Very informative response, thank you very much.
My conundrum for my project is I have to measure four pulse sources, currently I have one on d2(int0) and one on d4(int1) I need two more. which is why I was looking for a "soft" interrupt.
I have to be careful in mucking about because I also have serial data back and forth (on d0,d1), pwm on 4 pins(d5,d6,d10,d11) and several addressables running on the I2C bus on pins a4 and a5.
EDIT: So upon further review, the clear answer is not with out mucking up a bunch of other stuff already using timers and interrupts.
Prolly goinng to move to some other hybrid answer from here.
Thanks again
Boz