Best GPIO API for high data rates and frequencies?

Question

Using RPI3B+. I need to have 2 pins (a clock and data) to write data to shift registers on frequencies of 1,76 MHz or rate of 1,76 Mbps, and 1 pin(connected to GPIO 18) on 20 kHz.

Tested RPi.GPIO.PWM on normal gpio pins but the response was this: Input frequency of 1000 Hz gave me about 850 Hz. 6000 Hz about 3200 Hz. It maxed out at a very unstable 6-7Khz with any extremely high number as input. So the purpose of that library is probably for lower frequencies.

[Question: Are other GPIO libraries better for creating PWM pins or writing data at these rates?]

[Edit]: I already use SPI0 for a LCD. I have 11 74hc595 shift registers daisy chained and want to have PWM output on their outputs on at least 20 kHz instead of just high and low. So I thought:

-Latch needs to be at least 20kHz.

-Clock and data synchronous on at least 8*(11 shift registers) * Latch speed = 1,76 MHz\ Mbps.

Answer 1

If you are driving shift registers SPI will be the most efficient as you need to synchronise clock and data.

PWM is pointless as you need to have a synchronised data feed.

Using Python is not sensible if you need speed.

You could bit bang both clock and data with a C library. I doubt you would reach 1.76 Mb/s but you'd be in the right order of magnitude.

You really need to explain exactly what you want to do. Sending continuously at 1.76 Mb/s is an order of magnitude harder then sending sporadically as fast as possible.