This is the sixth post in a weekly series tracking the development of Tock, a safe multi-tasking operating system for microcontrollers.

HIL updates

Towards our goal releasing a stable enough version in early November to distribute, we’re working on revising the hardware interface layer (HIL) traits that glue chip-specific capsules (like a UART) with portable capsules (like a console).

@alevy posted a proposed revision of time related HIL traits—Alarm and Timer—to the mailing list. The Alarm trait lets a client set an alarm for a particular value of a wrapping counter. The Timer trait lets clients get a notification after a certain number of cycles has elapsed. We currently use Alarm for the TimerDriver (which acts like the Timer trait but for user space) as well as for virtualizing in the kernel since it is more accurate to virtualize.

@emosenkis proposed a a HIL trait for intrfacing with flash controllers.

@bradjc is working on extending the I2C HIL traits as part of his work on I2C slave support for the SAM4L (more details below).

I2C device driver

Until recently, Tock only had an implementation for the master side of the I2C interface. Our platform has a few I2C sensors, so that was the most important. The Signpost project, however, requires the SAM4L to be an I2C slave as well. @bradjc has been working on implementing both sides of the interface including pretty significant changes to the HIL to make this reasonably clean.