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"Frame data is transferred to and from the EMAC through the DMA interface. All transfers are 32-bit
words and may be single accesses or bursts of 2, 3 or 4 words. Burst accesses do not cross
sixteen-byte boundaries. Bursts of 4 words are the default data transfer; single accesses or
bursts of less than four words may be used to transfer data at the beginning or the end of a
buffer."
"Receive Buffers
Received frames, including CRC/FCS optionally, are written to receive buffers stored in mem-ory.
Each receive buffer is 128 bytes long. The start location for each receive buffer is stored in
memory in a list of receive buffer descriptors at a location pointed to by the receive buffer queue
pointer register. The receive buffer start location is a word address. For the first buffer of a
frame, the start location can be offset by up to three bytes depending on the value written to bits
14 and 15 of the network configuration register. If the start location of the buffer is offset the
"To receive frames, the buffer descriptors must be initialized by writing an appropriate address to
bits 31 to 2 in the first word of each list entry. Bit zero must be written with zero. Bit one is the
wrap bit and indicates the last entry in the list.
The start location of the receive buffer descriptor list must be written to the receive buffer queue
pointer register before setting the receive enable bit in the network control register to enable
receive. As soon as the receive block starts writing received frame data to the receive FIFO, the
receive buffer manager reads the first receive buffer location pointed to by the receive buffer
queue pointer register.
If the filter block then indicates that the frame should be copied to memory, the receive data
DMA operation starts writing data into the receive buffer. If an error occurs, the buffer is recov-ered.
If the current buffer pointer has its wrap bit set or is the 1024 th descriptor, the next receive
buffer location is read from the beginning of the receive descriptor list. Otherwise, the next
receive buffer location is read from the next word in memory."
Я так понял что умный
available length of the first buffer of a frame is reduced by the corresponding number of bytes."
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