DRRA-2 Overview

The DRRA-2 design focuses on solving the problems faced by the DRRA-1 fabric. The DRRA-2 fabric is also a CGRA fabric similar to the DRRA-1 fabric. However, we do not distinguish storage and computation fabric anymore. Any cell in DRRA-2 can be either a computation cell, or a storage cell, or even a hybrid cell.

Inside each cell, there is a single cell-level controller called sequencer, just like the DRRA-1 cell. However, different from DRRA-1, there is no pre-designed resources in each cell. Instead, each cell has 16 resource slots, the system designer can plug in any available resources in any of those slots.

The cells in DRRA-2 fabric are connected by NoCs. We keep a simple nearest neighbor connection scheme instead of a sliding window scheme (used in DRRA-1) to simplify the interconnection cost.

The following figure shows the architecture of DRRA-2 fabric. Readers can clearly see the internal components in each cell.

The DRRA-2 ISA's instruction space is divided into two categories: controller instructions and resource instructions. The cell-level controller decodes the controller instructions. The resource instructions are sent to a specific slot inside the cell and will be decoded by the local controller in that slot. As shown in the following figure, The two-stage decoding process for resource instructions makes the instruction decoding logic extremely simple. On cell-level decoding, the controller simply forwards the instruction payload to a specific slot. While the slot-level controller only decodes 1 or 2 types of instructions that can run on the corresponding resources. Compared to a single-stage decoder like the controller in modern microprocessors, the DRRA-2 decoding scheme is much simpler.