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DSP Selection for battery-powered project

Started by Bob May 14, 2008
I have a project that needs a battery-life of 16-18 hours on 2-3
standard AA cells.  So we're talking about 150 mA, maybe.

As for processing load, it's not completely clear, but a reasonable
top-end is about 30-50 MIPS, of which 50% are adds/subs, 24%
multiplies, 25% shifts, and 1 % divisions.  These were measured with a
24-bit, fixed-point implementation; if a 16-bit DSP were to be used, I
would need to use two words, as I need probably 20 bits for the
dynamic range; hence, the numbers would approximately double, though
maybe a 1.5 factor could be accomplished.

My initial thought was the Freescale DSP56371, but that seems to be
targeted towards a couple of very high-volume customers, and would
likely have availability issues.  The other DSP563xx parts are
interesting, but there are so many!

Part cost is unclear, but I'm guessing $10-$20 in 10K quantities is a
reasonable starting point.

What do you recommend?  I'm mainly worried about power consumption,
though the processing is not totally insignificant...

Thanks,
-Bob
On May 14, 6:48&#2013266080;pm, Bob <rsg.uCli...@gmail.com> wrote:
> I have a project that needs a battery-life of 16-18 hours on 2-3 > standard AA cells. &#2013266080;So we're talking about 150 mA, maybe. > > As for processing load, it's not completely clear, but a reasonable > top-end is about 30-50 MIPS, of which 50% are adds/subs, 24% > multiplies, 25% shifts, and 1 % divisions. &#2013266080;These were measured with a > 24-bit, fixed-point implementation; if a 16-bit DSP were to be used, I > would need to use two words, as I need probably 20 bits for the > dynamic range; hence, the numbers would approximately double, though > maybe a 1.5 factor could be accomplished. > > My initial thought was the Freescale DSP56371, but that seems to be > targeted towards a couple of very high-volume customers, and would > likely have availability issues. &#2013266080;The other DSP563xx parts are > interesting, but there are so many! > > Part cost is unclear, but I'm guessing $10-$20 in 10K quantities is a > reasonable starting point. > > What do you recommend? &#2013266080;I'm mainly worried about power consumption, > though the processing is not totally insignificant... > > Thanks, > -Bob
you didn't mention memory requirements or peripherals required, which normally drives part selection. But you performance requirements aren't that high so you can use a low end DSP like micro, maybe a 32 bit AVR32 UC3 (40mA, 83MIPS) would work, or a ARM Cortex (STM32)
On May 14, 10:14 pm, steve <bungalow_st...@yahoo.com> wrote:
> you didn't mention memory requirements or peripherals required, which > normally drives part selection. But you performance requirements > aren't that high so you can use a low end DSP like micro, maybe a 32 > bit AVR32 UC3 (40mA, 83MIPS) would work, or a ARM Cortex (STM32)
Hmm... AVR32 - that's interesting... To fill in the missing information, we're not talking about a lot of memory - a few tens of kilobytes for data ram is sufficient, and the program code is also in the tens of kilobytes. Ideally, the memory would be on-chip. Even more ideally, Flash-based. But an on-chip bootloader coupled with an external serial EEPROM is okay too. I/O is relatively simple: 4-6 16-bit A/D and 2 16-bit D/A - it is assumed these will be external to the DSP, but simple interfacing would be important. Sample rates for these (and of course, the underlying algorithm) is about 10 kilohertz. Thanks again! -Bob
On May 14, 10:34 pm, Bob <rsg.uCli...@gmail.com> wrote:
> On May 14, 10:14 pm, steve <bungalow_st...@yahoo.com> wrote: > > > you didn't mention memory requirements or peripherals required, which > > normally drives part selection. But you performance requirements > > aren't that high so you can use a low end DSP like micro, maybe a 32 > > bit AVR32 UC3 (40mA, 83MIPS) would work, or a ARM Cortex (STM32) > > Hmm... AVR32 - that's interesting... > > To fill in the missing information, we're not talking about a lot of > memory - a few tens of kilobytes for data ram is sufficient, and the > program code is also in the tens of kilobytes. Ideally, the memory > would be on-chip. Even more ideally, Flash-based. But an on-chip > bootloader coupled with an external serial EEPROM is okay too. > > I/O is relatively simple: 4-6 16-bit A/D and 2 16-bit D/A - it is > assumed these will be external to the DSP, but simple interfacing > would be important. Sample rates for these (and of course, the > underlying algorithm) is about 10 kilohertz.
Yes, you might want to look at general purpose micros, especially if they can incorporate the ADC and DAC to suit your needs. As an external component, the ADC and DAC can add as much to the cost as the MCU. You might want to carefully consider the need for 16 bits. Or you might find that you can get the equivalent of 16 bits by oversampling and averaging. Then there are a lot of options of on chip ADC available. Also, you might want to consider the new TI floating point chip. I forget the number, but it is targeted to lower power and cost applications and I want to say it includes on chip flash. Then you can all *but* ignore the precision and range issues.