hardware spi

Hardware SPI Support

Starting with version 2.2 of this code, in an effort to support additional OLED screens and bring new features, graphics support has migrated from the "default" Adafruit-GFX library to U8g2. Versions of the Digi-gurdy prior to this used a non-standard pin layout for the screen, and run their screen in "software" mode. This has proven too slow with the new graphical elements.

In order to support the on-board graphics card of the Teensy unit, the wiring to the screen must be altered on exiting Digi-Gurdies. v2.2+ requires it.

Units produced by John Dingley as of mid-December 2022 will come wired for "hardware" SPI as outlined below.

Pin Reassignments

Two of the wires going to the screen are ground and voltage-in. These do not need to be modified.

Your screen (especially if you source your own) may use the alternate names below instead of the more standard SPI names, particularly if the screen also supports I2C.

Name	Alternate Names	Old Pin Assignment	NEW Pin Assignment
CLK	SCK, SCL	10	13
MOSI	SDA, DATA	9	11
CS		12	10
DC		11	9
RESET	RST	13	38

Note: if your screen has an 8th pin called something like "3Vo", this is for voltage coming out of the screen. We don't use this at all. The Adafruit "white" screens are known to have this, for example.

Rewiring

John Dingley has produced a video which outlines what is required to re-wire an existing Digi-Gurdy. This process requires some light soldering (one new wire, one contact), and some short male-to-female jumper wires to rearrange the existing ones.

Caveats

• When using hardware SPI, pin 12 is unavailable. It is used by the SPI chip (for a function we do not use: input data from the screen). This is why RESET had to move to pin 38, an unused pin.
• It is possible to move the DC and RESET (and maybe CS) pins if you need to use a non-standard layout, but MOSI and CLK must be on pins 11 and 13. You would have to modify the code in display.h to refer to your layout if you do this.