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Re: [rtl] *Fast* IRQ response scope gif images
http://aol11.wff.nasa.gov/sra/images/d002.gif
is a screen capture of the scope showing interrupt response time on our
system. The top trace is the actual IRQ-5 signal line. The bottom trace
is is the signal generated by the interrupt procedure:
void intr_handler(void) {
outb(0xff, 0x378);
outb(0, 0x378) ;
}
which generates a pulse on the printer port data bits. The scope was set
to the "persistent mode" which makes it keep all traces on the screen
until you clear them. This image shows the variation in response time for
967 interrupts. What the scope does not show easily is that most
responses are just over 2us and a few are 4-6us late.
http://aol11.wff.nasa.gov/sra/images/d003.gif
shows the same thing, but with a slightly different time scale and not as
many sweeps.
The interrupts are being generated by a PIC chip (see www.microchip.com)
which is directly connected to IRQ-5 on my system. The system is a 200mhz
P5 with 64mb ram. It's a single-board thing from Industrial Computer
Systems with onboard scsi, ide, vga, etc. etc.
-W. Wright
--- [rtl] ---
For more information on Real-Time Linux see:
http://rtlinux.cs.nmt.edu/