Measuring frequency on Rpi 4

[jarekkt]

How have you been able to measure frequency on Rpi 4 ?

I have tried myself (with a bit more direct approach - kernel driver which stops whole CPU for the test period ).
If I do direct bit banging like this:

while(1)
{
GPIO_CLR = BV(4);
GPIO_SET = BV(4);
}

then the signal on pin is messed - as if pin current strength is too low to charge pin capacitance.

Something like this works better:

while(1)
{
GPIO_CLR = BV(4);
GPIO_CLR = BV(4);

GPIO_SET = BV(4);
GPIO_SET = BV(4);
}

Then the signal is readable - the frequency is about 52MHz ( checked on 200MHz scope)

Is there any control over Rpi 4 pin speed/strength ?

[weagle08]

I've observed the same on PI 4. The above modification works.

for (;;) {
    *set_reg = (1<<TOGGLE_GPIO);
    *set_reg = (1<<TOGGLE_GPIO);
    *clr_reg = (1<<TOGGLE_GPIO);
    *clr_reg = (1<<TOGGLE_GPIO);
}