Add BSP features for usb-logging and systick #65
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Each feature is enabled by default (since we're trying to maintain backwards compatibility, for now). By disabling the "usb-logging" feature, we don't have to depend on the teensy4-usb-sys, so that becomes an optional dependency.
This is a breaking change. It closes #36. Since there's a "systick" feature, we can more readily isolate the SYSTICK code behind a conditionally-compiled systick module. We expose a SysTick timer struct with a simple delay() method to provide the same functionality. The new struct implements the blocking delay trait of the embedded-hal. Tested with 'make download_systick' and observing a blinking LED. All examples build.
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CC @mitchmindtree. Let me know if we'd rather keep this on the back-burner until we merge in RTIC support. |
| @@ -227,6 +236,9 @@ pub struct Peripherals { | |||
| pub gpt2: hal::gpt::Unclocked, | |||
| /// DMA channels | |||
| pub dma: hal::dma::Unclocked, | |||
| /// The SysTick delay timer | |||
| #[cfg(feature = "systick")] | |||
| pub systick: SysTick, | |||
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Having feature-gated fields on structs can break stuff when adding their associated features due to rust's exhaustive pattern matching - I think this is normally avoided by keeping the fields private to disallow exhaustively matching on the struct and exposing them via methods instead. In our case however I think this is probably totally fine, especially as exposing only some peripherals via methods would inevitably lead to ownership issues that would be much more annoying to deal with heh!
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Great call. It sounds like we need to prevent exhaustive pattern matching, and a #[non_exhaustive] attribute on Peripherals might be perfect for that. That should let users enable features without introducing compilation errors.
Users who were using features, but want to disable features, would still need to guard against these members disappearing, just as they would have to deal with conditionally-compiled methods disappearing.
We don't need the log crate if we're not using usb-logging
This should force users who are *not* using default features safely pattern-match against the `Peripherals` struct.
See the discussions on #64. This PR adds two, default features for the
teensy4-bsp:"usb-logging"enables the USB logging capabilities. Depends on"systick"."systick"enables the BSP's definition of the SYSTICK exception handler.The goal is to keep features additive, as expected by cargo. At the same time, we keep the two features enabled by default for backwards compatibility.
#64 proposes that we add RTIC support behind a new feature,
"rtic". If this is accepted, users will have to disable default features before safely enabling the"rtic"feature.This also knocks-out #36, since we were messing with SYSTICK.