indeed Bruce.

Consider I might be aiming at a portable device, or other low power, low count silicon platform. (5$)
and bear  in mind, I might want a heap processing power left over for  modulator/demod, error correction, some audio processing , noise reduction etc.

For those that know real DSPs, they'll recognize that the Cortex M4 (stm32 4...) is NOT a real DSP. It has some handy instructions, they call DSP, sure. But start throwing it alot of filtering tasks and you'll run out of cycles.

It is a very good general purpose processor though, excellent  in fact. I use it for all sorts of things when I don't care about power consumption. The CODEC2 is not a simple DSP task, it is much more a complex algorithm that doesnt get alot of help from a real DSP. The STM32M4  is not a low power processor.
A real FP processor like the latest low power SHARCs ($10) for similar money might do the job for less power, depending on the efficiency of the coder- that's the thing to get the advantage of the real DSP, you got to know what you are doing. The M4 will make fairly good throughput out of junk coding.  I use the Rowley Associates toolchain.


glen english
VK1XX
"yes - I do this for a living"
Altium- ModelSim, Matlab, Vivado, Rowley.

On 21/08/2014 5:44 AM, Bruce Perens wrote:
The reasoning is indeed that floating point is easier to develop and that our development time is more expensive than CPUs.We don't know the table sizes offhand.

However, the assumption that both of the codec and modem would fit in really small and relatively low-power floating point chips was optimistic and as of this moment it's right on the edge of working in the STM32F405 that David has built into his SmartMic project. The STM32F405 is an ARM Cortex M4F at 168 MHz, 1 MB FLASH, 126K instruction/data RAM, and 64K data RAM.

Over the past weeks David has torn through the code working on optimization, and at this moment the receive speed is "borderline".

    Thanks

    Bruce

CPOn 08/20/2014 11:42 AM, Steve wrote:
I think the reasoning is, that floating point and memory are so cheap now, that trying to fit a design into a restricted space would just lengthen the time to profit.

Why design to a fixed point $30 DSP when you can buy a $5 CPU with hardware FP.

73,Steve


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