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PEB 20321
PEF 20321
Local Bus Interface (LBI)
Data Sheet
147
2001-02-14
bit field of Mailbox Command Register, which causes an interrupt to be generated to the
PCI host system, informing the PCI host system that the data transfer is complete.
The PCI host system completes its participation of the transaction by reading the Status
Register STAT (to determine the cause of the interrupt), writing a
‘
1
’
to the Status
Acknowledge Register
’
s MBI bit field to deassert the PCI INTA signal.
Alternately
, consider when the intelligent LBI peripheral wants to transfer data to the
PCI host system. First, assuming it has
‘
ownership
’
of the Mailbox registers, it loads data
into the Mailbox Data Registers, and then writes a
‘
1
’
to the INLBI bit field of Mailbox
Command Register. This causes an interrupt to be generated to the PCI host system,
indicating to the PCI host system that data is ready.
The PCI host system reads the Status Register STAT (to determine the cause of the
interrupt), writes a
‘
1
’
to the Status Acknowledge Register
’
s MBI bit field to deassert the
PCI INTA signal, and then reads the data from the Mailbox Data Registers. Next, it writes
a
‘
1
’
to the INPCI bit field of the Mailbox Command Register, which asserts the LINTO
signal to the LBI peripheral.
The intelligent LBI peripheral completes its participation of the transaction when it reads
Mailbox Command Register, which deasserts the LINTO signal and resets the INLBI bit
field of the Mailbox Command Register.
6.1.3
The architecture of the Mailbox registers requires the PCI host system software to
provide Mailbox arbitration. The primary data transfer control requirement is that only the
current
‘
owner
’
of the Mailbox registers may write data into the Mailbox Data Registers.
Typically, upon exiting reset, the PCI host system becomes the Mailbox
‘
owner
’
and may
transfer data to the LBI. If the LBI desires to transfer data to the PCI host system, it must
generate an interrupt to the PCI host system (by writing a
‘
1
’
to INLBI bit field in Mailbox
Command Register MBCMD), informing the PCI host system that it requests
‘
ownership
’
of the Mailbox registers. It is the responsibility of the PCI host system software arbiter to
handle the request/grant protocol.
Software Arbiter/Data Transfer Control
6.1.4
The organization of the Mailbox registers is partioned into an
‘
exclusive-access
’
Mailbox
Command Register, and into seven Mailbox Data Registers, as shown below.
Mailbox Registers