Here's a driver for the MTDS module. It implements only a small subset of the C++ MTDS driver's functionalities, but it's a representative subset: I think any other desired feature could be implemented by finding where the C++ driver constructs the relevant payloads and copy-pasting the routines I've written with the protocol constants changed. Functionality which is covered includes relaying touch events to interested Erlang-side applications, drawing lines, printing text, setting color options, and double-buffering (although I did not test this last one).

I also included two demos:

1. mtds_hello: Writes "Hello, World!" in green text at the top-left corner of the screen. Based off of MtdsDemo1.pde:MtdsTest21.
2. mtds_sketch: An Erlang server which listens for touch events and converts them into draw events, so you can draw on the screen with your finger.

Sample run of the two included demos:

1> pmod_mtds:start_link(spi2).
{ok,<0.314.0>}
2> mtds_sketch:start_link().
{ok,<0.317.0>}
% scribbled 'GRiSP' with my finger
3> gen_server:stop(pid(0,317,0)).
ok
% needed to release the display handle
4> mtds_hello:run().
ok
% printed 'Hello, World!' in green text in the corner
5> mtds_sketch:start_link().
{ok,<0.321.0>}
% back to scribbling

NOTE: I used OTP 27's -doc directives. I'm happy to change them to edoc comments if that's unacceptable — though it will take me a minute, since I've never used edoc comments before.