Modular low-level Playdate API

Low-level bindings to Playdate API with optional adapted official documentation and optional lang-items.

Main concepts in a thesis statement

1. We must panic when something wrong and we cannot recover from it. To give an example, when we hit null-ptr in api, thi is fatal.
2. We must return error when API returns error.

That looks pretty hardcore. That's why there is four+ possible ways to get access to API endpoints, among them returning Option or Result.

I've experimented enough with wrapping the entire API with results at every step, then painstakingly optimized their unfolding. And in the end I came to the conclusion that in this exact project the number of errors/results should be minimized.

What's inside

• cffi bindings
• pre-generated cffi bindings
• minimal required parts such as lang-items
• simple entry point
• additional utils like println macro

Prerequisites

1. Rust nightly toolchain (rustup is optional)
2. Playdate SDK
   • Ensure that env var PLAYDATE_SDK_PATH points to the SDK root
3. Follow the official documentation
   • Ensure that arm-none-eabi-gcc or gcc-arm-none-eabi in your PATH

Usage

[lib]
name = "example"
path = "src/lib.rs"
crate-type = [
	"dylib",     # for simulator
	"staticlib", # for hardware
]

[dependencies.pd]
package = "playdate-sys"
git = "this/repo/path.git"

#![no_std]
use core::ffi::*;

#[macro_use]
extern crate alloc;

#[macro_use]
extern crate pd;
use pd::ffi::*;


#[no_mangle]
// Note: `_arg` is a key-code in simulator, otherwise it's just zero.
pub extern "C" fn eventHandlerShim(api: *const PlaydateAPI, event: PDSystemEvent, _arg: u32) -> c_int {
	match event {
		PDSystemEvent::kEventInit => unsafe {
			// register the API entry point
			pd::API = api;
			// get `setUpdateCallback` fn
			let f = (*(*api).system).setUpdateCallback.unwrap();
			// register update callback
			f(Some(on_update), core::ptr::null_mut());

			// `println` uses `API` internally, that set above
			println!("Init, Hello world!");
		},

		PDSystemEvent::kEventLock => println!("Lock"),
		PDSystemEvent::kEventUnlock => println!("Unlock"),
		PDSystemEvent::kEventPause => println!("Pause"),
		PDSystemEvent::kEventResume => println!("Resume"),
		PDSystemEvent::kEventLowPower => println!("LowPower"),
		PDSystemEvent::kEventTerminate => println!("Terminate"),
		PDSystemEvent::kEventInitLua => println!("InitLua"),
		// simulator only, keyboard events:
		PDSystemEvent::kEventKeyPressed => println!("KeyPressed"),
		PDSystemEvent::kEventKeyReleased => println!("KeyReleased"),
	}

	0 // zero means "OK, no error, continue please"
}

unsafe extern "C" fn on_update(_: *mut c_void) -> i32 { 1 /* `1` means "OK, continue updates" */ }

[target.thumbv7em-none-eabihf]
rustflags = [
	"-Ctarget-cpu=cortex-m7",
	"-Clink-args=--emit-relocs",
	"-Crelocation-model=pic",
	"-Csoft-float=no",
	"-Clink-arg=--cref",
	"-Clink-arg=--gc-sections",
	"-Clink-arg=--entry=eventHandlerShim"
]

# Also I recommend to allow unstable options here:
[unstable]
unstable-options = true

cargo build --lib --release --target=thumbv7em-none-eabihf -Zbuild-std=core,alloc -Zunstable-options
# Note: on windows use gcc-arm-none-eabi instead
arm-none-eabi-gcc ./target/thumbv7em-none-eabihf/release/libexample.a \
			-nostartfiles -mthumb -mcpu=cortex-m7 -mfloat-abi=hard -mfpu=fpv5-sp-d16 -D__FPU_USED=1 \
			-Wl,--cref,--gc-sections,--no-warn-mismatch,--emit-relocs -mword-relocations \
			-fno-common -fno-exceptions \
			-T$PLAYDATE_SDK_PATH/C_API/buildsupport/link_map.ld \
			-o ./target/thumbv7em-none-eabihf/release/example.elf \
			--entry eventHandlerShim
# Then prepare package with manifest and assets, place into it example.elf and call
# `$PLAYDATE_SDK_PATH/bin/pdc` with path of prepared package.

See examples.

Configure profile

Little recommendation is to add this to your Cargo.toml

[profile.dev]
panic = "abort"

[profile.release]
panic = "abort"
opt-level = "s"         # optimize for binary size (or use `3`, play with it)
overflow-checks = false # runtime integer overflow checks. (optionally, as you wish)
lto = "fat"
incremental = false
codegen-units = 1

debug = 0
strip = "symbols"        # or debuginfo
debug-assertions = false

This is just recommendation because this is entirely optional including panic = "abort" for example (unwinding there is challenging but not impossible).

Configuration

There is some main kinds of features that you can control:

• bindgen-... controls binding generator and extra codegen features
• bindings-... to enable derives for types and some codegen like documentation
• lang-items and other hand-crafted things.

Control included parts

This crate contains some minimal required "parts" to build your application.

You can disable the features to prevent them from being and so you'll can use other allocator or panic-handler for example.

• allocator: global allocator
• panic-handler: global panic handler
• eh-personality: eh_personality for simulator-targets, dummy, empty, no-op

Non-default features:

• entry-point: simple minimal proxy entry point that caching API endpoint when app init.

Control bindings generation

By default if we have pregenerated bindings for your configuration (target, profile, derives, etc...) we use it instead of build new.

⚠️ Env var PLAYDATE_SDK_PATH have to points to the PlayDate SDK directory as described in official documentation.

To prevent this behavior to use only pre-built bindings set env var IGNORE_EXISTING_PLAYDATE_SDK=1.

There's bindgen used to generate bindings, and some features are re-exported:

• use bindgen-runtime to on/off bindgen uses runtime linking (dlopen) with libclang. Same for bindgen-static. More in bindgen docs.
• use features like bindings-derive-{name} to ask bindgen to derive {name} to all entities if it possible
  • full list of derive- features

    • bindings-derive-default
    • bindings-derive-eq
    • bindings-derive-copy
    • bindings-derive-debug
    • bindings-derive-hash
    • bindings-derive-ord
    • bindings-derive-partialeq
    • bindings-derive-partialord

Development

This crate should remain as low-level as possible.

It is possible to add extra things there only if that is:

• really small things
• absolutely necessary
• implementations of third-party traits (from other crates including core) for api types
• feature-gated, in case the thing has dependencies or isn't so small.

Extension Development

You can add functionality that based on this package. Just create a new your oun package on-top this and re-export all features.

I must repeat myself, I apologize for intruding.

⚠️ If you want to create a library that based on this library, please share following features of this package to allow everyone to properly configure entire dependency tree:

• bindgen-runtime
• bindgen-static

This makes kind of paramount importance if a user is using several of these extensions and it can be a mess if they dictate different configurations for this package.

• cargo new name-of-your-extension
• cargo add playdate-sys
• copy & paste all features mentioned above into your Cargo.toml like this:

  [features]
  default = ["playdate-sys/default"]
  bindgen-runtime = ["playdate-sys/bindgen-runtime"]
  bindgen-static = ["playdate-sys/bindgen-static"]
  bindings-derive-debug = ["playdate-sys/bindings-derive-debug"]
  

For example see existing crates in the repo/api.

How to generate prebuilt bindings?

This is full example how to generate bindings with doc-comments, but documentation is optional, so you can omit it - just remove all about docs:

• bindings-documentation feature
• execution playdate-docs-parser
• execution rustfmt

mk dir -p ./api/sys/gen

export PD_BUILD_PREBUILT=1

# all features excluding static- or runtime- linking bingen with libclang:
DERIVES_ALL=bindings-derive-default,bindings-derive-eq,bindings-derive-copy,bindings-derive-debug,bindings-derive-hash,bindings-derive-ord,bindings-derive-partialeq,bindings-derive-partialord
DERIVES_DEF=bindings-derive-debug

FEATURES_DEF=--features=bindings-documentation,$DERIVES_DEF
FEATURES_ALL=--features=bindings-documentation,$DERIVES_ALL

cargo build -p=playdate-sys $FEATURES_DEF
cargo build -p=playdate-sys $FEATURES_DEF --target=thumbv7em-none-eabihf

cargo build -p=playdate-sys $FEATURES_ALL
cargo build -p=playdate-sys $FEATURES_ALL --target=thumbv7em-none-eabihf

# optionally format bindings:
rustfmt ./api/sys/gen/*.rs

Important note: To trigger changing prebuilt bindings, you need set env var: PD_BUILD_PREBUILT, that allows changes outside of OUT_DIR.

This software is not sponsored or supported by Panic.