[sdiy-interim] FLASH/JTAG based DSP?

[Eric Brombaugh]

On Mar 24, 2007, at 7:08 PM, Nicholas Gregorich wrote:

>
> On Saturday, March 24, 2007, at 06:49PM, "Batz Goodfortune" 
> <batzman-nr at all-electric.com> wrote:
>> Y-ellow All.
>>         Adam and I continued out discussion of the Propeller chip 
>> off-list
>> given that the list was down. It's probably a bit stale to rekindle 
>> that
>> thread but it has me wondering.
>>
>> Is there a DSP that is FLASH based and programmable via JTAG or serial
>> port? Basically, a DSP that's as easy to work with as an AVR etc. 
>> We've
>> never heard of such a thing but that's not to say one doesn't exist. 
>> Or
>> maybe it's just crap and that's why no-one uses it.
>>
>> It would help if it were audio-centric and 32 bits wide but even 16 
>> bits
>> would be workable. Maybe just an I2C port or some SPI/I2C/serial 
>> ports. But
>> mainly the ability to program in circuit.
>>
>> Anything out there?
>
> You could try the dsPIC. It features almost everything you mention and 
> is cheap and easy to get into. I don't know how powerful they are 
> relative to other "real" DSPs.

I've used dsPIC - it's got a nice assembly language and plenty of 
peripherals. A GNU-based C compiler is available from the manufacturer, 
but the free version has time-limited optimization. A full freeware 
based toolchain is also available but  requires a bit of linux-foo to 
get going.

Programming tools range in price - the manufacturer's 
programmer/debugger is very nice but costs in the $160 range. 
Lower-priced 3rd-party  tools are also available but tend to be a bit 
persnickety about which devices they'll deal with.

One caveat - Batz specified JTAG programmability and dsPICs use a 
proprietary serial programming/debugging system. Some of the newer 
versions are supposed to be JTAG-able, but the latest errata sheets 
indicate that this feature is non-functional.

Performance-wise, the dsPIC is pretty decent. It is a 16-bit processor, 
so the DSP hardware will limit your SNR for those with audiophile 
aspirations. Instruction speed is limited to 30-40MIPs depending on 
which version you get, but you can get quite a lot of stuff done at 
that rate. I don't know how that compares to other DSPs in the same 
price range, but it's probably a bit underpowered compared to your 
midrange ADI & TI parts which tend to be pretty fast these days.

> FPGAs are also worth a look.

True. And the cost of entry is getting more reasonable all the time.

Also, at the risk of sounding like a broken record, I'd recommend the 
ADI ADuC702x series of parts. They're less than $10, sport decent 
peripherals (UART, SPI, I2C, ADC, DACs) and an ARM7TDMI running at 
45MHz. Programmable with either UART bootloader, or a full JTAG setup. 
62kB of on-chip program flash and 8kB of SRAM too. Free C compilers 
available and industry-standard processor. Definitely worth a look.

Eric


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