GT-96100A Advanced Communication Controller
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Revision 1.0
11. COMMUNICATION INTERFACE UNIT (CIU)
The GT-96100A’s IDMA, Ethernet ports, and SDMA engines have one common interface with the other units
within the GT-96100A. These other units include the CPU interface unit (Punit), the memory control unit (Dunit),
and the PCI unit (Lunit). The common interface supports a single master, meaning that only one agent can gain
control and access the memory (through the Dunit) or the PCI (through the Lunit) at a time.
In order to support this shared interface, the GT-96100A provides an arbitration mechanism, which arbitrates
between requests generated by the IDMA, SDMA, and Ethernet. The arbitration logic supports multiple priority
levels as well as different weights assigned to each priority level. The priority is programmable per request and
the weights are programmable per priority.
This arbitration mechanism also handles MASTER type requests. MASTER requests originate within the com-
munication unit and are targeted at other units in the GT-96100A. For example, a request generated by one of the
Ethernet units and is targeted at the Dunit (for SDRAM read/write access) is a MASTER request. Similarly, a
request generated by the IDMA and is targeted at the PCI unit is also a MASTER request. The transactions asso-
ciated with MASTER requests are referred to as MASTER transactions.
In addition to handling MASTER type requests and MASTER transactions, the arbiter also handles SLAVE
transactions, which originate from other units within the GT-96100A (e.g. Punit, Lunit) and are targeted at the
communication unit. SLAVE requests are used by the other units to access internal registers within the communi-
cation unit. Arbitration between SLAVE type requests is fixed and gives the highest priority to the Punit (i.e.
requests from CPU).
The MASTER/SLAVE arbiter and the associated logic that handle the MASTER/SLAVE transactions are collec-
tively called the Communication Interface Unit (CIU).
This section provides details about the arbitration scheme as well as high level design aspects of the CIU.