kernel: make user-kernel boundary in Chip

[bradjc]

Pull Request Overview

This pull request adds a new trait type to the Chip trait that represents the code that handles switching between kernelspace and userspace. Because this is a hardware feature, it makes sense to include it with the chip so that a user doesn't accidentally choose the wrong arch for a given MCU.

pub trait Chip {
    type MPU: mpu::MPU;
    type UserspaceKernelBoundary: syscall::UserspaceKernelBoundary;
    type SysTick: systick::SysTick;
    ...

This also simplifies main.rs as now setting up processes and the kernel only requires passing in the chip.

Testing Strategy

This pull request was tested by running a hail kernel.

TODO or Help Wanted

n/a

Documentation Updated

• Updated the relevant files in /docs, or no updates are required.

Formatting

• Ran make formatall.

[bradjc]

This should be rejected or merged before release testing (obviously I vote merged!).

[ppannuto]

From a skim of the changes, it's not immediately obvious why, but presumably after the rebase, something broke and this doesn't work for me. From minimal debugging, it looks like it hangs at the first syscall? (tested hail+blink, hail+c_hello)

[ppannuto]

Turns out this just needed to be rebased further to pick up the fix the from #1196.

Tested and working on hail+blink/c_hello/accel_leds. Looks good overall.

[alevy]

bors r+

[bors]

Build succeeded

• continuous-integration/travis-ci/push