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Emulate USB?


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I still haven't gotten my launchpad (says it is shipping).

 

I am getting interested in programming USB, mostly from the computer side of things. My plan is to interface hardware via the 430 via a USB connection. I know they have firmware versions for Atmel but couldn't find anything for the MSP430 line.

 

Is there a already built firmware that emulates USB in software on the MSP430 value line?

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Currently, not that we know of. With similarly low spec Atiny's being able to pull usb duty, the msp430 valueline (atleast the upper spec'd ones) should be able too. Especially the newer ones (8kb code, 256 ram). One of the members here were able to get TV out just like the avrs did afterall.

 

The hard part though is the coding. Until someone can create such a firmware, or port one of the avr usb firmwares over, the only way to get usb cheap/simply is usb-serial adaptors, and those have their limits as simple terminal sessions.

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i'm no expert on the subject but imho, ram and flash are not the limiting factors, or else it would have been widely implemented on PICs as well. bit banging usb almost boils down to how quickly a chip can toggle a pin. i think avrs can do it in one clock cycle, so e.g. with a 12MHz crystal ~> 8 instruction breathing room, it's possible with some expert hand optimized assembly for near perfect timings.

 

even low speed usb devices (like mice/keyboard) would require 1.5Mbps... i think that would be difficult to emulate on a lowend msp430. first, the value line chips don't support high freq external crystals (maybe)... but you can still try with dco --- not sure how good it is. meanwhile you also need to handle the nrzi encoding and logic specific to your firmware.... also I think you need to drive two signals for usb (although, that doesn't necessarily mean double the work). I haven't studied the timings for msp430 yet (got my first launchpad yesterday), but already I see that a simple jmp takes two clocks and that's discouraging.

 

it would certainly be amazing if someone can do it. :o

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You could use an FTDI chip that does usb to serial. I've bought breakouts with them from sparkfun, but you might be able to get a better price if you dig around.

Or hack a Nokia phone cable for serial? (~$1-2 on eBay)

 

Good call, Doc. I forgot about that. I just bought 2 from eBay.

http://cgi.ebay.com/USB-DATA-CABLE-CA-42-CA42-CD-NOKIA-7260-6101-6100-/290425651135?pt=PDA_Accessories&hash=item439eb7bfbf

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Or hack a Nokia phone cable for serial? (~$1-2 on eBay)

Good call, Doc. I forgot about that. I just bought 2 from eBay.

I still need a bit of help on how to hack them. I bought two, and the drivers worked with the one I couldn't get to work; so now I have three ready to experiment with. :D

 

Any tips/links would be helpful (probably for pro547 as well ;) ).

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