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nopnop2002 / esp-idf-parallel-tft

8bit parallel TFT & 4-line resistance touch screen Driver for esp-idf using i2s paralell mode
MIT License
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QUESTION: SPI or parallel for new designs? #18

Open marcdraco opened 3 years ago

marcdraco commented 3 years ago

Not sure how else to post this, so I hope this isn't too off-topic. Let's assume that I'm designing a new board (or two) based on an ESP32 module. I have one of the WROOM devboards - but the new design will likely use an S3 when they drop.

Assuming there are enough free GPIOs left, is parallel preferable over SPI? (I'm only enough to remember the days that we thought parallel was the Dog's Danglers and Serial was consigned to telephones. (Data skew? What's that?! Electrons will never travel that fast and IBM PCs will never penetrate the home!)

So yeah, serial has a place - but I'm curious, is there any particular reason to use SPI over parallel on a new design (one that I can just drop a TFT into?)

My only experience is with the Arduino framework and that largely insulates us from the nitty-gritty but this needs I2S and some serious beef so short of going full SBC with all the uses they come with, I figured the ESP32 is perfect.

nopnop2002 commented 3 years ago

is parallel preferable over SPI?

It's case by case.

SPI is fast when drawing to consecutive addresses. The results for ColorBarTest and ColorTest represent this.

However, REGISTER I/O parallel is faster when drawing to non-contiguous addresses. This is useful when you use a lot of text. Because text fonts draw to almost non-contiguous addresses.

Performance comparison using ILI9341(240x320)

SPI used this.

Test SPI GPIO parallel REGISTER I/O parallel I2S parallel
FillTest 1620 2700 1920 1560
ColorBarTest 80 420 160 50
ArrowTest 250 460 170 140
LineTest 2690 1040 420 1530
CircleTest 2400 980 410 1370
RoundRectTest 2400 980 400 1390
RectAngleTest 5960 2010 940 6720
TriangleTest 6550 2120 990 7630
DirectionTest 420 520 200 240
HorizontalTest 990 720 300 580
VerticalTest 990 710 300 580
FillRectTest 160 730 300 120
ColorTest 240 850 330 190
BMPTest 1600 1930 1320 960
JPEGTest 2540 2940 2650 2530
PNGTest 2830 3210 2940 2810

The biggest advantage of using a parallel TFT is that there are clearly more types of devices than SPI.

marcdraco commented 3 years ago

Oh wow. Thank you so much! I can see what you mean - it literally is a case of picking the display that best suits the application.

Fonts really are a bind. I developed a couple of high performance variants of the Adafruit GFX routines for my last project and fonts are truly a cluster ... of pixels. That's one of the reasons I've moved from the ATMega328p from that project to the ESP32 for the current one (two actually).

Given that I'm sorely tempted to investigate customising the PCB to carry a full-sized parallel Arduino HAT. There's already a Streamdeck-like design with an TFT mounted in place but I haven't managed to get my hands on one yet to see if it will work for these projects which are aimed at schools.