Embedded Linux questions

[Alan Dayley]

Well, we are suddenly getting down to serious decision time at my 
employer.  We are designing a product that potentially could have embedded 
Linux.  Some questions have come up.

1 - If I have my specific embedded application task running and only the 
absolutely required system tasks, what is the minimum and maximum latency 
from a switch out of my task and back into my task?  I know a definitive 
answer here is dependent on what tasks are running so my question is vague 
at best.  What we need at the moment is some sort of ball-park figure to 
know if Linux is simply possible for our needs.

2 - Connected to the question above, would a real-time Linux solve this 
question with hard latency times?

3 - If we cannot use Linux embedded, we will be using our own task 
switching kernel as the embedded "OS"  and we could us DOS as our 
development platform with the development embedded app running as a DOS 
app.  I would rather not use DOS as the development platform since it is a 
limited platform.  How difficult is it to create a Linux app that allows 
direct writes to I/O space and stack context switching while still running 
as a Linux app?  This would be for the development environment, allowing 
debugging etc. on the Linux platform and then making the app PROM bootable 
and loadable before moving it into the target product.  We can do this sort 
of setup now in DOS.

Hey, if you can't answer my questions because they are too general and 
could fill a book, just point me to the book(s), online or on dead tree media.

Alan