HIgh speed GPIO

[thomasx]

Hi

I have noticed that there are some different libraries and software out there that makes the ESP32 output VGA.

One lib offers 640x480 resolution at 60Hz framerate. So this means a pixel rate of more than 18MHz, or about 50 nS per pixel.

While the ESP32 is also doing other stuff.

So I made a simple program that just toggled a GPIO on/off.

Basicly like this

Code: Select all

while(1) {
	  digitalWrite(Outpin,LOW);
	  digitalWrite(Outpin,HIGH);
}

But it's nowhere near the speeds needed to output a VGA signal.

So, I would like to start off by learning the basics on how to output signals with such high speed as a VGA signal.

Can someone please point me in the direction where I can find information/tutorials to start learning about this?

Just toggling a pin at 18MHz, or faster, and to understand what goes into making that happen, would be a good start.

Thanks!

[ESP_Sprite]

You could open those libraries to see what they do, most of them are open-source... but I imagine they all will be using some kind of DMA-enabled parallel output functionality. On the ESP32, that would be the LCD mode of the I2S peripheral, on the ESP32S3 it will be the LCD/camera module, etc.

[mikemoy]

Look into

GPIO.out_w1ts
GPIO.out_w1tc
GPIO.out1_w1tc.val
GPIO.out1_w1ts.val

You can control IO a LOT faster.

[liaifat85]

By configuring a timer to interrupt at regular intervals, you can toggle GPIOs with high precision.

[ESP_Sprite]

By configuring a timer to interrupt at regular intervals, you can toggle GPIOs with high precision.

That very much depends on what you call 'high precision'. Interrupt latency is a thing, and GPIO writes can get 'stuck' between other transactions on the bus. It's best to look at what peripherals can do for you without CPU interaction if you want high precision.

[mtraven]

I run "fabGL" on a couple esp32 projects, driving a 15" display @ 640*480. Color's must be limited to a pallet of 16, but it will work. LVGL is another good graphics library, though I've not tested it with a VGA display.

I'm a little unclear as to what you're trying to do? Make your own graphics library? No offense, but if you're still writing code in an arduino framework, as it sounds like you are, you're not ready to write your own graphics library.

If you're just playing around, wanting to find a fast way to write pins you could switch to a native IDF project & eliminate the middle man that is the arduino framework.

Or, the simpler option, have a look at a library like fastDigitalRead. There are a bunch of "fast io" libraries available for arduino. As I recall, some where VERY effective. Usually they give up some naming convenience / flexibility. If you are on a path to try to make your own graphics library, I suggest your start with your own fast GPIO library. That will get you familiar with direct register manipulation.


oh and FYI, VGA use analog signals, so digitialWrite() really has no place there anyways. On that note, you need to choose your pins such that they are connect to PWM capable pins.

[MicroController]

VGA use analog signals, so digitialWrite() really has no place there anyways. On that note, you need to choose your pins such that they are connect to PWM capable pins.

PWM is likely not an option for VGA signals. Instead, people tend to use a couple of resistors to build a simplistic DAC, enabling the use of e.g. 2 digital pins to generate one analog signal of 4 different voltage levels.