Re: MCU/DSP dsPIC Alternatives?

From: Jack Klein (jackklein_at_spamcop.net)
Date: 03/26/04 

Date: Thu, 25 Mar 2004 20:38:01 -0600

On Wed, 24 Mar 2004 20:17:44 -0800, Chris Carlen
<crobc@BOGUS_FIELD.earthlink.net> wrote in comp.arch.embedded:

> Hi:
>
> I'm looking for DSP-like microcontrollers and microcontroller-like DSPs.
>
> So far I am interested in TMS320F2812, but it is a bit heavy handed for
> some applications I would be considering.
>
> I had decided to move away from Microchip a few years ago and instead
> standardize on AVR for my 8-bit MCU of choice, mainly because of avr-gcc
> and the AVR architecture is much more pleasant to work with. My
> applications are ease of use and tool cost conscious more than anything,
> so I don't mind the slightly higher price of AVRs.
>
> But I will be needing some DSP capabilities. I would like to find a CPU
> that gives reasonable performance of 30-150MIPS with lots of MCU
> peripherals. The dsPIC and the TI are the ones I am aware of so far.
>
> I spent some time lately looking at the dsPIC again, and despite my
> wanting to avoid Microchip and their klunky architectures, I have to
> admit this chip seems dsPICable, er, I mean pretty nice. But the darned
> thing appears to be vaporware!
>
> Anyway, I will be attending a 1-day workshop with TI on the TMS320F2812,
> and getting a development kit.
>
> As for Microchip, I guess we'll just have to wait.
>
> Any other recommendations for MCU-like DSPs and DSP-like MCUs? I don't
> really like the idea of going to Motorola, since I have heard their
> tools are a headache (needing to but a different tool for each chip) and
> I never know if their chips are going to be discontinued tomorrow.
> Other than those objections, I do know they have some nice DSP/controllers.
>
> Another idea I suppose for the 30-150 MIPS range might be ARM, since I
> know it has some MACs and stuff like that. Haven't really researched
> ARM much yet.
>
> I sure hope the market drives the production of more of these hybrid
> DSP/MCU type chips in the future.
>
> Thanks for comments.
>
>
> Good day!

I can't speak for many of the others, but we are developing a few
boards with the TI 2812 right now.

TI did a really good job taking the very traditional DSP instruction
set of their 24xx series and not just extending it, but turning it
into pretty good 16/32 bit RISC implementation. Unlike most DSPs, the
instruction set is very friendly to general purpose coding, and the
Code Composer Studio version for the 28xx generates excellent code for
it.

Just as an example, the 24xx parts had a bank of 16-bit auxiliary
register file, AR0 through AR7. They were very awkward to use in that
family, as you needed to set the ARP (Auxiliary Register Pointer
register) to specify the register you wanted to access, then you could
access it.

In the 28xx family, they not only extended the auxiliary registers to
32 bits (or they can still be used as 16 bits), but they made them
directly addressable. When you run the chip in its native 28xx mode,
the ARP is a useless and unneeded appendix, only there if you want to
run code from the older processors in 24xx execution mode.

The only "gotcha" that any reasonably experienced programmer would
need to be aware of when writing C or C++ code for these parts is the
lack of an 8-bit data type. The character types all have 16 bits. 

-- 
Jack Klein
Home: http://JK-Technology.Com
FAQs for
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http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html

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