Satisfying a clock skew constraint is one of the most important tasks in clock tree synthesis. Moreover, the task becomes much harder to solve when the clock tree is designed in a multiple power mode environment, in which the voltage applied to some design module varies as the power mode changes. Recently, it has been shown that an adjustable delay buffer (ADB), whose delay can be tuned dynamically, can be used to solve the clock skew problem effectively under multiple power modes. However, due to the area or control overhead by ADBs, it is very important to minimize the number of ADBs to be allocated. This paper provides a complete solution to the problem of clock skew optimization using ADBs under multiple power modes. We propose a linear-time algorithm that simultaneously solves the problems of computing: 1) the minimum (optimal) number of ADBs to be used; 2) the location where each ADB is to be placed; and 3) the delay value of each ADB to be assigned to each power mode. Experimental results show that, in comparison with the previous work, which iteratively performs the ADB allocation, placement, and value assignment, our integrated algorithm produces consistently better designs for all tested benchmarks; it reduces the numbers of ADBs by 9.27% on average under the skew bound of 30-50 ps, even with shorter clock latencies compared to that of previous algorithm of ADB allocation, placement, and delay assignment. To make it practically feasible, we also propose a new ADB design technique and systematic algorithmic solutions to address the problems of discrete delay values, slew rate variation, nonzero initial ADB delay, and a possible exploration of ADB resizing.

Satisfying clock skew constraint is one of the most important tasks in the clock tree synthesis. Moreover, the task becomes much harder to solve as the clock tree is designed under multiple power mode environment, in which the voltage applied to some design module varies as the power mode changes. Recently, it is shown that adjustable delay buffer (ADB) whose delay can be tuned dynamically can be used to solve the clock skew problem effectively under multiple power modes. However, due to the area/control overhead by ADBs it is very important to minimize the number of ADBs. This work provides a complete solution to the problem of clock skew minimization using ADBs under multiple power modes. We propose a linear-time optimal algorithm that simultaneously solves the problems of computing (1) the minimum number of ADBs to be used, (2) the location at which each ADB is to be placed, and (3) the delay value of each ADB to be assigned to each power mode. Experimental results show that in comparison with the previous work [8] which iteratively performs the ADB allocation, placement, and delay assignment, our integrated algorithm produces consistently better designs for all tested benchmarks under four power modes, reducing the number of ADBs by 9.27% further on average at skew bound of 30ps~50ps even with shorter clock latencies.

Distributed register-file microarchitecture (DRFM) which comprises multiple uniform blocks (called islands), each containing a dedicated register file, functional unit(s) and data-routing logic, has been known as a very attractive architecture for implementing designs with platform-featured on-chip memory or register-file IP blocks. In comparison with the discrete-register based architecture, DRFM offers a higher degree of opportunity of reducing the cost of global (inter-island) connections by confining as many the computations to the inside of the islands as possible. Consequently, for DRFM architecture, two important problems to be solved effectively in high-level synthesis are: (problem 1) scheduling and resource binding for minimizing inter-island connections, and (problem 2) data transfer (i.e., communication) scheduling through the inter-island connections for minimizing the access conflicts among the data transfers. This work proposes novel solutions to the two problems. Specifically, for problem 1 previous work solves it in two separate steps: (i) scheduling and (ii) then determining the inter-island connections by resource binding to islands. However, in our algorithm called DFRM-int, we place primary importance on the cost of interconnections. Consequently, we minimize the cost of interconnections first to fully exploit the effects of scheduling on interconnect and then to schedule the operations later. For problem 2, previous work tries to solve the access conflicts by forwarding data directly to the destination island. However, in our algorithm called DFRM-com, we devise an efficient technique of exploring an extensive design space of data forwarding indirectly as well as directly to find a near-optimal solution. By applying our proposed synthesis approach DFRM-int+DFRM-com we are able to reduce the inter-island connections by 18.1% more, compared to that by the DRFM approach in [4], even completely eliminating register-file access conflicts, which could never been resolved by [4], without any latency increase.