NXP Semiconductors LPC24XX UM10237 - Manual (Page 261)

UM10237_4 © NXP B.V. 2009. All rights reserved.
User manual Rev. 04 — 26 August 2009 261 of 792
NXP Semiconductors
UM10237
Chapter 11: LPC24XX Ethernet
The receive datapath can generate four different interrupt types:
• If the Interrupt bit in the descriptor Control field is set, the Rx DMA will set the
RxDoneInt bit in the IntStatus register after receiving a fragment and committing the
associated data and status to memory. Even if a descriptor (fragment) is not the last in
a multi-fragment frame, the Interrupt bit in the descriptor can be used to generate an
interrupt.
• If the descriptor array is full while the Ethernet hardware is enabled, the hardware will
set the RxFinishedInt bit of the IntStatus register.
• If the AHB interface does not consume receive statuses at a sufficiently high
bandwidth, the receive status process may overrun, in which case the RxOverrun bit
will be set in the IntStatus register.
• If there is a receive error (AlignmentError, RangeError, LengthError, SymbolError, or
CRCError), or a multi-fragment frame where the device driver did provide descriptors
for the initial fragments but did not provide the descriptors for the rest of the
fragments, or if a nonfatal data Overrun occurred, the hardware will set the RxErrorInt
bit of the IntStatus register.
All of the above interrupts can be enabled and disabled by setting or resetting the
corresponding bits in the IntEnable register. Enabling or disabling does not affect the
IntStatus register contents, only the propagation of the interrupt status to the CPU (via the
Vectored Interrupt Controller).
The interrupts, either of individual frames or of the whole list, are a good means of
communication between the DMA manager and the device driver, triggering the device
driver to inspect the status words of descriptors that have been processed.
Device driver processes receive data
As a response to status (e.g. RxDoneInt) interrupts or polling of the RxProduceIndex, the
device driver can read the descriptors that have been handed over to it by the hardware
(RxProduceIndex - RxConsumeIndex). The device driver should inspect the status words
in the status array to check for multi-fragment receptions and receive errors.
The device driver can forward receive data and status to upper software layers. After
processing of data and status, the descriptors, statuses and data buffers may be recycled
and handed back to hardware by incrementing the RxConsumeIndex.
Receive example
Figure 11–31 illustrates the receive process in an example receiving a frame of 19 bytes.