The integrated FPU DSP (into the Cortex-M7 core) is using 2X the number of clock cycles when compared with the SHARC21489.
Thinking of selecting an ARM Cortex-M7-based Atmel SAM V70/71 for your next automotive entertainment application? Three key reasons to consider are the clock speed of the the Cortex-M7 (300 Mhz), the integration of a floating point (FPU) DSP, and last but not least, because the SAM V70/71 has obtained automotive qualification. If you delve deeper into the SAM V70/71 features list, you will see that this MCU is divided 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, what makes the SAMV70/71 so unique is its FPU DSP performance. 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. Take the Analog Device AD21489 or Blackfin70x series, for example. However, the automotive market is not only very demanding, it’s also a very cost sensitive market as well.
Think about this simple calculation: If you select AD21489 DSP, you will have to add external flash and a MCU, which would lead the total BOM to be four to five times the price associated with the SAM V71. (Let’s also keep this AD21489 as a reference in terms of performance, and examine 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
To elaborate upon that even further, this FIR is used to build equalization filter — the higher Taps count, the better. If we look at the “50 Taps” benchmark results, the SAM V71 (Cortex-M7 based) exhibits 22,734 clock cycles (about three times more than the SHARC21489). Unsurprisingly, the Cortex-M4 requires 50% more, but you have to integrate a Cortex-A15 to get better results, as both the Cortex-A8 and Cortex-A9 need 30% and 40% more cycles, respectively! 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 instance, when building eight channels and six 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 quite similar to those of the FIR benchmark: only the Cortex-A15 and the SHARC21489 exhibits better performance. The integrated FPU DSP (into the Cortex-M7 core) is using twice the amount of clock cycles when put side-by-side with the SHARC21489. If you compare the performance per price, the Cortex-M7 integrated in the SAMV71 is 50% cheaper! Using a SHARC DSP certainly makes sense if you want to build high performance home cinema system, but if you target automotive, it’s much more effective to select a FPU DSP integrated together with Flash (512KB to 2MB) and a full featured MCU.
The Atmel SAM V71 is specifically dedicated to support automotive infotainment application, offering Dual CAN and Ethernet MAC support. Other notable specs include:
- 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 looking to construct an automotive high-end radio, you still need room for Ethernet MAC and AVB support… What’s more, the SAM V71 only consume 68% of the DSP resource, leaving well enough space for both AVB and Ethernet MAC.
Interested? Explore the Atmel | SMART SAM V ARM Cortex-M7 family here. More information about the the DSP benchmark can be also found on DSP Concept’s website. Also, be sure the detailed DSP Concept’s audio processing benchmarks.
This post has been republished with permission from SemiWiki.com, where Eric Esteve is a principle blogger as well as one of the four founding members of SemiWiki.com. This blog first appeared on SemiWiki on May 6, 2015.
