: Flush transmit FIFO
When this bit is set, the transmit FIFO controller logic is reset to its default values and thus
all data in the Tx FIFO are lost/flushed. This bit is cleared internally when the flushing
operation is complete. The Operation mode register should not be written to until this bit is
cleared.
Bits 19:17 Reserved, must be kept at reset value.
Bits 16:14 TTC: Transmit threshold control
These three bits control the threshold level of the Transmit FIFO. Transmission starts when
the frame size within the 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 cleared.
000: 64
001: 128
010: 192
011: 256
100: 40
101: 32
110: 24
111: 16
Bit 13 ST: Start/stop transmission
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 ETH_DMATDLAR 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 the transmit buffer unavailable bit (ETH_DMASR [2]) is set. The
Start Transmission command is effective only when transmission is stopped. If the command
is issued before setting the DMA ETH_DMATDLAR register, the DMA behavior is
unpredictable.
When this bit is cleared, 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 when the transmission of the current frame is
complete or when the transmission is in the Suspended state.
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