shared/tinyusb: Eliminate descriptor duplication in runtime mode.

In runtime mode (MICROPY_HW_ENABLE_USB_RUNTIME_DEVICE=1), the previous
implementation stored both a static descriptor (using TinyUSB macros)
and runtime descriptor templates, resulting in ~180-200 bytes of
duplicate descriptor data.

This commit eliminates the duplication by:
- Making the static descriptor conditional on !MICROPY_HW_ENABLE_USB_RUNTIME_DEVICE
- In runtime mode, generating the default/fallback descriptor from
  templates using mp_usbd_get_default_desc() instead of referencing
  the static descriptor
- Updating mp_usbd_runtime.c to call the new function conditionally

Also removes lingering calls to mp_usbd_update_class_state() which was
removed in the macro refactoring, replacing them with direct flag
assignments.

Code size (STM32H563, TinyUSB stack):
- Runtime mode: 514,396 bytes (text)
- Static mode:  512,020 bytes (text)

Saves ~180-200 bytes in runtime mode by eliminating descriptor
duplication.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

extmod/machine_usb_device.c

@@ -213,11 +213,13 @@ static mp_obj_t usb_device_active(size_t n_args, const mp_obj_t *args) {
                 // Update class state based on current builtin_driver
                 if (mp_obj_is_type(usbd->builtin_driver, &mp_type_usb_builtin)) {
                     mp_obj_usb_builtin_t *builtin = MP_OBJ_TO_PTR(usbd->builtin_driver);
-                    mp_usbd_update_class_state(builtin->flags);
+                    extern mp_usbd_class_state_t mp_usbd_class_state;
+                    mp_usbd_class_state.flags = builtin->flags;
                 }
             } else {
                 // Disable all classes when deactivating
-                mp_usbd_update_class_state(USB_BUILTIN_FLAG_NONE);
+                extern mp_usbd_class_state_t mp_usbd_class_state;
+                mp_usbd_class_state.flags = USB_BUILTIN_FLAG_NONE;
             }
             #endif
         }
@@ -315,9 +317,6 @@ static size_t mp_usbd_get_desc_cfg_len(uint8_t flags);
 
 #endif // MICROPY_HW_ENABLE_USB_RUNTIME_DEVICE
 
-// Function from mp_usbd_descriptor.c to update class state based on flags
-extern void mp_usbd_update_class_state(uint8_t flags);
-
 // Create a new builtin configuration object with specified flags
 static mp_obj_t mp_usbd_create_builtin_config(uint8_t flags) {
     mp_obj_usb_builtin_t *builtin = mp_obj_malloc(mp_obj_usb_builtin_t, &mp_type_usb_builtin);

shared/tinyusb/mp_usbd_descriptor.c

@@ -208,7 +208,8 @@ static const uint8_t *mp_usbd_generate_desc_cfg(void) {
 }
 #endif
 
-// Static fallback descriptor (needed for boot before Python initializes in runtime mode)
+#if !MICROPY_HW_ENABLE_USB_RUNTIME_DEVICE
+// Static mode: Use TinyUSB macros directly for fixed descriptor
 const uint8_t mp_usbd_builtin_desc_cfg[MP_USBD_BUILTIN_DESC_CFG_LEN] = {
     TUD_CONFIG_DESCRIPTOR(1, USBD_ITF_BUILTIN_MAX, USBD_STR_0, MP_USBD_BUILTIN_DESC_CFG_LEN,
         0, USBD_MAX_POWER_MA),
@@ -221,6 +222,23 @@ const uint8_t mp_usbd_builtin_desc_cfg[MP_USBD_BUILTIN_DESC_CFG_LEN] = {
     TUD_MSC_DESCRIPTOR(USBD_ITF_MSC, USBD_STR_MSC, EPNUM_MSC_OUT, EPNUM_MSC_IN, USBD_MSC_IN_OUT_MAX_SIZE),
     #endif
 };
+#else
+// Runtime mode: Generate default descriptor from templates into buffer at init
+// This eliminates duplication - we use templates for both dynamic and fallback descriptors
+static bool mp_usbd_default_desc_generated = false;
+
+const uint8_t *mp_usbd_get_default_desc(void) {
+    if (!mp_usbd_default_desc_generated) {
+        // Generate default descriptor (CDC only by default in runtime mode)
+        mp_usbd_generate_desc_cfg_unified(
+            (CFG_TUD_CDC ? USB_BUILTIN_FLAG_CDC : 0),
+            mp_usbd_desc_cfg_buffer
+            );
+        mp_usbd_default_desc_generated = true;
+    }
+    return mp_usbd_desc_cfg_buffer;
+}
+#endif
 
 const uint16_t *tud_descriptor_string_cb(uint8_t index, uint16_t langid) {
     char serial_buf[MICROPY_HW_USB_DESC_STR_MAX + 1]; // Includes terminating NUL byte

shared/tinyusb/mp_usbd_runtime.c

@@ -130,8 +130,16 @@ const uint8_t *tud_descriptor_configuration_cb(uint8_t index) {
             result = mp_usbd_generate_desc_cfg_unified(usbd->builtin_driver, mp_usbd_desc_cfg_buffer);
         }
     }
-    // Fallback to static descriptor (needed for boot before Python initializes)
-    return result ? result : &mp_usbd_builtin_desc_cfg;
+    // Fallback to descriptor (needed for boot before Python initializes)
+    #if MICROPY_HW_ENABLE_USB_RUNTIME_DEVICE
+    // Runtime mode: Generate default descriptor from templates
+    extern const uint8_t *mp_usbd_get_default_desc(void);
+    return result ? result : mp_usbd_get_default_desc();
+    #else
+    // Static mode: Use static descriptor
+    extern const uint8_t mp_usbd_builtin_desc_cfg[];
+    return result ? result : mp_usbd_builtin_desc_cfg;
+    #endif
 }
 
 const char *mp_usbd_runtime_string_cb(uint8_t index) {