Communicating with the Host • 5-1 •
The H.110 Basic Rate ISDN Board
5.0 Communicating with the Host
This section describes how the host computer communicates with the
Infinity Series H.110 Basic Rate ISDN Board. It includes the definitions
for the H.110 BRI Board commands and responses along with a description
of the mailboxes used for messaging.
The board is controlled by the host computer through a system of four
mailboxes. The messages consist of short NUL-terminated ASCII strings,
which are easy for the host software to compose and parse. The board is
capable of buffering up to eight messages in either direction and can drive
an interrupt line when it has a message for the host. Messages may not
exceed 32 characters.
There are two main mailboxes, one for messages to the board and one for
messages from the board, and two flags associated with them. A 00h in a
flag byte indicates the mailbox is free, a non-zero value indicates that the
mailbox is occupied. The mailboxes and their flags are contained in an 8K
block of dual-ported memory at the following offsets:
receive mailbox 1F80h
transmit mailbox 1FC0h
transmit flag 1FFCh
receive flag 1FFEh
The board's base address is determined by reading PCI Configuration
Space offset 18h. The 32-bit value at this location is the base address for
the dual-ported memory on the board.
To send a message, the message is placed in the mailbox and the flag is set
to 01h. To read a message, the message is removed from the mailbox and
the flag is cleared to 00h. This will clear the interrupt hardware.
To Next Page
Loading...