From 886234b88284bd90c951b930c98f28681140435b Mon Sep 17 00:00:00 2001
From: Matt Knight <mattnite@proton.me>
Date: Mon, 15 May 2023 23:12:22 -0700
Subject: [PATCH] improve timer API (#60)

---
 examples/usb_device.zig |  4 ++--
 examples/usb_hid.zig    |  4 ++--
 src/hal/time.zig        | 35 +++++++++++++++++------------------
 src/hal/uart.zig        |  4 ++--
 4 files changed, 23 insertions(+), 24 deletions(-)

diff --git a/examples/usb_device.zig b/examples/usb_device.zig
index 3395286..252db52 100644
--- a/examples/usb_device.zig
+++ b/examples/usb_device.zig
@@ -154,7 +154,7 @@ pub fn main() !void {
     rp2040.usb.Usb.init_clk();
     // Then initialize the USB device using the configuration defined above
     rp2040.usb.Usb.init_device(&DEVICE_CONFIGURATION) catch unreachable;
-    var old: u64 = time.get_time_since_boot().us_since_boot;
+    var old: u64 = time.get_time_since_boot().to_us();
     var new: u64 = 0;
     while (true) {
         // You can now poll for USB events
@@ -162,7 +162,7 @@ pub fn main() !void {
             false, // debug output over UART [Y/n]
         ) catch unreachable;
 
-        new = time.get_time_since_boot().us_since_boot;
+        new = time.get_time_since_boot().to_us();
         if (new - old > 500000) {
             old = new;
             led.toggle();
diff --git a/examples/usb_hid.zig b/examples/usb_hid.zig
index 051ad74..a19a3e0 100644
--- a/examples/usb_hid.zig
+++ b/examples/usb_hid.zig
@@ -169,7 +169,7 @@ pub fn main() !void {
     rp2040.usb.Usb.init_clk();
     // Then initialize the USB device using the configuration defined above
     rp2040.usb.Usb.init_device(&DEVICE_CONFIGURATION) catch unreachable;
-    var old: u64 = time.get_time_since_boot().us_since_boot;
+    var old: u64 = time.get_time_since_boot().to_us();
     var new: u64 = 0;
     while (true) {
         // You can now poll for USB events
@@ -177,7 +177,7 @@ pub fn main() !void {
             true, // debug output over UART [Y/n]
         ) catch unreachable;
 
-        new = time.get_time_since_boot().us_since_boot;
+        new = time.get_time_since_boot().to_us();
         if (new - old > 500000) {
             old = new;
             led.toggle();
diff --git a/src/hal/time.zig b/src/hal/time.zig
index 3b568bf..d7f815b 100644
--- a/src/hal/time.zig
+++ b/src/hal/time.zig
@@ -1,8 +1,19 @@
 const microzig = @import("microzig");
 const TIMER = microzig.chip.peripherals.TIMER;
 
-pub const Absolute = struct {
-    us_since_boot: u64,
+/// Using an enum to make it a distinct type, the underlying number is
+/// time since boot in microseconds.
+pub const Absolute = enum(u64) {
+    _,
+
+    pub fn reached(time: Absolute) bool {
+        const now = get_time_since_boot();
+        return now.to_us() >= time.to_us();
+    }
+
+    pub fn to_us(time: Absolute) u64 {
+        return @enumToInt(time);
+    }
 };
 
 pub fn get_time_since_boot() Absolute {
@@ -12,23 +23,14 @@ pub fn get_time_since_boot() Absolute {
         var low_word = TIMER.TIMERAWL;
         const next_high_word = TIMER.TIMERAWH;
         if (next_high_word == high_word)
-            break Absolute{
-                .us_since_boot = @intCast(u64, high_word) << 32 | low_word,
-            };
+            break @intToEnum(Absolute, @intCast(u64, high_word) << 32 | low_word);
 
         high_word = next_high_word;
     } else unreachable;
 }
 
 pub fn make_timeout_us(timeout_us: u64) Absolute {
-    return Absolute{
-        .us_since_boot = get_time_since_boot().us_since_boot + timeout_us,
-    };
-}
-
-pub fn reached(time: Absolute) bool {
-    const now = get_time_since_boot();
-    return now.us_since_boot >= time.us_since_boot;
+    return @intToEnum(Absolute, get_time_since_boot().to_us() + timeout_us);
 }
 
 pub fn sleep_ms(time_ms: u32) void {
@@ -36,9 +38,6 @@ pub fn sleep_ms(time_ms: u32) void {
 }
 
 pub fn sleep_us(time_us: u64) void {
-    const end_time = Absolute{
-        .us_since_boot = time_us + get_time_since_boot().us_since_boot,
-    };
-
-    while (!reached(end_time)) {}
+    const end_time = make_timeout_us(time_us);
+    while (!end_time.reached()) {}
 }
diff --git a/src/hal/uart.zig b/src/hal/uart.zig
index 6a08b85..b7a9b11 100644
--- a/src/hal/uart.zig
+++ b/src/hal/uart.zig
@@ -219,8 +219,8 @@ pub fn log(
 
     if (uart_logger) |uart| {
         const current_time = time.get_time_since_boot();
-        const seconds = current_time.us_since_boot / std.time.us_per_s;
-        const microseconds = current_time.us_since_boot % std.time.us_per_s;
+        const seconds = current_time.to_us() / std.time.us_per_s;
+        const microseconds = current_time.to_us() % std.time.us_per_s;
 
         uart.print(prefix ++ format ++ "\r\n", .{ seconds, microseconds } ++ args) catch {};
     }