Cycle accurate implementation

Makefile

@@ -0,0 +1,20 @@
+# Makefile useful during development.
+# `make asm` compiles examples/codegen.rs to assembly.
+# The output can then be reviewed for correctness.
+
+NV?=nightly
+override FLAGS += -Z build-std=core -Z build-std-features=panic_immediate_abort --release
+MCU?=avr-atmega328p
+AVR_CPU_FREQUENCY_HZ?=16000000
+export AVR_CPU_FREQUENCY_HZ
+
+build:
+	cargo +$(NV) build $(FLAGS) --target=$(MCU).json -v
+	cargo +$(NV) build --example codegen $(FLAGS) --target=$(MCU).json -v
+
+asm:
+	cargo +$(NV) rustc --example codegen $(FLAGS) --target=$(MCU).json -- --emit asm
+	@echo target/$(MCU)/release/examples/*.s
+
+asmclean:
+	-rm target/*/release/deps/*.s

README.md

@@ -5,36 +5,35 @@
 
 [API Documentation](https://docs.rs/avr_delay/)
 
-The intent of this library is to provide avr specific delay routines similar to the ones provided by the arduino library. The public functions are:
+The intent of this library is to provide avr specific delay routines similar to the ones provided by the arduino library.
 
 ## `$AVR_CPU_FREQUENCY_HZ`
 
 This crate uses the [`avr-config`](https://crates.io/crates/avr-config) crate for fetching the CPU frequency. As such, the `AVR_CPU_FREQUENCY_HZ` environment variable will need to be set when compiling your crate for AVR.
 
-Example:
-
 ```bash
 export AVR_CPU_FREQUENCY_HZ=16000000
 cargo build -Z build-std=core --target avr-atmega328p.json --release
 ```
 
-```rust
-delay(count: u32)
-```
-
-is a raw delay loop. Each loop is 4 cycles. The asm section can loop 65536 times. Initial overhead is about 13 cycles. Each outer loop has an overhead of about 11 cycles.
+## API
 
 ```rust
-delay_us(us: u32)
+delay_cycles<const CYCLES: u64>()
+delay_us<const US: u64>()
+delay_ms<const MS: u64>()
+delay_sec<const SEC: u64>()
 ```
 
-delay _us_ microseconds
+`delay_cycles` accepts 0 to 25_769_803_784 cycles (almost 18 minutes at 24Mhz).
+
+The other functions convert time to cycles by using CPU_FREQUENCY_HZ.
 
 ```rust
-delay_ms(ms: u32)
+delay_ms<42>(); // delay by 42ms (exactly 1_008_000 cycles at 24Mhz).
 ```
 
-delay _ms_ milliseconds
+## Example
 
 A simple example of how to use it follows.
 
@@ -64,7 +63,7 @@ extern crate avr_delay;
 
 use arduino::{DDRB, PORTB};
 use core::ptr::write_volatile;
-use avr_delay::{delay, delay_ms, delay_us};
+use avr_delay::delay_ms;
 
 #[no_mangle]
 pub extern fn main() {
@@ -73,7 +72,7 @@ pub extern fn main() {
     loop {
         out = out ^ 0xff;
         unsafe { write_volatile(PORTB, out) }
-        delay_ms(1000000);
+        delay_ms<1000000>();
     }
 }
 

examples/codegen.rs

@@ -0,0 +1,143 @@
+#![no_std]
+#![no_main]
+
+extern crate avr_std_stub;
+
+use avr_delay::delay_cycles;
+
+#[no_mangle]
+fn main() {}
+
+/*
+
+Interesting corner case values. They are picked to be right around the switch between lower to
+higher number of bits for the dealy counter.
+
+#!/bin/bash
+while read i; do
+    echo "#[inline(never)] #[no_mangle] pub fn test_${i}() { delay_cycles::<${i}>(); }"
+done <<EOF
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+11
+12
+767
+768
+769
+770
+771
+772
+773
+774
+262_144
+262_145
+262_146
+262_147
+262_148
+262_149
+262_150
+262_151
+262_152
+262_153
+262_154
+262_155
+83_886_081
+83_886_082
+83_886_083
+83_886_084
+83_886_085
+83_886_086
+83_886_087
+83_886_088
+83_886_089
+83_886_090
+83_886_091
+83_886_092
+83_886_093
+83_886_094
+83_886_095
+25_769_803_778
+25_769_803_779
+25_769_803_780
+25_769_803_783
+25_769_803_784
+EOF
+
+*/
+
+#[inline(never)] #[no_mangle] pub fn test_0() { delay_cycles::<0>(); }
+#[inline(never)] #[no_mangle] pub fn test_1() { delay_cycles::<1>(); }
+#[inline(never)] #[no_mangle] pub fn test_2() { delay_cycles::<2>(); }
+#[inline(never)] #[no_mangle] pub fn test_3() { delay_cycles::<3>(); }
+#[inline(never)] #[no_mangle] pub fn test_4() { delay_cycles::<4>(); }
+#[inline(never)] #[no_mangle] pub fn test_5() { delay_cycles::<5>(); }
+#[inline(never)] #[no_mangle] pub fn test_6() { delay_cycles::<6>(); }
+#[inline(never)] #[no_mangle] pub fn test_7() { delay_cycles::<7>(); }
+#[inline(never)] #[no_mangle] pub fn test_8() { delay_cycles::<8>(); }
+#[inline(never)] #[no_mangle] pub fn test_9() { delay_cycles::<9>(); }
+#[inline(never)] #[no_mangle] pub fn test_11() { delay_cycles::<11>(); }
+#[inline(never)] #[no_mangle] pub fn test_12() { delay_cycles::<12>(); }
+#[inline(never)] #[no_mangle] pub fn test_767() { delay_cycles::<767>(); }
+#[inline(never)] #[no_mangle] pub fn test_768() { delay_cycles::<768>(); }
+#[inline(never)] #[no_mangle] pub fn test_769() { delay_cycles::<769>(); }
+#[inline(never)] #[no_mangle] pub fn test_770() { delay_cycles::<770>(); }
+#[inline(never)] #[no_mangle] pub fn test_771() { delay_cycles::<771>(); }
+#[inline(never)] #[no_mangle] pub fn test_772() { delay_cycles::<772>(); }
+#[inline(never)] #[no_mangle] pub fn test_773() { delay_cycles::<773>(); }
+#[inline(never)] #[no_mangle] pub fn test_774() { delay_cycles::<774>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_144() { delay_cycles::<262_144>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_145() { delay_cycles::<262_145>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_146() { delay_cycles::<262_146>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_147() { delay_cycles::<262_147>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_148() { delay_cycles::<262_148>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_149() { delay_cycles::<262_149>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_150() { delay_cycles::<262_150>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_151() { delay_cycles::<262_151>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_152() { delay_cycles::<262_152>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_153() { delay_cycles::<262_153>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_154() { delay_cycles::<262_154>(); }
+#[inline(never)] #[no_mangle] pub fn test_262_155() { delay_cycles::<262_155>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_081() { delay_cycles::<83_886_081>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_082() { delay_cycles::<83_886_082>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_083() { delay_cycles::<83_886_083>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_084() { delay_cycles::<83_886_084>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_085() { delay_cycles::<83_886_085>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_086() { delay_cycles::<83_886_086>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_087() { delay_cycles::<83_886_087>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_088() { delay_cycles::<83_886_088>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_089() { delay_cycles::<83_886_089>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_090() { delay_cycles::<83_886_090>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_091() { delay_cycles::<83_886_091>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_092() { delay_cycles::<83_886_092>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_093() { delay_cycles::<83_886_093>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_094() { delay_cycles::<83_886_094>(); }
+#[inline(never)] #[no_mangle] pub fn test_83_886_095() { delay_cycles::<83_886_095>(); }
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_778() { delay_cycles::<25_769_803_778>(); }
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_779() { delay_cycles::<25_769_803_779>(); }
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_780() { delay_cycles::<25_769_803_780>(); }
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_783() { delay_cycles::<25_769_803_783>(); }
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_784() { delay_cycles::<25_769_803_784>(); }
+
+// This shouldn't compile, but we don't have static assertion yet. The code produced is still
+// correct. But it costs more than calling delay_cycles twice.
+#[inline(never)] #[no_mangle] pub fn test_25_769_803_785_bad() { delay_cycles::<25_769_803_785>(); }
+
+// This shouldn't compile, but we don't have static assertion yet. The code produced is still
+// correct. But it costs more than calling delay_cycles twice.
+#[inline(never)] #[no_mangle] pub fn test_25_853_952_778_bad() { delay_cycles::<25_853_952_778>(); }
+
+// This shouldn't compile, but we don't have static assertion yet. The code produced is still
+// correct. But it costs more than calling delay_cycles twice. This is the absolute limit.
+#[inline(never)] #[no_mangle] pub fn test_25_853_952_779_bad() { delay_cycles::<25_853_952_779>(); }
+
+// This shouldn't compile, but we don't have static assertion yet. This does overflow and should
+// produces the same function as 25_769_803_778.
+#[inline(never)] #[no_mangle] pub fn test_25_853_952_780_overflow() { delay_cycles::<25_853_952_780>(); }

examples/milliseconds.rs

@@ -5,5 +5,5 @@ extern crate avr_std_stub;
 
 #[no_mangle]
 fn main() {
-    avr_delay::delay_ms(4500);
+    avr_delay::delay_ms::<4500>();
 }