[Robotgroup] Processor with Hardware Encoder Support

[Paul Atkinson]

Eric,

Just a guess, but I think the interupt overhead becomes enormous with any respectable bit rate on the quadrature encoder. In many cases a dedicated processor that can just sit there waiting for a bit to flip is more efficient. (At least more efficient for the encoder counting task.)

There is also the issue of other tasks running on a single processor getting less CPU time as the encoder gets faster. If I understand the propeller, dedicating a cog or 2 for encoder handling would not affect the throughput on the other cogs. (I'm still not 100% sure there isn't some minor memory contention to be dealt with for the "rotating" thing in the center of all the cogs.)

Paul

----- Original Message ----
From: Eric Lundquist <eric.g.lundquist at gmail.com>
To: The Robot Group Mailing List <robotgroup at puremagic.com>
Sent: Wednesday, January 31, 2007 2:05:02 PM
Subject: Re: [Robotgroup] Processor with Hardware Encoder Support

One question I have is why the requirement for no interrupts?  I am
using an Atmel AVR to handle the two wheel encoders on one of my
robots specifically by tieing each one to an interrupt where I have a
couple lines of GNU C code to handle incrementing the encoder counter
in the Interrupt Service Routine.  The AVR also provides hardware PWM
(8 or 16 bit) via custom interrupt hardware.

At this point, I am not doing quadrature encoding but I don't need it
for this particular base.

The AVR's are a LOT cheaper than the Moto offerings. Atmel is pretty
good about supporting hobbyists and the GNU tool chain is very well
done for it.  There is also an active user community.

- Eric


On 1/31/07, vkonradi <vkonradi at swbell.net> wrote:
> I'm considering processors for a mobile robot.  A key feature I'd like to have is hardware encoder support, i.e. bolt up a quadrature encoder and the processor automatically increments/decrements a counter.  No interrupts, no external PLD, etc.
>
> The processor ought to support a minimum of 2, and preferably 4 or more channels, each consisting of encoder input + PWM output.
>
> All I have found so far are Freescale Coldfire (68K) and Embedded Power PC controllers which come with eTPU, enhanced time processing unit.
>
> Other suggestions?
>
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