feat(f722): add usb mavlink transport

firmware/libs/kaptan-mavlink/src/receiver.rs

@@ -5,7 +5,7 @@ use crate::{MavlinkFrame, decode_message, generated::kaptan::MavMessage};
 /// An unsigned MAVLink 2 frame whose ID and CRC match the Kaptan dialect.
 ///
 /// The payload is deliberately not decoded during byte admission. Consumers
-/// decode it once after taking the frame from the bounded receive queue.
+/// decode it once at protocol dispatch.
 #[repr(transparent)]
 pub struct IntegrityCheckedFrame(MavlinkFrame);
 
@@ -32,14 +32,20 @@ impl IntegrityCheckedFrame {
     }
 }
 
-struct IntegrityFramer {
+/// Incremental, unbuffered MAVLink 2 framing with Kaptan ID and CRC validation.
+///
+/// Consumers that can pause byte admission can process each returned frame
+/// directly. Interrupt-driven byte streams can use [`IntegrityMavlinkReceiver`]
+/// to queue complete frames instead. Accepted frames remain unauthenticated.
+pub struct IntegrityMavlinkFramer {
     frame: MavlinkFrame,
     received: usize,
     expected: usize,
 }
 
-impl IntegrityFramer {
-    const fn new() -> Self {
+impl IntegrityMavlinkFramer {
+    /// Creates an empty framer.
+    pub const fn new() -> Self {
         Self {
             frame: MavlinkFrame::new(),
             received: 0,
@@ -47,7 +53,8 @@ impl IntegrityFramer {
         }
     }
 
-    fn receive_byte(&mut self, byte: u8) -> Option<IntegrityCheckedFrame> {
+    /// Consumes one byte, returning a complete integrity-checked frame if ready.
+    pub fn receive_byte(&mut self, byte: u8) -> Option<IntegrityCheckedFrame> {
         if self.received == 0 {
             if byte == 0xfd {
                 self.frame.as_mut_slice()[0] = byte;
@@ -81,20 +88,27 @@ impl IntegrityFramer {
         IntegrityCheckedFrame::try_new(frame)
     }
 
-    fn reset(&mut self) {
+    /// Discards a partial frame after a stream discontinuity.
+    pub fn reset(&mut self) {
         self.frame = MavlinkFrame::new();
         self.received = 0;
         self.expected = 0;
     }
 }
 
+impl Default for IntegrityMavlinkFramer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Bounded integrity-only MAVLink 2 receiver.
 ///
 /// It rejects signed, incompatible, corrupt, and MAVLink 1 frames, but an
 /// accepted frame is still unauthenticated. The composition decides whether
 /// and how a received request may be admitted.
 pub struct IntegrityMavlinkReceiver<const N: usize> {
-    framer: IntegrityFramer,
+    framer: IntegrityMavlinkFramer,
     frames: [Option<IntegrityCheckedFrame>; N],
     front: usize,
     length: usize,
@@ -105,7 +119,7 @@ impl<const N: usize> IntegrityMavlinkReceiver<N> {
     pub const fn new() -> Self {
         assert!(N != 0, "integrity receiver capacity must be nonzero");
         Self {
-            framer: IntegrityFramer::new(),
+            framer: IntegrityMavlinkFramer::new(),
             frames: [const { None }; N],
             front: 0,
             length: 0,