gnupic@linuxhacker.org

On Wednesday 07 May 2003 05:29, Charles Lepple wrote:
> On Tuesday, May 6, 2003, at 11:20  PM, Mark Gross wrote:
> > Look at what it would take to add support for other processors (AVR,
> > 8051, the
> > USB enabled PIC16C765/JW - 2 PIC I'm getting samples for ;)
>
> I'm not sure if Microchip has an ICE for this processor, but if not, I
> can tell you from experience that you will want to put a ZIF socket on
> your board, and have about 5 or 6 of the windowed chips handy when
> debugging.
>
> While I'm not saying that you couldn't write a decent USB app with this
> chip given enough time, it's a real pain. I suppose a HLL could help,
> but once you've used a chip with a "real" USB SIE (such as the EZ-USB
> series, which handles a lot of layers of the USB protocol in hardware)
> you may never go back. The PIC SIE makes you do everything by hand, and
> the sample code relies heavily on banking and paging (which I find
> difficult to debug without a simulator). Plus, several months ago when
> I started working on my code, gpasm didn't support relocatable objects,
> and therefore wouldn't assemble Microchip's sample code without a lot
> of help (read: hand editing). I trust the situation is better now, but
> haven't verified it.
>
> Also, these chips are low-speed, which makes them even slower than
> serial once you subtract out the protocol overhead. Granted, you do get
> some nice error detection and insertion/removal events from the  USB
> stack, but what's hidden in the fine print is that low-speed HID
> devices (the easiest to interface to under Windows) get only 800
> bytes/sec per HID report ID. I say "low-speed" and not "1.5 Mbps"
> because 1.5 Mbps is only the signaling rate, and only a small portion
> of the available bandwidth is allocated to low-speed devices.
>
> I don't want to intentionally rain on your parade, honest-- I just feel
> that I got bitten by brand loyalty when I started down the path with
> USB-enabled PICs. Although the EZ-USB chips aren't as free-standing as
> a PIC (needing at least an LDO regulator and possibly some power-on
> reset circuitry), they are definitely a strong contender if you just
> want to get a USB design off the ground with minimal hassle. Oh, and
> SDCC works great with the EZ-USB chips.
>
> I will probably give the upcoming USB-enabled 18F series chips a
> chance, but the 16C765 disappointed me.


Wow!  thanks for the info!  You may have saved me a lot of wasted time.  
Thanks!  

BTW what I'm thinking of trying is to re-design the Mark-III 
http://www.junun.org/MiniSumoMarkIII/ controler card to use USB over rs-232.

--mgross