NXP Semiconductors LPC24XX UM10237 - Manual (Page 260)

UM10237_4 © NXP B.V. 2009. All rights reserved.
User manual Rev. 04 — 26 August 2009 260 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
addresses of a packet are calculated once for all the fragments belonging to the same
packet and then stored in every StatusHashCRC word of the statuses associated with the
corresponding fragments. If the reception reports an error, any remaining data in the
receive frame is discarded and the LastFrag bit will be set in the receive status field, so
the error flags in all but the last fragment of a frame will always be 0.
The status of the last received frame can also be inspected by reading the RSV register.
The register does not report statuses on a fragment basis and does not store information
of previously received frames. RSV is provided primarily for debug purposes, because the
communication between driver software and the Ethernet block takes place through the
frame descriptors.
Reception error handling
When an error occurs during the receive process, the Rx DMA manager will report the
error via the receive StatusInfo written in the Status array and the IntStatus interrupt status
register.
The receive process can generate several types of errors: AlignmentError, RangeError,
LengthError, SymbolError, CRCError, Overrun, and NoDescriptor. All have corresponding
bits in the receive StatusInfo. In addition to the separate bits in the StatusInfo,
AlignmentError, RangeError, LengthError, SymbolError, and CRCError are ORed together
into the Error bit of the StatusInfo. Errors are also propagated to the IntStatus register; the
RxError bit in the IntStatus register is set if there is an AlignmentError, RangeError,
LengthError, SymbolError, CRCError, or NoDescriptor error; nonfatal overrun errors are
reported in the RxError bit of the IntStatus register; fatal Overrun errors are report in the
RxOverrun bit of the IntStatus register. On fatal overrun errors, the Rx datapath needs to
be soft reset by setting the RxReset bit in the Command register.
Overrun errors can have three causes:
• In the case of a multi-fragment reception, the next descriptor may be missing. In this
case the NoDescriptor field is set in the status word of the previous descriptor and the
RxError in the IntStatus register is set. This error is nonfatal.
• The data flow on the receiver data interface stalls, corrupting the packet. In this case
the overrun bit in the status word is set and the RxError bit in the IntStatus register is
set. This error is nonfatal.
• The flow of reception statuses stalls and a new status has to be written while a
previous status still waits to be transferred across the memory interface. This error will
corrupt the hardware state and requires the hardware to be soft reset. The error is
detected and sets the Overrun bit in the IntStatus register.
The first overrun situation will result in an incomplete frame with a NoDescriptor status
and the RxError bit in IntStatus set. Software should discard the partially received frame.
In the second overrun situation the frame data will be corrupt which results in the Overrun
status bit being set in the Status word while the IntError interrupt bit is set. In the third case
receive errors cannot be reported in the receiver Status arrays which corrupts the
hardware state; the errors will still be reported in the IntStatus register’s Overrun bit. The
RxReset bit in the Command register should be used to soft reset the hardware.
Device drivers should catch the above receive errors and take action.
Receive triggers interrupts