In order to avoid having to set the time every time I switch my Gameboy on, I wanted to make use of an RTC clock.

Certain expensives flash cartridges do have an embedded RTC but mine hasn't. So I decided to add a RTC feature through the link port.

ArduinoBoy is an existing project that allows you to control by sending MIDI instructions through the link port, it happens to support the Teensy 3, which is quite nice because the Teensy3 has an embedded RTC, so no need to add an external component, just an external battery. Or at least that what I thought, because when I read carefully the Teensy 3.1 spec, it requires an oscillator, unlike the 3.5 and 3.6.

I struggled a bit to get the link port to work. I wanted to use other ports that those used by ArduinoBoy, but I hadn't noticed that ArduinoBoy access the pins through port commands, and not digitalWrite()!

So, currently my Teensy code works with the GBDK Comm example, but I'll wait to have receive the oscillator to make modifications on my alarm_clock GB code.

The schematic is quite simple :

The implementation is a bit more messy ;-)

At first I tried to do a home made link connector but as I was debugging my Teensy software, I wanted a reliable hardware to only fix one bug at a time, so I ended up using an old gba cable connector.

My plan is to do some more soldering and fit everything in a Mario candy box