RELEASED
PM7380 FREEDM-32P672
DATA SHEET
PMC-1990262
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 32P672
complete. This action will result in any write data being lost and any read data
being erroneous.
9.6.2 Master Local Bus Interface
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 RMAC672 and the other the TMAC672. Each local master
interface has been optimised to support the traffic pattern generated by the
RMAC672 or the TMAC672 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 RMAC672 and TMAC672 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 RMAC672 provides for byte addressability of write
transactions whereas the interface for the TMAC672 provides for byte
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
60
PMC [ PMC-SIERRA, INC ]
