SECTION 3
PCI 9080
FUNCTIONAL DESCRIPTION
PLX Technology, Inc., 1997
Page 29
Version 1.02
The local processor or PCI requires DMA. PCI 9080 is
master on both the PCI and local buses. Direct Slave or
Direct Master pre-empts DMA.
PCI 9080 releases the PCI bus if one of the following
occurs (refer to Figure 3-15):
FIFO full
Terminal count reached
PCI Latency Timer (PCI:0Dh)(LOC:0Dh) expires
(refer to Table 4-16[7:0])—normally programmed by
the Host PCI BIOS— and PCI GNT# de-asserts
PCI host asserts STOP
Direct Master request pending
*
*
!
"#
$
% &
Figure 3-15. DMA, PCI to Local
PCI 9080 releases the local bus if one of the following
occurs (refer to Figure 3-16):
FIFO empty
Terminal count reached
Local Bus Latency Timer (PCI:08h or PCI:ACh)
(LOC:88h or LOC:12Ch) expires (refer to
Table 4-35[7:0])
BREQ# input asserted
Direct Slave request pending
!
"#
$
'
*
*
Figure 3-16. DMA, Local to PCI
3.7.2 Chaining Mode DMA
In Chaining mode DMA, the Host Processor or the Local
Processor sets up descriptor blocks in local or host
memory that are composed of a PCI address, local
address, transfer count, transfer direction, and address
of the next descriptor block (refer to Figure 3-18). Host
or Local Processor then sets up the address of the initial
descriptor block in the descriptor pointer register of the
PCI 9080 and initiates the transfer by setting a control
bit. PCI 9080 loads the first descriptor block and initiates
the data transfer. PCI 9080 continues to load descriptor
blocks and transfer data until it detects the end of chain
bit is set in the next descriptor pointer register. PCI 9080
can be programmed to interrupt the local processor by
setting the "Interrupt after Terminal Count" bit or PCI
host upon completion of each block transfer and after all
block transfers are complete (done) (refer to Figure
3-17). If chaining descriptors are located in local
memory, the DMA controller can be programmed to
clear the transfer size at the completion of each DMA.
(Refer to DMA Clear Count mode, Table 4-62[16] and
Table 4-67[16].)
Notes:
In Chaining mode DMA, the descriptor includes
PCI address, local address, transfer size and the next
descriptor pointer. (PCI:84h, location 104-PCI:90h,
location 110D). The descriptor pointer register contains
the end of chain bit, direction of transfer, next descriptor
address, and next descriptor location.
DMA descriptor can be on the local memory or PCI
memory, or both (first descriptor on local memory, and
second descriptor on PCI memory).