Save 25 to 50 bytes of flash by storing "CircuitPython" once in the USB names

shared-module/usb_audio/__init__.c

@@ -329,7 +329,7 @@ size_t usb_audio_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *de
         const uint8_t ep_out = forced_iso_ep ? iso_ep_num : descriptor_counts->current_endpoint;
         const uint8_t ep_in = forced_iso_ep ? iso_ep_num : (descriptor_counts->current_endpoint + 1);
 
-        usb_add_interface_string(*current_interface_string, "CircuitPython Headset");
+        usb_add_interface_name(*current_interface_string, NULL, "Headset");
 
         const uint8_t usb_audio_descriptor[] = {
             USB_AUDIO_HEADSET_DESCRIPTOR(
@@ -365,7 +365,7 @@ size_t usb_audio_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *de
     }
 
     if (usb_audio_direction_is_output()) {
-        usb_add_interface_string(*current_interface_string, "CircuitPython Speaker");
+        usb_add_interface_name(*current_interface_string, NULL, "Speaker");
 
         // The AudioStreaming interface follows the AudioControl interface.
         usb_audio_spk_as_itf = descriptor_counts->current_interface + 1;
@@ -394,7 +394,7 @@ size_t usb_audio_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *de
         return sizeof(usb_audio_descriptor);
     }
 
-    usb_add_interface_string(*current_interface_string, "CircuitPython Microphone");
+    usb_add_interface_name(*current_interface_string, NULL, "Microphone");
 
     // The AudioStreaming interface follows the AudioControl interface.
     usb_audio_mic_as_itf = descriptor_counts->current_interface + 1;

shared-module/usb_cdc/__init__.c

@@ -126,10 +126,10 @@ static const uint8_t usb_cdc_descriptor_template[] = {
     0x00,        // 65 bInterval 0 (unit depends on device speed)
 };
 
-static const char console_cdc_comm_interface_name[] = USB_INTERFACE_NAME " CDC control";
-static const char data_cdc_comm_interface_name[] = USB_INTERFACE_NAME " CDC2 control";
-static const char console_cdc_data_interface_name[] = USB_INTERFACE_NAME " CDC data";
-static const char data_cdc_data_interface_name[] = USB_INTERFACE_NAME " CDC2 data";
+static const char console_cdc_comm_interface_name[] = "CDC control";
+static const char data_cdc_comm_interface_name[] = "CDC2 control";
+static const char console_cdc_data_interface_name[] = "CDC data";
+static const char data_cdc_data_interface_name[] = "CDC2 data";
 
 // .idx is set later.
 
@@ -205,41 +205,24 @@ size_t usb_cdc_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *desc
     descriptor_counts->current_endpoint++;
 
     #if CIRCUITPY_FULL_BUILD
-    const char *control_interface_name =
-        console ? console_cdc_comm_interface_name : data_cdc_comm_interface_name;
-    const char *data_interface_name =
-        console ? console_cdc_data_interface_name : data_cdc_data_interface_name;
-
-    char *custom_control_interface_name =
+    const char *custom_control_interface_name =
         console ? custom_usb_cdc_console_control_interface_name : custom_usb_cdc_data_control_interface_name;
-    char *custom_data_interface_name =
+    const char *custom_data_interface_name =
         console ? custom_usb_cdc_console_data_interface_name : custom_usb_cdc_data_data_interface_name;
-
-    if (custom_control_interface_name != NULL) {
-        control_interface_name = custom_control_interface_name;
-    }
-    if (custom_data_interface_name != NULL) {
-        data_interface_name = custom_data_interface_name;
-    }
-
-    usb_add_interface_string(*current_interface_string, control_interface_name);
-    descriptor_buf[CDC_COMM_INTERFACE_STRING_INDEX] = *current_interface_string;
-    (*current_interface_string)++;
-
-    usb_add_interface_string(*current_interface_string, data_interface_name);
-    descriptor_buf[CDC_DATA_INTERFACE_STRING_INDEX] = *current_interface_string;
-    (*current_interface_string)++;
     #else
-    usb_add_interface_string(*current_interface_string,
+    const char *custom_control_interface_name = NULL;
+    const char *custom_data_interface_name = NULL;
+    #endif
+
+    usb_add_interface_name(*current_interface_string, custom_control_interface_name,
         console ? console_cdc_comm_interface_name : data_cdc_comm_interface_name);
     descriptor_buf[CDC_COMM_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 
-    usb_add_interface_string(*current_interface_string,
+    usb_add_interface_name(*current_interface_string, custom_data_interface_name,
         console ? console_cdc_data_interface_name : data_cdc_data_interface_name);
     descriptor_buf[CDC_DATA_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
-    #endif
 
     return sizeof(usb_cdc_descriptor_template);
 }
@@ -370,7 +353,7 @@ static const uint8_t usb_vendor_descriptor_template[] = {
     0x0          // 22  bInterval 0
 };
 
-static const char vendor_interface_name[] = USB_INTERFACE_NAME " WebUSB";
+static const char vendor_interface_name[] = "WebUSB";
 
 
 bool usb_vendor_enabled(void) {
@@ -413,7 +396,7 @@ size_t usb_vendor_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *d
     descriptor_counts->num_out_endpoints++;
     descriptor_counts->current_endpoint++;
 
-    usb_add_interface_string(*current_interface_string, vendor_interface_name);
+    usb_add_interface_name(*current_interface_string, NULL, vendor_interface_name);
     descriptor_buf[VENDOR_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 

shared-module/usb_hid/__init__.c

@@ -145,8 +145,6 @@ size_t usb_hid_descriptor_length(void) {
 
 // This is the interface descriptor, not the report descriptor.
 size_t usb_hid_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *descriptor_counts, uint8_t *current_interface_string, uint16_t report_descriptor_length, uint8_t boot_device) {
-    const char *usb_hid_interface_name;
-
     memcpy(descriptor_buf, usb_hid_descriptor_template, sizeof(usb_hid_descriptor_template));
 
     descriptor_buf[HID_DESCRIPTOR_INTERFACE_INDEX] = descriptor_counts->current_interface;
@@ -157,12 +155,7 @@ size_t usb_hid_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *desc
         descriptor_buf[HID_DESCRIPTOR_INTERFACE_PROTOCOL_INDEX] = boot_device; // 1: keyboard, 2: mouse
     }
 
-    if (custom_usb_hid_interface_name == NULL) {
-        usb_hid_interface_name = USB_INTERFACE_NAME " HID";
-    } else {
-        usb_hid_interface_name = custom_usb_hid_interface_name;
-    }
-    usb_add_interface_string(*current_interface_string, usb_hid_interface_name);
+    usb_add_interface_name(*current_interface_string, custom_usb_hid_interface_name, "HID");
     descriptor_buf[HID_DESCRIPTOR_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 

shared-module/usb_midi/__init__.c

@@ -163,11 +163,6 @@ char *custom_usb_midi_in_jack_name = NULL;
 char *custom_usb_midi_out_jack_name = NULL;
 
 size_t usb_midi_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *descriptor_counts, uint8_t *current_interface_string) {
-    const char *midi_streaming_interface_name;
-    const char *midi_audio_control_interface_name;
-    const char *midi_in_jack_name;
-    const char *midi_out_jack_name;
-
     memcpy(descriptor_buf, usb_midi_descriptor_template, sizeof(usb_midi_descriptor_template));
 
     descriptor_buf[MIDI_AUDIO_CONTROL_INTERFACE_NUMBER_INDEX] = descriptor_counts->current_interface;
@@ -191,43 +186,19 @@ size_t usb_midi_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *des
     descriptor_buf[MIDI_STREAMING_INTERFACE_NUMBER_INDEX_2] = descriptor_counts->current_interface;
     descriptor_counts->current_interface++;
 
-    if (custom_usb_midi_streaming_interface_name == NULL) {
-        midi_streaming_interface_name = USB_INTERFACE_NAME " MIDI";
-    } else {
-        midi_streaming_interface_name = custom_usb_midi_streaming_interface_name;
-    }
-
-    usb_add_interface_string(*current_interface_string, midi_streaming_interface_name);
+    usb_add_interface_name(*current_interface_string, custom_usb_midi_streaming_interface_name, "MIDI");
     descriptor_buf[MIDI_STREAMING_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 
-    if (custom_usb_midi_audio_control_interface_name == NULL) {
-        midi_audio_control_interface_name = USB_INTERFACE_NAME " Audio";
-    } else {
-        midi_audio_control_interface_name = custom_usb_midi_audio_control_interface_name;
-    }
-
-    usb_add_interface_string(*current_interface_string, midi_audio_control_interface_name);
+    usb_add_interface_name(*current_interface_string, custom_usb_midi_audio_control_interface_name, "Audio");
     descriptor_buf[MIDI_AUDIO_CONTROL_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 
-    if (custom_usb_midi_in_jack_name == NULL) {
-        midi_in_jack_name = USB_INTERFACE_NAME " usb_midi.ports[0]";
-    } else {
-        midi_in_jack_name = custom_usb_midi_in_jack_name;
-    }
-
-    usb_add_interface_string(*current_interface_string, midi_in_jack_name);
+    usb_add_interface_name(*current_interface_string, custom_usb_midi_in_jack_name, "usb_midi.ports[0]");
     descriptor_buf[MIDI_IN_JACK_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 
-    if (custom_usb_midi_out_jack_name == NULL) {
-        midi_out_jack_name = USB_INTERFACE_NAME " usb_midi.ports[0]";
-    } else {
-        midi_out_jack_name = custom_usb_midi_out_jack_name;
-    }
-
-    usb_add_interface_string(*current_interface_string, midi_out_jack_name);
+    usb_add_interface_name(*current_interface_string, custom_usb_midi_out_jack_name, "usb_midi.ports[0]");
     descriptor_buf[MIDI_OUT_JACK_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 

shared-module/usb_video/__init__.c

@@ -121,7 +121,7 @@ void shared_module_usb_video_swapbuffers(void) {
 }
 
 size_t usb_video_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *descriptor_counts, uint8_t *current_interface_string) {
-    usb_add_interface_string(*current_interface_string, "CircuitPython UVC");
+    usb_add_interface_name(*current_interface_string, NULL, "UVC");
     const uint8_t usb_video_descriptor[] = {
         #if CFG_TUD_VIDEO_STREAMING_BULK
         TUD_VIDEO_CAPTURE_DESCRIPTOR_UNCOMPR_BULK(*current_interface_string, descriptor_counts->current_endpoint | 0x80, usb_video_frame_width, usb_video_frame_height, DEFAULT_FRAME_RATE, 64, descriptor_counts->current_interface, descriptor_counts->current_interface + 1)

supervisor/shared/usb/usb_desc.c

@@ -49,6 +49,8 @@ typedef union {
 } interface_string_t;
 static interface_string_t collected_interface_strings[MAX_INTERFACE_STRINGS];
 
+// Bit n set: string n is a suffix to put after USB_INTERFACE_NAME and a space.
+static uint32_t prefixed_interface_strings;
 static size_t collected_interface_strings_length;
 static uint8_t current_interface_string;
 
@@ -289,20 +291,37 @@ static bool usb_build_configuration_descriptor(void) {
 }
 
 // str must not be on the heap.
-void usb_add_interface_string(uint8_t interface_string_index, const char str[]) {
+void usb_add_interface_name(uint8_t interface_string_index, const char *custom_name, const char *default_suffix) {
     if (interface_string_index > MAX_INTERFACE_STRINGS) {
         reset_into_safe_mode(SAFE_MODE_USB_TOO_MANY_INTERFACE_NAMES);
     }
 
+    const char *str = custom_name;
+    if (str == NULL) {
+        str = default_suffix;
+        prefixed_interface_strings |= 1u << interface_string_index;
+        collected_interface_strings_length += sizeof(USB_INTERFACE_NAME " ") - 1;
+    }
     collected_interface_strings[interface_string_index].char_str = str;
     collected_interface_strings_length += strlen(str);
 }
 
+void usb_add_interface_string(uint8_t interface_string_index, const char str[]) {
+    usb_add_interface_name(interface_string_index, str, NULL);
+}
+
 static const uint16_t language_id[] = {
     0x0304,
     0x0409,
 };
 
+static uint16_t *ascii_to_le16(uint16_t *dest, const char *str) {
+    while (*str) {
+        *dest++ = *str++;
+    }
+    return dest;
+}
+
 static bool usb_build_interface_string_table(void) {
     // Allocate space for the le16 String descriptors.
     // Space needed is 2 bytes for String Descriptor header, then 2 bytes for each character
@@ -322,22 +341,20 @@ static bool usb_build_interface_string_table(void) {
     // Start at 1 to skip the Language ID.
     for (uint8_t string_index = 1; string_index < current_interface_string; string_index++) {
         const char *str = collected_interface_strings[string_index].char_str;
-        const size_t str_len = strlen(str);
-        // 1 word for descriptor type and length, 1 word for each character.
-        const uint8_t descriptor_size_words = 1 + str_len;
-        const uint8_t descriptor_size_bytes = descriptor_size_words * 2;
-        string_descriptor[0] = 0x0300 | descriptor_size_bytes;
-
-        // Convert to le16.
-        for (size_t i = 0; i < str_len; i++) {
-            string_descriptor[i + 1] = str[i];
+        // Convert to le16 after 1 word for descriptor type and length.
+        uint16_t *end = string_descriptor + 1;
+        if (prefixed_interface_strings & (1u << string_index)) {
+            end = ascii_to_le16(end, USB_INTERFACE_NAME " ");
         }
+        end = ascii_to_le16(end, str);
+        const uint8_t descriptor_size_bytes = (end - string_descriptor) * 2;
+        string_descriptor[0] = 0x0300 | descriptor_size_bytes;
 
         // Save ptr to string descriptor with le16 str.
         collected_interface_strings[string_index].descriptor = string_descriptor;
 
         // Move to next descriptor slot.
-        string_descriptor += descriptor_size_words;
+        string_descriptor = end;
     }
     return true;
 }
@@ -358,6 +375,7 @@ bool usb_build_descriptors(const usb_identification_t *identification) {
     serial_number_hex_string[sizeof(serial_number_hex_string) - 1] = '\0';
 
     current_interface_string = 1;
+    prefixed_interface_strings = 0;
     collected_interface_strings_length = 0;
 
     return usb_build_device_descriptor(identification) &&

supervisor/shared/usb/usb_msc_flash.c

@@ -107,7 +107,7 @@ size_t usb_msc_descriptor_length(void) {
     return sizeof(usb_msc_descriptor_template);
 }
 
-static const char storage_interface_name[] = USB_INTERFACE_NAME " Mass Storage";
+static const char storage_interface_name[] = "Mass Storage";
 
 size_t usb_msc_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *descriptor_counts, uint8_t *current_interface_string) {
     memcpy(descriptor_buf, usb_msc_descriptor_template, sizeof(usb_msc_descriptor_template));
@@ -127,7 +127,7 @@ size_t usb_msc_add_descriptor(uint8_t *descriptor_buf, descriptor_counts_t *desc
     descriptor_counts->num_out_endpoints++;
     descriptor_counts->current_endpoint++;
 
-    usb_add_interface_string(*current_interface_string, storage_interface_name);
+    usb_add_interface_name(*current_interface_string, NULL, storage_interface_name);
     descriptor_buf[MSC_INTERFACE_STRING_INDEX] = *current_interface_string;
     (*current_interface_string)++;
 

supervisor/usb.h

@@ -47,6 +47,8 @@ typedef struct {
 // Shared implementation.
 bool usb_enabled(void);
 void usb_add_interface_string(uint8_t interface_string_index, const char str[]);
+// Add custom_name, or if it is NULL, USB_INTERFACE_NAME, a space, and default_suffix.
+void usb_add_interface_name(uint8_t interface_string_index, const char *custom_name, const char *default_suffix);
 bool usb_build_descriptors(const usb_identification_t *identification);
 bool usb_connected(void);
 void usb_disconnect(void);