Enabling and disabling the TWIM instance

[hannes-hochreiner]

When a new TWIM instance is created, it is automatically enabled. This is very convenient in normal use. For a low power sensor, I found myself in the situation that I needed to deactivate (and later reactivate) the instance in order to safe energy. The simplest way I found to do this, was to add the "enable" and "disable" functions to the instance.

Please let me know, whether you would like to integrate this change into the main branch.

[Dirbaio]

+1 to this! I have done hacks with unsafe in my project to do this from outside the hal, having it in the hal would be very nice!

• Maybe there should be some safety against trying to do transfers while disabled?
• For more power saving, disconnect the sda/scl pins on disable (dir=input, input=disconnected), and connect them again on enable.

[jonas-schievink]

Thanks, this looks reasonable!