RELEASED
PM7380 FREEDM-32P672
DATA SHEET
PMC-1990262
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 32P672
9.6.4 CBI Bus Interface
The CBI bus interface provides access to the CBI address space of the
FREEDM-32P672 blocks. The CBI address space is set by the associated BAR
in the PCI Configuration registers.
Write transfers to the CBI space always write all 32 bits provided that at least
one byte enable is asserted. A write command with all byte enables negated will
be ignored. Read transfers always return the 32 bits regardless of the status of
the byte enables, as long as at least one byte enable is asserted. A read
command with all byte enables negated will be ignored.
9.6.5 Error / Bus Control
The Error/Bus Control block monitors signals from both the Target block and
Master Block to determine the direction of the PCI bus pads and to generate or
check parity. After reset, the GPIC sets all bi-directional PCI bus pads to inputs
and monitors the bus for accesses. The Error/Bus control unit remains in this
state unless either the Master requests the PCI bus or the Target responds to a
PCI Master Access. The Error/Bus control unit decodes the state of each state
machine to determine the direction of each PCI bus signal.
All PCI bus devices are required to check and generate even parity across
AD[31:0] and C/BEB[3:0] signals. The GPIC generates parity on Master address
and write data phases; the target generates parity on read data phases. The
GPIC is required to check parity on all PCI bus phases even if it is not
participating in the cycle. But, the GPIC will report parity errors only if the GPIC
is involved in the PCI cycle or if the GPIC detects an address parity error or data
parity is detected in a PCI special cycle. The GPIC updates the PCI
Configuration Status register for all detected error conditions.
9.7 Transmit DMA Controller
The Transmit DMA Controller block (TMAC672) is a DMA controller which
retrieves packet data from host computer memory for transmission. The minimum
packet data length is two bytes. The TMAC672 communicates with the host
computer bus through the master interface connected to PCI Controller block
(GPIC) which translates host bus specific signals from the host to the master
interface format. The TMAC672 uses the master interface whenever it wishes to
initiate a host bus read or write; in this case, the TMAC672 is the initiator and the
host memory is the target.
The TMAC672 and the host exchange information using transmit descriptors
(TDs). The descriptor contains the size and location of buffers in host memory
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
63
PMC [ PMC-SIERRA, INC ]
