Re: [Emc-developers] Parallel port alternatives

[Kirill 'B. K' K. <kk...@po...>]

>> HAL should make I/O through lots of peripherals possible.
>> The parallel port should, IMHO, be considered only one
>> of many possible I/O paths,

I am a fan of Cypress' AN2131 USB chip (as far as a concept of fandom of
an integrated circuit goes :)).  This is an 8051 clone with hardware USB
peripheral implementation.  Whenever I need a computer to do digital I/O,
I throw one of these in.  I ordered a lot of PCBs for them - with EEPROM
and a voltage regulator it forms a complete unit - and cook a few at
once when my stash ends. 

Realtime I/O is not possible with these, since there may be as large as
2ms gap between 2 successive USB transmissions (if one comes in the
beginning of the 1ms "window" and another is scheduled closer to its
end).  However, the controller is not dumb enough not to drive[1] a few
steppers with some the help from the CPU.

While that can certainly be implemented within the HAL framework, the
thing, with some tweaking of thread priorities and some luck, may
quite easily be used without a real-time core.  Sound processing, for
one example, has already became practical with audio buffer sizes of
1.5ms - and a user-mode thread feeds an audio card with these buffers
uninterrupted.

There are a few commercially available boards with the chip ($80+)

http://www.jged.com/web_pages/usbsimm.html
http://www.devasys.com/usbi2cio.htm

and some non-development arrangements, such as a USB-to-PS keyboard
dongle adapter, in the range of $20, that I do not have links to.

 -kkm

[1] I intended to write "intelligent enough to drive...", but that would
rather be an assault on reality.