Hi Toaster,
That was a phenominal post and I read every word of it!
For me, anyway, it has shed a lot of light on IRQ assignments and why some can't be changed by the user.
I have saved it for future reference. I know I may need it sooner rather than later

.
Once again thanks for a sharing this info with us! I know we 'mere mortals' here really appreciate the time it took for you to write it.....
I personally think it should be considered for 'The Hall of Fame'!
Yours
Declan (aka fredwest)