Holger Wetter

The IBM eServer z990 floating-point unit

The floating-point unit (FPU) of the IBM z990 eServerTM is the first one in an IBM mainframe with a fused multiply-add dataflow. It also represents the first time that an SRT divide algorithm (named after Sweeney, Robertson, and Tocher, who independently proposed the algorithm) was used in an IBM mainframe. The FPU supports dual architectures: the zSeries® hexadecimal floating-point architecture and the IEEE 754 binary floating-point architecture. Six floating-point formats-- including short, long, and extended operands-are supported in hardware. The throughput of this FPU is one multiply-add operation per cycle. The instructions are executed in five pipeline steps, and there are multiple provisions to avoid stalls in case of data dependencies. It is able to handle denormalized input operands and denormalized results without a stall (except for architectural program exceptions). It has a new extended-precision divide and square-root dataflow. This dataflow uses a radix-4 SRT algorithm (radix-2 for square root) and is able to handle divides and square-root operations in multiple floating-point and fixed-point formats. For fixed-point divisions, a new mechanism improves the performance by using an algorithm with which the number of divide iterations depends on the effective number of quotient bits.

High performance floating-point unit with 116 bit wide divider

The next generation zSeries floating-point unit is unveiled which is the first IBM mainframe with a fused multiply-add dataflow. It supports both S/390 hexadecimal floating-point architecture and the IEEE 754 binary floating-point architecture which was first implemented in S/390 on the 1998 S/390 G5 floating-point unit. The new floating-point unit supports a total of 6 formats including single, double, and quadword formats implemented in hardware. The floating-point pipeline is 5 cycles with a throughput of 1 multiply-add per cycle. Both hexadecimal and binary floating-point instructions are capable of this performance due to a novel way of handling both formats. Other key developments include new methods for handling denormalized numbers and quad precision divide engine dataflow. This divider uses a radix-4 SRT algorithm and is able to handle quad precision divides in multiple floating-point and fixed-point formats. The number of iterations for fixed-point divisions depend on the effective number of quotient bits. It uses a reduced carry-save form for the partial remainder, with only 1 carry bit for every 4 sum bits, to save area and power.

14nm FinFET based supply voltage boosting techniques for extreme low V min operation

This paper presents new dynamic supply and interconnect boosting techniques for low voltage SRAMs and logic in deep 14nm FinFET technologies. The capacitive coupling in a FinFET device is used to dynamically boost the virtual logic and array supply voltage, improving Vmin. Hardware measurements show a 2.5-3x access time improvement at lower voltages and a functional Vmin down to 0.3V. Results are supported by novel physics-based capacitance extraction and novel superfast statistical circuit simulations.