Altera PCI Compiler - Manual (Page 153)

Altera Corporation User Guide Version 11.1 3–79
October 2011
Functional Description
Disconnect
A PCI target can signal a disconnect by asserting stopn and devseln
after at least one data phase is complete. There are two types of
disconnects: disconnect with data and disconnect without data. In a
disconnect with data, trdyn is asserted while stopn is asserted.
Therefore, one more data phases is completed while the PCI bus master
finishes the transaction. A disconnect without data occurs when the
target device deasserts trdyn while stopn is asserted, thus ensuring that
no more data phases are completed in the transaction. Depending on the
sequence of the lt_rdyn and 1t_discn signals’ assertion on the local
side and the irdyn signal’s assertion on the PCI side, the PCI MegaCore
function issues either a disconnect with data or disconnect without data
.
Since disconnect with data or disconnect without data transactions
depend upon the sate of the irdyn signal, you must design your logic to
disconnect after the specified number of DWORDs are transferred on the
PCI bus. You can use lt_ackn and lt_dxfrn to check the number of
DWORD
s transferred on the local side and use lt_tsr[10] to check the
number of DWORDs transferred on the PCI bus.
1 The PCI Local Bus Specification, Revision 3.0 requires that a target
device issues a disconnect if a burst transaction goes beyond its
address range. In this case, the local-side device must request a
disconnect. The local-side device must keep track of the current
data transfer address; if the transfer exceeds its address range,
the local side should request a disconnect by asserting
lt_discn
.