## Background/motivation
The Nintendo 3DS is supported by the tier 3 rust target
[armv6k-nintendo-3ds](https://doc.rust-lang.org/rustc/platform-support/armv6k-nintendo-3ds.html#armv6k-nintendo-3ds).
Bevy does not officially support the device, but as more of bevy becomes
`no_std` compatible, more targets are being partially supported (e.g.
GBA - https://github.com/bevyengine/bevy/discussions/10680,
https://github.com/bushrat011899/bevy_mod_gba) officially or not.
The Nintendo 3DS runs Horizon as its OS which is
[unix-based](4d08223c05/compiler/rustc_target/src/spec/targets/armv6k_nintendo_3ds.rs (L34)),
and the above target (at least partially) supports rust std. It makes
sense that you would want to use it, since the 3DS supports things like
filesystem reads and the system clock.
## Problem
Unlike standard unix targets, armv6k-nintendo-3ds is not one that can
use/build the the `ctrlc` dependency in `bevy_app` which is enabled by
the bevy `std` cargo feature.
Without the `std` feature flag, scheduled systems panic without
providing another way for bevy to tick using the `Instant` type (like
you might for a
[GBA](72d8bbf47b/src/time.rs (L36))).
<details>
<summary>Example</summary>
```
Finished `dev` profile [optimized + debuginfo] target(s) in 1m 39s
Building smdh: /home/maya/repos/hyperspace-dj/target/armv6k-nintendo-3ds/debug/hyperspace-dj.smdh
Building 3dsx: /home/maya/repos/hyperspace-dj/target/armv6k-nintendo-3ds/debug/hyperspace-dj.3dsx
Adding RomFS from /home/maya/repos/hyperspace-dj/romfs
Running 3dslink
Sending hyperspace-dj.3dsx, 7172344 bytes
2777346 sent (38.72%), 233 blocks
starting server
server active ...
hii we'are about the to start the bevy app
thread 'main' panicked at /home/maya/repos/bevy/crates/bevy_platform/src/time/fallback.rs:177:13:
An elapsed time getter has not been provided to `Instant`. Please use `Instant::set_elapsed(...)` before calling `Instant::now()`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```
</details>
## Solution
This PR simply excludes the `ctrlc` dependency and its uses in
`bevy_app` for the 3DS target (`horizon`) with an addition to its
existing feature flags.
After this fix, we can use the `std` feature, and regular scheduled
systems no longer panic because of missing `Instant` (system clock)
support.
## Testing
I compiled and ran a binary with the modified version of bevy, using
`no_default_features` and feature flags `default_no_std` and `std` on a
physical 3DS (classic) using homebrew and `cargo-3ds`.
Toolchain:
[armv6k-nintendo-3ds](https://doc.rust-lang.org/rustc/platform-support/armv6k-nintendo-3ds.html#armv6k-nintendo-3ds)
(nightly-2025-03-31)
Project reference:
440fc10184
## Considerations
It could be that we don't want to add specific exceptions inside bevy to
support specific hardware with weird quirks inside general bevy code,
but it's not obvious to me what we should use instead of an exception to
(pre-existing) target cfg: every change here is merely an addition to a
cfg that already checks for both the target family and the `std` flag.
It is not clear to me if this PR is exhaustive enough to be considered
an adequate solution for the larger goal of partially supporting the
3DS, but it seems to be a step in the right direction because it at
least lets trivial App::run setups with scheduled systems work.
f93e5c5622