tagtagtag-ears

Linux driver for tagtagtag ears

Creates /dev/ear0 (left) and /dev/ear1 (right) to drive tagtagtag ears.

Installation

make
sudo make install

This adds:

dtoverlay=tagtagtag-ears

to /boot/config.txt

reboot

Usage

A single process can open /dev/ear0 (resp. /dev/ear1). Any further access will fail with EBUSY.

The following commands are accepted:

• '.' NOP
• '+' <count> Move ear steps forwards (count from 0 to 255)

Example:

echo -n -e '+\x03' > /dev/ear0

will move the ear 3 steps forward

• '-' <count> Move ear steps backwards (count from 0 to 255)

Example:

echo -n -e '-\x03' > /dev/ear0

will move the ear 3 steps backward

• '>' <position> Move ear forward until % 17 is reached. If position > 17, perform additional turns. If position is unknown, perform a detection running forward.

Example:

echo -n -e '>\x03' > /dev/ear0

will move the ear forward to position "3" (3 steps after missing hole).

• '<' <position> Move ear backward until % 17 is reached. If position > 17, perform additional turns. If position is unknown, perform a detection running backward.

Example:

echo -n -e '<\x03' > /dev/ear0

will move the ear forward to position "3" (3 steps after missing hole).

• '?' Get position or -1 if unknown (to be read from device)

Example:

echo -n -e '>\x03?' > /dev/ear0 && dd if=/dev/ear0 of=/dev/stdout count=1 bs=1

will output '\x03' after ear has been moved to position 3.

• '!' Get position, running a position detection if required.

Detecting user moves and blocking I/O

Detecting user moves is achieved by reading /dev/ear*. Read blocks until ear is moved (it will then return 'm') or a get position command is invoked. Once a 'm' is read, it will block until an additional movement occurs. Any command clears the buffer.

Writing will block if the ear is not idle. Most command will set the ear in a non-idle state, thus '.' can be used to block until the command ends. Compare:

 echo -n -e '+\x0A' > /dev/ear0

with:

 echo -n -e '+\x0A.' > /dev/ear0

The first line returns immediatly. The second line blocks until the ear moved the requested steps.

Broken ears

Ears are tested on start-up (ears perform a full turn which is also used to determine ear position). If, at any time, no rising GPIO interrupt is received within 3 seconds, the ear is considered broken. Any further write will fail. Reading will return EOF.