Intel 80219 Specification Update page 28

Intel general purpose pci processor specification update

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Intel

80219 General Purpose PCI Processor

Specification Clarifications

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.

Writing to reserved registers can cause unexpected behavior

Issue:

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.

80219 General Purpose PCI Processor contains several reserved registers. The Intel

Specification Update

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