Texas Instruments TMS320TCI6486 - Manual (Page 60)

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2.11.6 Receive Channel Teardown
The host commands a receive channel teardown by writing the channel number to the RXTEARDOWN
register. When a teardown command is issued to an enabled receive channel, the following occurs:
• Any current frame in reception completes normally.
• The TDOWNCMPLT flag is set in the next buffer descriptor in the chain, if there is one.
• The channel head descriptor pointer is cleared.
• A receive interrupt for the channel is issued to the host.
• The corresponding RXnCP register contains the value FFFF FFFCh.
• The host should acknowledge a teardown interrupt with an FFFF FFFCh acknowledge value.
Channel teardown may be commanded on any channel at any time. The host is informed of the teardown
completion by the set teardown complete buffer descriptor bit. The EMAC does not clear any channel
enables due to a teardown command. A teardown command to an inactive channel issues an interrupt
that software should acknowledge with an FFFF FFFCh acknowledge value to RXnCP (note that there is
no buffer descriptor in this case). Software may read RXnCP to determine if the interrupt was due to a
commanded teardown. The read value is FFFF FFFCh if the interrupt was due to a teardown command.
2.11.7 Receive Frame Classification
Received frames are proper, or good, frames if they are between 64 and RXMAXLEN in length (inclusive)
and contain no code, align, or CRC errors.
Received frames are long frames if their frame count exceeds the value in the RXMAXLEN register. The
RXMAXLEN register default reset value is 5EEh (1518 in decimal). Long received frames are either
oversized or jabber frames. Long frames with no errors are oversized frames; long frames with CRC,
code, or alignment errors are jabber frames.
Received frames are short frames if their frame count is less than 64 bytes. Short frames that address
match and contain no errors are undersized frames; short frames with CRC, code, or alignment errors are
fragment frames. If the frame length is less than or equal to 20, then the frame CRC is passed, regardless
of whether the RXPASSCRC bit is set or cleared in the RXMBPENABLE register.
A received long packet always contains RXMAXLEN number of bytes transferred to memory (if the
RXCEFEN bit is set in RXMBPENABLE) regardless of the value of the RXPASSCRC bit. Following is an
example with RXMAXLEN set to 1518:
• If the frame length is 1518, then the packet is not a long packet and there are 1514 or 1518 bytes
transferred to memory depending on the value of the RXPASSCRC bit.
• If the frame length is 1519, there are 1518 bytes transferred to memory regardless of the
RXPASSCRC bit value. The last three bytes are the first three CRC bytes.
• If the frame length is 1520, there are 1518 bytes transferred to memory regardless of the
RXPASSCRC bit value. The last two bytes are the first two CRC bytes.
• If the frame length is 1521, there are 1518 bytes transferred to memory regardless of the
RXPASSCRC bit value. The last byte is the first CRC byte.
• If the frame length is 1522, there are 1518 bytes transferred to memory. The last byte is the last data
byte.
60 C6472/TCI6486 EMAC/MDIO SPRUEF8F – March 2006 – Revised November 2010
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