Re: [Emc-developers] how long is too long to be without interrupts

[Sebastian K. <se...@hi...>]

John Kasunich wrote:
> Kenneth Lerman wrote:
>> Why not do the GPIO from the fast thread, but not do all of it every 
>> time through the thread? If there are 16 GPIOs, do a different one each 
>> time through the thread. (I seem to remember some stuff on the Lunar 
>> Module doing things like this.)
>>
>> In effect, you would be creating a new type of slow thread that was 
>> synchronized with the fast thread.
> 
> This whole thing started because of a desire to be able to send fast 
> signals (step pulses or encoder signals) through those GPIO pins.  If 
> each individual pin is only updated every 16th time through the fast 
> thread, that isn't much different than accessing all of them in the slow 
> thread.

Kenneth's suggestion is like Jon Elson's suggestion.

With HostMot2 the minimum number of GPIOs that make sense to read at one 
time is 24.  The Anything I/O boards have 24 I/O pins on each I/O 
connector, and each connector is accessed through one 32-bit register 
(with 8 unused bits at the top).

Reading GPIOs starts with two address cycles, followed by some integer 
multiple of 4 data cycles (4 data cycles per group of 24 gpios).  Making 
more smaller reads means doing more address cycles, slowing things down. 
  And EPP is already so painfully slow, i think this doesnt work well.


-- 
Sebastian Kuzminsky
Cryogenic travel has improved since then...  I woke screaming in a
translucent box.  “There, there,” said the box. “Everything will be all
right. Have some coffee.”  -- Ken Macleod, "Who's afraid of Wolf 359"
<http://outofthiseos.typepad.com/blog/files/KenMacleodWhosAfraidofWolf359.htm>