BDTI has released the first independent benchmark results comparing the performance of the Sandbridge “Sandblaster” SB3500 multi-core DSP chip to that of massively parallel chips, high-performance DSP processors, and FPGAs.
Sandbridge Technologies, Inc. is a fabless semiconductor company that sells multi-core chips targeting mobile 3G and 4G baseband and multimedia processing. The SB3500 chip includes three DSP cores along with an ARM core; each of the DSP cores supports four-way multithreading and 16-way SIMD operations. The SB3500 is implemented in a 65 nm process, and is available with the DSP cores running at either 500 or 600 MHz. The 500 MHz chip costs $25 in 1K quantities; pricing for the 600 MHz chip has not yet been disclosed.
BDTI evaluated the SB3500’s performance using the BDTI Communications (OFDM) Benchmark™. This benchmark is an application-oriented benchmark based on a simplified orthogonal frequency division multiplexing (OFDM) receiver, as shown in the block diagram below. The SB3500 benchmark implementation uses a combination of C and assembly code.
Figure 1: BDTI Communications Benchmark (OFDM)™: Simplified Block Diagram
BDTI has used the BDTI Communications Benchmark (OFDM) to evaluate a range of processing engines that target communications applications, including massively parallel processors, high-performance DSP processors, and high-performance, DSP-oriented FPGAs.
For this benchmark, BDTI typically reports two sets of results: low-cost results, which are optimized to provide the lowest cost per channel; and high-capacity results, which are optimized to accommodate the maximum number of channels per chip. A chip vendor may use two different chips to generate these two results. As of this writing, however, Sandbridge has only benchmarked one of its chips, so its high-capacity and low-cost results are the same.
The SB3500 is the first handset-oriented chip for which BDTI has published certified results on this benchmark, and its results are quite strong. The 500 MHz SB3500 can handle a total of six OFDM channels using its three DSP cores. Each of the cores runs four threads, with each thread running at 125 MHz. The OFDM benchmark is implemented by splitting each channel’s processing across two threads. This design allows each core to process two real-time channels for a total of six channels. The input data rate for each channel is 20 MSamples/second, and the Sandbridge implementation imposes a two-frame latency.
BDTI has previously published OFDM benchmark results for two massively parallel chips, the 866 MHz Tilera TILE64 and the 160 MHz picoChip PC102. These chips are designed for infrastructure applications rather than mobile applications, so it is perhaps not surprising that they support more than double the number of channels supported by the SB3500 (15 channels for the Tile64 and 14 for the PC102). The TILE64 and PC102 are also, however, significantly more expensive than the $25 SB3500: the TILE64 costs $890 and the PC102 costs $95 (all pricing is for 1K quantities). As a result, the SB3500 has the best cost-per-channel result among these three processors, and indeed, it has the lowest cost-per-channel result of any processing engine BDTI has evaluated to date, with the exception of high-performance FPGAs—which are typically too big and too expensive to be used in handsets.
Compared to a traditional DSP processor family, Texas Instruments’ ‘C64x+, the Sandbridge chip is both more powerful and much cheaper. At 1.2 GHz, the high-performance ‘C6455 can only handle 1-2 channels of BDTI’s benchmark. And the cost-per-channel result of the cost-optimized ’C6410 is an order of magnitude higher than that of the SB3500. (For detailed OFDM benchmark results, visit http://www.BDTI.com/OFDM)
Today, typical solutions for handset baseband and multimedia processing use a lot of specialized, fixed-function hardware. Sandbridge’s SB3500 does not. This difference may give Sandbridge users an advantage in terms of flexibility, but BDTI doesn’t yet have enough data for fixed-function solutions to be able to make comparisons based on performance, cost, and power. Based on our benchmark results, however, the SB3500 appears to be a strong new addition to the field, and may well prove attractive for the handset space.
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