Control of PCI memory read behavior using memory read alias and memory command reissue bits
View Patent ↗A method of controlling memory read behavior in PCI devices includes connecting a master PCI device to a PCI bus. The master PCI device is constructed and arranged to issue a Memory Read Line or a Memory Read Multiple initial command. A target PCI bridge device is connected to the PCI bus. The target PCI bridge device is constructed and arranged to prefetch data from host memory on behalf of the master PCI device and to store the prefetched data. A data transfer transaction is established between the master PCI device and the target PCI bridge device and prefetched data is stored at the target PCI bridge device. A bit is selectively preset in at least one of the PCI devices such that if a disconnect of the transaction occurs, the target PCI bridge device recognizes a subsequent request as a continuation of the initial request and sends prefetched data to the master PCI device.
1. A method of controlling memory read behavior in PCI devices, the method including:
connecting a master PCI device to a PCI bus, the master PCI device being constructed and arranged to issue a memory read command as one of a Memory Read Line or Memory Read Multiple initial command,
connecting a target PCI bridge device to the PCI bus, the target PCI bridge device being constructed and arranged to prefetch data on behalf of the master PCI device from host memory and to store the prefetched data,
establishing a data transfer transaction between the master PCI device and the target PCI bridge device,
storing prefetched data at the target PCI bridge device, and
if a disconnect of the transaction occurs, ignoring changes in the memory read command so that the target PCI bridge device recognizes a subsequent request as a continuation of the initial request and sends prefetched data to the master PCI device.
2. The method of claim 1 , wherein the prefetched data is stored in buffer of the PCI bridge device.
3. The method of claim 1 , wherein the step of ignoring includes setting a Memory Command Reissue bit in the master PCI device to 1.
4. The method of claim 1 , wherein the step of ignoring includes setting a Memory Read Alias Enable bit in the target PCI bridge device to 1 and the method further includes ignoring a REQ64# signal at the target PCI bridge device.
5. A method of controlling memory read behavior in a PCI device, the method including:
connecting a master PCI device to a PCI bus, the master PCI device being constructed and arranged to issue a memory read command as one of a Memory Read Line, or Memory Read Multiple command to target PCI device connected to the PCI bus,
establishing a data transfer transaction between the master PCI device and the target PCI device,
if a disconnect of the transaction occurs, ignoring changes in the memory read command and reissuing said command by the master PCI device upon reconnect regardless of how much more data the master PCI device wants to receive, which enables the target PCI device to recognize the command as a continuation of the original transaction.
6. The method of claim 5 , wherein the step of ignoring includes setting a Memory Command Reissue bit in the master PCI device to 1.
7. A method of controlling memory read behavior in a PCI device, the method including:
connecting a master PCI device to a PCI bus, the master PCI device being constructed and arranged to issue a memory read command as one of a Memory Read Line or Memory Read Multiple initial command to a target PCI bridge device connected to the PCI bus, the target PCI bridge device being constructed and arranged to prefetch data from host memory on behalf of the master PCI device and to store the prefetched data,
establishing a data transfer transaction between the master PCI device and the target PCI bridge device,
storing prefetched data at the target PCI bridge device, and
if a disconnect of the transaction occurs, ignoring changes in the memory read command so that the target PCI bridge device recognizes a subsequent command as a continuation of the initial command and sends prefetched data to the master PCI device.
8. The method of claim 7 , wherein the prefetched data is stored in buffer of the target PCI bridge device.
9. The method of claim 8 , wherein the step of ignoring includes setting a Memory Read Alias Enable bit in the target PCI bridge device to 1 and the method further includes ignoring a REQ64# signal at the target PCI bridge device.
10. A target PCI bridge device comprising:
a prefetch data buffer constructed and arranged to store prefetched data on behalf of a master PCI device, and
means for ignoring changes in a memory read command such that if a disconnect of a transaction between the target PCI bridge device and the master PCI device occurs, the target PCI bridge device recognizes a subsequent read command as a continuation of a previously received read command and sends prefetched data to the master PCI device.
11. The device of claim 10 , wherein the means for ignoring is a Memory Read Alias Enable bit set to 1.
12. A master PCI device comprising:
a command structure constructed and arranged to send a memory read command as one of a Memory Read Line or a Memory Read Multiple command to a target PCI device, and
means for ignoring changes in the memory read command such that if a disconnect of a transaction between the target PCI device and the master PCI device occurs, the master PCI device reissues said command upon reconnection with the target PCI device regardless of how much data the master PCI device wants to receive.
13. The device of claim 12 , wherein the means for ignoring is a Memory Command Reissue bit set to 1.