I can't get interrupt on Atmega8A to work, what does Arduino support ?
Page 68 of the data sheet starts the discussion of interrupts.
It looks like the interrupts should work fine on the ATmega8A. Pin 2 for Interrupt 0 and Pin 3 for Interrupt 1, same as for the ATmega168 and ATmega328P. What symptoms are you seeing?
Simply nothing would cause the interrupt, I tried D9..D11 and A5 (I am using Cheapduino due to it's size, so pin2/3 are not easy to access)
I were using attachInterrupt(digitalPinToInterrupt(A5), Blink, RISING);
Only Pin 2 and Pin 3 have external interrupts.
Do you really need such a small form factor?
You can get five Arduino Nanos for $13.95 ($2.79 each) on eBay: https://www.ebay.com/itm/5Pcs-USB-CH340G-Nano-V3-0-16M-5V-ATmega328P-Micro-Controller-Board-For-Arduino/222545056262 (or 15 for $2.594 each) . They include a USB-to-Serial interface and access to all 20 I/O pins.
The $3.45 "Arduino Pro Micro" has USB plus a spare serial port.
"such small" is in this case rather large, but perfectly able to fit inside the cameras I modify. I do modify some compact cameras for proper control & feedback for UAV. That involves some micro soldering about three wires per mm, so I could/should rather design my own, even smaller board, but procrastinated it due to the availability of cheapduino in the development phase.
ATmega8 has the "external interrupt" capability (on pin 2 and 3), but does NOT have the "Pin Change interrupt" that allows "attachinterrupt()" to work on additional pins of the ATmega328.
Cute board, that Cheapduino. I wonder why they're not selling a version with one of the newer chips (which AFAIK are pin compatible even in the tiny packages.)