Can the 19.2MHz be divided accurately enough by the PWM or GPCLK0?
To answer half my own Question, No.
The GPCLK's only have 12 bit dividers.
So 19.2MHz /4095 = 4688Hz is nowhere close enough to 15-120Hz required for a IR LED strobe pulse unless an extra divider is used.
Found this out using Ultibo but it looks like Gordon's WiringPi which was ported to Ultibo will work in Raspbian etc
pinMode(1, GPIO_CLOCK) will setup pin 18 as the GPCLK0.
There are two unknown? clock sources testdebug0/1. Are these I/O pins? JTAG CLK?
Not sure if GPCLK1/2 are free to use, have GPCLK1 outputting to pin 5, feed it back into pin 6 as JTAG-CLK/debug clock?
With two GPCLK's in series should get real accurate clock out of GPCLK0 for a LED strobe but only 50% duty cycle.
So now time to figure out the PWM hardware.
There are solutions already in software and external hardware for IR strobes, but the point of me doing it this way is to learn the Pi's hardware. And to make a simple IR strobe for night use of Pikrellcam.