[atari7800] why are IRQs disabled?

I've recently noticed that all of the demos and examples I've seen use the 
"sei" instruction before initializing the 7800.  This disables interrupts.  
None of the examples use "cli" to restore them.  I'm doing the same thing in my 
code, but I'm not sure why.


1.  Why is it necessary to disable interrupts at this stage?

2.  Is it safe to leave them disabled forever?  This causes instability on x86 
PCs, but granted the 7800 is a simpler machine.

3.  Will the "brk" instruction be affected by this setting?

4.  Is there any source of maskable interrupts in the 7800 besides the "brk" 
instruction?  If so, then what are they?  If not, then what's the point of 
calling "sei"?

Thanks for any information on this.  I'd like to make sure my initialization is 
in proper form.


-Greg
-- 
_______________________________________________
Find what you are looking for with the Lycos Yellow Pages
http://r.lycos.com/r/yp_emailfooter/http://yellowpages.lycos.com/default.asp?SRC=lycos10

Other related posts: