See my Instructable for a full implementation example here.

All end stops, stepper driver fault lines, and buttons have their own external interrupt.

The Step pins of all four 8825 stepper drivers are PWM timer pins. As noted in the GitHub ReadMe file, PWM is used in one-shot mode to set the pulse width of the stepper pulse NOT the frequency of the pulses. This is because the step frequency is variable, it ramps up then down during a move. The one-shot pulse width offloads the pulse duration to hardware so that it results in a very accurate pulse width. The pulse width isn't important operationally, but it does make debugging the stepper pulses using a logic analyzer easier to interpret/verify. Note that the use of PWM is optional depending on what stepper library is used. I modified Lutz Niggl's TeensyStep library to work with the STM32F103 family of microprocessors. The modified TeensyStep library is included in my repository here.

The board contains a high-side switch and a digital potentiometer to control a motor speed controller. The high-side switch turns on the controller, and the potentiometer controls the speed. See my Instructable's BOM.txt for a link to a compatible speed controller here.

There is one connection for an optional servo.

The board uses a 12 pin FFC connector to connect a 480x320 display. The display can be the PCB shared here, or a generic display can be converted by using the FFC adapter shared here.