2. PCI Interface
71
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
2.6.6.2
Host Free List Address
The address and size of the Host Free List FIFO is provided to the IOP by the I
2
O System Host in an
I
2
O defined “IOP Message Pull Extensions” Message. The Host Free List FIFO structure is located at a
memory boundary equal to its size to enable the IOP to know when it has reached the end of the FIFO.
When the IOP returns XMFAs to the Host Free List FIFO sets the P bit to 1. When the IOP reaches the
end of the FIFO resets the FIFO index to the base address and this time through write the P bit to 0.
This allows the Host to track the progress of the local IOP in returning XMFAs.
illustrates the following steps in PowerSpan II I
2
0 pull capability:
1.
Host reads XMFA from Host Free List
2.
Host writes message to MF in Host memory
3.
Host writes XMFA to Inbound Queue
4.
Local processor reads XMFA from the Inbound Post List FIFO
5.
Local processor copies MF from Host memory
6.
Local processor writes XMFA to Host Free List Index