![](http://datasheet.mmic.net.cn/330000/PM7367-PI_datasheet_16444408/PM7367-PI_64.png)
DATA SHEET
PM7367 FREEDM-32P32
ISSUE 2
PMC-1991499
FRAME ENGINE AND DATA LINK MANAGER
8.5.2 Master Local Bus Interface
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE
50
The master local bus is a 32 bit data bus which connects the local master device
to the GPIC. The GPIC contains two local master interface blocks, with one
supporting the RMAC and the other the TMAC. Each local master interface has
been optimised to support the traffic pattern generated by the RMAC or the
TMAC and are not interchangeable.
The data path between the GPIC and local master device provides a mechanism
to segregate the system timing domain of the core from the PCI bus. Transfers
on each of the RMAC and TMAC interfaces are timed to its own system clock.
The DMA controllers isolated from all aspects of the PCI bus protocol, and
instead “sees” a simple synchronous protocol. Read or write cycles on the local
master bus will initiate a request for service to the GPIC which will then transfer
the data via the PCI bus.
The GPIC maximises data throughput between the PCI bus and the local device
by paralleling local bus data transfers with PCI access latency. The GPIC allows
either DMA controller to write data independent of each other and independent of
PCI bus control. The GPIC temporarily buffers the data from each DMA
controller while it is arbitrating for control of the PCI bus. After completion of a
write transfer, the DMA controller is then released to perform other tasks. The
GPIC can buffer only a single transaction from each DMA controller.
Read accesses on the local bus are optimised by allowing the DMA controllers
access to the data from the PCI bus as soon as the first data becomes available.
After the initial synchronisation and PCI bus latency data is transferred at the
slower of PCI bus rate or the core logic SYSCLK rate. Once a read transaction
is started, the DMA controller is held waiting for the ready signal while the GPIC
is arbitrating for the PCI bus.
All data is passed between the GPIC and the DMA controllers in little Endian
format and, in the default mode of operation, the GPIC expects all data on the
PCI bus to also be in little Endian format. The GPIC provides a selection bit in
the internal Control register which allows the Endian format of the PCI bus data
to be changed. If enabled, the GPIC will swizzle all packet data on the PCI bus
(but not descriptor references and the contents of descriptors). The swizzling is
performed according to the “byte address invariance” rule, i.e. the only change
to the data is the mirror-imaging of byte lanes.
The interface for the RMAC provides for byte addressability of write transactions
whereas the interface for the TMAC provides for byte addressability of read
transactions. Other transactions must be dword aligned. For byte-addressable
transactions, the data transferred between the local device and the GPIC need
not be dword aligned with the data as it is presented on the PCI bus. The GPIC