add USB CDC support, and implement self-check diagnostic

firmware/Cargo.toml

@@ -14,14 +14,20 @@ ch32-hal = { git = "https://github.com/ju6ge/ch32-hal", branch = "feature/i2c-sl
 ], default-features = false }
 
 embassy-executor = { version = "0.7.0", features = [
-    "arch-riscv32",
+    # arch-riscv32's WFI-based sleep races with the USB interrupt wake signal,
+    # so tasks awaiting USB (e.g. wait_connection/write_packet) can hang
+    # forever even though the device enumerates fine. arch-spin busy-polls
+    # instead of sleeping, sidestepping the race. See CAN_Sensor/Cargo.toml
+    # for the same fix on the same ch32-hal/embassy-executor combo.
+    "arch-spin",
     "executor-thread",
 ] }
 
-embassy-time = { version = "0.4.0" }
-embassy-usb = { version = "0.3.0" }
+embassy-time = { version = "0.5.0", features = ["generic-queue-8"] }
+embassy-usb = { version = "0.5.1" }
 embassy-futures = { version = "0.1.0" }
 embassy-sync = { version = "0.7.2" }
+static_cell = "2.1.1"
 
 # This is okay because we should automatically use whatever ch32-hal uses
 qingke-rt = "*"
@@ -30,7 +36,7 @@ qingke = "*"
 panic-halt = "1.0"
 
 embedded-hal = "1.0.0"
-heapless = "0.8.0"
+heapless = { version = "0.8.0", features = ["portable-atomic-critical-section"] }
 micromath = { version = "2.1.0", features = ["num-traits"] }
 ch32-metapac = { version = "0.0.6", features = ["ch32v203c8t6"] }
 ina219 = "0.2.0"