QUESTION: SPI or parallel for new designs?

[marcdraco]

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]

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]

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.