28
Specification Update
Intel
®
80219 General Purpose PCI Processor
Specification Clarifications
6.
In-order Delivery not guaranteed for data blocks described by a single DMA
descriptor
Issue:
In-order delivery is not guaranteed for data blocks described by a single DMA descriptor that
crosses a 1 KB boundary. This may result in out of order execution of the DMA transfer. When
multiple DMA descriptors are used the ordering is maintained with respect to the blocks described
by each descriptor. When ordering is important, the ordering needs to be maintained by splitting
the relevant pieces of data into multiple DMA descriptors.
Example
A 100 byte DMA transfer described by a single descriptor with a source address of
0x3ff8. Since each DMA channel has two 1 KB buffers, the DMA unit breaks this
transaction at the 1 KB boundary. Therefore, the first buffer might fetch the 8 bytes
from 0x3ff8-0x3fff and the second buffer might fetch the remaining 92 byes from
0x4000-0x405C. Both buffers have the ability to access the internal bus, without
preference (i.e., either buffer may gain access first). Therefore, it is possible the
92 bytes of data after the 1 KB boundary could be transferred to the destination
before the first 8 bytes. However, the transaction is completed and all data has been
copied to the correct address when the descriptor completes (i.e., descriptors are
not completed out of order).
Status:
When a data delivery sequence is required, descriptors should be used to ensure sequenced arrival
(e.g., in the example above), break the data into blocks then use multiple descriptors linked in the
correct order to ensure sequential data delivery.
7.
Writing to reserved registers can cause unexpected behavior
Issue:
The Intel
®
80219 General Purpose PCI Processor contains several reserved registers. The
Intel
®
80219 General Purpose PCI Processor Developer’s Manual
(Section 15.5 Table 273) states that
memory map register locations FFFFE800H - FFFFE8FFH are reserved. Writing to these can cause
the processor to enter an undesired state.
Status:
NoFix
.
