AT&T ORCA FPGAs

AT&T ORCA FPGAs

AT&T’s are SRAM-based FPGAs.
Its features and overall structure similar to that in Xilinx FPGAs.
It is called Optimized Reconfigurable Cell Array (ORCA).
The ORCA logic block is based on LUTs, containing an array of Programmable Function Units (PFUs).

The structure of a PFU is shown in below Figure .


Figure: AT&T Programmable Function Unit (PFU).

A PFU possesses a unique kind of configurability among LUT-based logic blocks, in that it can be configured in the following ways: as four 4-input LUTs, as two 5-input LUTs, and as one 6-input LUT. A key element of this architecture is that when used as four 4-input LUTs, several of the LUTs’ inputs must come from the same PFU input. While this reduces the apparent functionality of the PFU, it also significantly reduces the cost of the wiring associated with the chip. The PFU also includes arithmetic circuitry, like Xilinx XC4000 and Altera FLEX 8000, and like Xilinx XC4000 a PFU can be configured as a RAM block.

A recently announced version of the ORCA chip also allows dual-port and synchronous RAM.

ORCA’s interconnect structure is also different from those in other SRAM-based FPGAs.

Each PFU connects to interconnect that is configured in four-bit buses. This provides for more
efficient support for “system-level” designs, since buses are common in such applications.
The ORCA family has been extended in the ORCA 2 series, and offers very high logic capacity up to 40,000 logic gates.
ORCA 2 features a two-level hierarchy of PFUs based on the original ORCA architecture.