RP2040 I2C Refactor (ZigEmbeddedGroup#213)

* Various performance improvements to I2C reads/writes related to how/when polling occurs
* Simplified API so that all reading/writing happens in 3 functions
* Corrected tranlation of baud rate to register settings
* Tweaked how I2C is "initalized" and "deinitialized"
* Moved most of the error handling responsibility onto the caller of the I2C API, for example code no longer calls `panic()`, but rather bubbles up an error to the caller for them to make a decision on
* Added "const correctness" to API
* Added comments being explicit about what features of the hardware this API doesn't support
* Removed const correctness stuff
* Changed from_instance_number namespace
* Changed translate_baudrate namespace + moved tests
* Changed some terminology!
* Updated some function names and reverted some design patterns after further discussion
* Fixed example and changed how instances are accessed
* Removed redundant calls to get_regs()

---------

Co-authored-by: Hayden Riddiford <hayden@terrakaffe.com>

bsp/raspberrypi/rp2040/src/hal.zig

@@ -59,4 +59,5 @@ pub fn get_cpu_id() u32 {
 test "hal tests" {
     _ = pio;
     _ = usb;
+    _ = i2c;
 }

bsp/raspberrypi/rp2040/src/hal/adc.zig

@@ -109,8 +109,8 @@ pub const Input = enum(u3) {
         switch (in) {
             else => {
                 const pin = in.get_gpio_pin();
-                pin.set_function(.null);
-                pin.set_pull(null);
+                pin.set_function(.disabled);
+                pin.set_pull(.disabled);
                 pin.set_input_enabled(false);
             },
             .temp_sensor => {},

bsp/raspberrypi/rp2040/src/hal/gpio.zig

@@ -22,7 +22,7 @@ pub const Function = enum(u5) {
     pio1,
     gpck,
     usb,
-    null = 0x1f,
+    disabled = 0x1f,
 };
 
 pub const Direction = enum(u1) {
@@ -66,6 +66,7 @@ pub const Enabled = enum {
 pub const Pull = enum {
     up,
     down,
+    disabled,
 };
 
 pub fn num(n: u5) Pin {
@@ -99,7 +100,7 @@ pub const Mask = enum(u30) {
         }
     }
 
-    pub fn set_pull(self: Mask, pull: ?Pull) void {
+    pub fn set_pull(self: Mask, pull: Pull) void {
         const raw_mask = @intFromEnum(self);
         for (0..@bitSizeOf(Mask)) |i| {
             const bit = @as(u5, @intCast(i));
@@ -108,6 +109,24 @@ pub const Mask = enum(u30) {
         }
     }
 
+    pub fn set_slew_rate(self: Mask, slew_rate: SlewRate) void {
+        const raw_mask = @intFromEnum(self);
+        for (0..@bitSizeOf(Mask)) |i| {
+            const bit = @as(u5, @intCast(i));
+            if (0 != raw_mask & (@as(u32, 1) << bit))
+                num(bit).set_slew_rate(slew_rate);
+        }
+    }
+
+    pub fn set_schmitt_trigger(self: Mask, enabled: Enabled) void {
+        const raw_mask = @intFromEnum(self);
+        for (0..@bitSizeOf(Mask)) |i| {
+            const bit = @as(u5, @intCast(i));
+            if (0 != raw_mask & (@as(u32, 1) << bit))
+                num(bit).set_schmitt_trigger(enabled);
+        }
+    }
+
     pub fn put(self: Mask, value: u32) void {
         SIO.GPIO_OUT_XOR.raw = (SIO.GPIO_OUT.raw ^ value) & @intFromEnum(self);
     }
@@ -167,14 +186,12 @@ pub const Pin = enum(u5) {
         return @as(u32, 1) << @intFromEnum(gpio);
     }
 
-    pub inline fn set_pull(gpio: Pin, pull: ?Pull) void {
+    pub inline fn set_pull(gpio: Pin, pull: Pull) void {
         const pads_reg = gpio.get_pads_reg();
-
-        if (pull == null) {
-            pads_reg.modify(.{ .PUE = 0, .PDE = 0 });
-        } else switch (pull.?) {
+        switch (pull) {
             .up => pads_reg.modify(.{ .PUE = 1, .PDE = 0 }),
             .down => pads_reg.modify(.{ .PUE = 0, .PDE = 1 }),
+            .disabled => pads_reg.modify(.{ .PUE = 0, .PDE = 0 }),
         }
     }
 
@@ -231,4 +248,24 @@ pub const Pin = enum(u5) {
             .padding = 0,
         });
     }
+
+    pub fn set_slew_rate(gpio: Pin, slew_rate: SlewRate) void {
+        const pads_reg = gpio.get_pads_reg();
+        pads_reg.modify(.{
+            .SLEWFAST = switch (slew_rate) {
+                .slow => @as(u1, 0),
+                .fast => @as(u1, 1),
+            },
+        });
+    }
+
+    pub fn set_schmitt_trigger(gpio: Pin, enabled: Enabled) void {
+        const pads_reg = gpio.get_pads_reg();
+        pads_reg.modify(.{
+            .SCHMITT = switch (enabled) {
+                .enabled => @as(u1, 1),
+                .disabled => @as(u1, 0),
+            },
+        });
+    }
 };