A 400-MHz S/390 microprocessor

A microprocessor implementing IBM S/390 architecture operates in a 10 + 2 way system at frequencies up to 411 MHz (2.43 ns). The chip is fabricated in a 0.2-μm Leff CMOS technology with five layers of metal and tungsten local interconnect. The chip size is 17.35 mm × 17.30 mm with about 7.8 million transistors. The power supply is 2.5 V and measured power dissipation at 300 MHz is 37 W. The microprocessor features two instruction units (IU's), two fixed point units (FXU's), two floating point units (FPU's), a buffer control element (BCE) with a unified 64-KB L1 cache, and a register unit (RU). The microprocessor dispatches one instruction per cycle. The dual-instruction, fixed, and floating point units are used to check each other to increase reliability and not for improved performance. A phase-locked-loop (PLL) provides a processor clock that runs at 2 ×the system bus frequency. High-frequency operation was achieved through careful static circuit design and timing optimization, along with limited use of dynamic circuits for highly critical functions, and several different clocking/latching strategies for cycle time reduction. Timing-driven synthesis and placement of the control logic provided the maximum flexibility with minimum turnaround time. Extensive use of self-resetting CMOS (SRCMOS) circuits in the on-chip L1 cache provides a 2.0-ns access time and up to 500 MHz operation.