User guide

116 DC 900-1338I
Protocol Software Toolkit Programmer Guide
to the ICP in order to gain service. Another register is used for ICP-to-host commands,
but another device’s registers must be set up to generate the interrupt to the host.
ICP2424s use a region of shared memory to support the PXR. The ICP2424 PXR is the
first 16 bytes of the shared memory. These are consecutive bytes addressable as bytes,
words, or longwords as long as the proper boundaries are observed.
The PXR for the ICP2432 is implemented via mailboxes within the PCI interface chip.
They are accessed as 32-bit entities.
The host driver and the ICP driver have a master/slave relationship. The master is the
driver that actually moves the data between the host and the ICP. For the ICP2432 and
ICP6000, the ICP is the master. For the ICP2424, the host is the master.
When the slave has a buffer into which data may be transferred, it issues a “read”
request to the master along with the address of the buffer and the maximum amount of
data it can hold. When the master receives a matching request from its application pro-
gram and moves the data into the buffer, it signals the slave that the “read” is complete.
When the slave has a buffer of data ready to transfer to the master, it issues a “write”
request to the master with the address of the data’s buffer and the amount of data in it.
When the master receives a matching request from its application program, it transfers
the data and signals the slave with a “write” complete.
As the protocol is asynchronous, the slave can send any number of requests to the mas-
ter without waiting for completions on previous requests, and the master can process
requests and return completions in any order.
The ICP driver and the host driver coordinate the information flowing between the ICP
and the host processor by means of node numbers. Each node can have one read and
one write queue. At startup, the utility task creates the nodes it will be using, up to the
maximum number of nodes allowed by the configuration parameters of the two driv-
ers.