What is Real SAMV71 DSP Performance in Auto Audio?

Why selecting ARM Cortex-M7 processor based Atmel SAMV70/71 for automotive entertainment application? The top three reasons are the Cortex-M7 clock speed (300 Mhz), the integration of a floating point (FPU) DSP and, last but not least because Atmel SAMV70/71 has obtained automotive qualification. If you dig into SAMV70/71 features list, you see that this MCU is declined into several versions integrating Flash: 512 KB, 1024 KB or 2018 KB. And if you compare with the competition, this MCU is the only Cortex-M7 supporting the 2 MB Flash option, being automotive qualified and delivering 1500 CoreMark (thanks to the 300 MHz clock speed when the closest competitor only reach 240 MHz and deliver 1200 CoreMark)…

In fact which makes the SAMV70/71 unique are the FPU DSP performances. Let’s make it clear for the beginning, if you search for pure DSP performance, it will be easy to find standard DSP chip offering much higher performance, like for example Analog Device AD21489 or Blackfin70x series. But the automotive market is not only very demanding, asking for specific qualification, it’s also a very cost sensitive market. A simple calculation shows that, would you select AD21489 DSP, because you have to add external flash and a MCU, the total BOM would be x4 if not x5 compared with the SAMV71 price. Let’s keep this AD21489 as a reference in term in performance, and take a look at DSP benchmark results, coming from third party DSP experts “DSP Concept”.

Before analyzing the results, we need to describe the context:

• FIR is made on 256 samples block size
• Results are expressed in term of clock cycles (smaller is better)
• All DSP are floating-point except Blackfin
• Clock cycles count is measured using Audio Weaver

Some more explanation, this FIR is used to build equalization filter, the higher Taps count the better will be the equalization filter. If we look at the “50 Taps” benchmark results, the SAMV71 (Cortex-M7 based) exhibits 22734 clock cycles (about three times more than the SHARC21489). The Cortex-M4 needs 50% more, which is not surprising, but you have to integrate a Cortex-A15 to get better results, as both Cortex-A8 and Cortex-A9 need respectively 30% and 40% more cycles! And when looking at standard Analog Devices Blackfin DSP, only the 70x series is better by 35%… the 53x being 30% worst.
Now, if you want to build a graphic equalizer, you will have to run Biquad. For example, if you want to build 8 channels and 6 stages graphic equalizer, your DSP will have to run 48 Biquad.

Again the context:

• Biquad is made on 256 samples block size
• Results are expressed in term of clock cycles (smaller is better)
• All DSP are floating-point except Blackfin
• Clock cycles count is measured using Audio Weaver

In fact the results are very similar to the FIR benchmark results: only the Cortex-A15 and the SHARC21489 exhibits better performances. The integrated FPU DSP (into the Cortex-M7 core) is using 2x the number of clock cycles when compared with the SHARC21489. If you compare the performance per $, the Cortex-M7 integrated in the SAMV71 is 50% cheaper! Let’s say that using a SHARC DSP certainly makes sense if you want to build high performance home cinema system, but if you target automotive, better to select a FPU DSP integrated together with Flash (512KB to 2MB) and a full featured MCU.

Atmel SAMV71 is specifically dedicated to support automotive infotainment application, offering Dual CAN and Ethernet MAC support and this complete features list:

• 10/100 Mbps, IEEE1588 support
• 12 KB SRAM plus DMA
• AVB support with Qav & Qas HW support for Audio traffic support
• 802.3az Energy efficiency support
• Dual CAN-FD
• Up to 64 SRAM-based Mailboxes
• Wake up from Sleep or Wake up Modes on RX/TX

Don’t forget that when you have built this automotive high end radio you still need room for Ethernet MAC and AVB support… And the SAMV71 only consume 68% of the DSP resource, leaving well enough for AVB and Ethernet MAC.

More information about this DSP benchmark can be found on DSP Concept web here.

From Eric Esteve from IPNEST