82801CA Datasheet, PDF (179/521 Pages) Intel Corporation – I/O Controller Hub 3-S (ICH3-S)

Functional Description
5.16.2.2
Processing Transfer Descriptors
The ICH3 executes a TD using the following generalized algorithm. These basic steps are common
across all modes of TDs. Subsequent sections present processing steps unique to each TD mode.
1. ICH3 Fetches TD or QH from the current Link Pointer.
2. If a QH, go to 1 to fetch from the Queue Element Link Pointer. If inactive, go to 12
3. Build Token, actual bits are in TD Token.
4. If (Host-to-Function) then
[PCI Access] issue request for data, (referenced through TD.BufferPointer)
wait for first chunk data arrival
end if
5. [Begin USB Transaction] Issue Token (from token built in 2, above) and begin data transfer.
if (Host-to-Function) then Go to 6
else Go to 7
end if
6. Fetch data from memory (via TD BufferPointer) and transfer over USB until TD Max-Length
bytes have been read and transferred. [Concurrent system memory and USB Accesses]. Go to
8.
7. Wait for data to arrive (from USB). Write incoming bytes into memory beginning at TD
BufferPointer. Internal HC buffer should signal end of data packet. Number of bytes received
must be (TD Max-Length; The length of the memory area referenced by TD BufferPointer
must be (TD Max-Length. [Concurrent system memory and USB Accesses].
8. Issue handshake based on status of data received (Ack or Time-out). Go to 10.
9. Wait for handshake, if required [End of USB Transaction].
10. Update Status [PCI Access] (TD.Status and TD.ActualLength).
If the TD was an isochronous TD, mark the TD inactive. Go to 12.
If not an isochronous TD, and the TD completed successfully, mark the TD inactive. Go to 11.
If not successful, and the error count has not been reached, leave the TD active. If the error
count has been reached, mark the TD inactive. Go to 12.
11. Write the link pointer from the current TD into the element pointer field of the QH structure. If
the Vf bit is set in the TD link pointer, go to 2.
12. Proceed to next entry.
Intel^® 82801CA ICH3-S Datasheet
179