hibyr1: add USB DAC scaffolding

Introduce the generic, target-agnostic pieces for a gadget-driven USB
Audio Class DAC, gated by the HAVE_HOST_USB_AUDIO target flag so they stay
inert unless a target opts in.

Rather than adding a new USB mode, reuse the existing usb_audio setting
(never / always / while charge-only / while mass-storage) with its
LANG_USB_DAC string, usb_set_audio() callback and the
PCM_MIXER_CHAN_USBAUDIO mixer channel. HAVE_HOST_USB_AUDIO becomes the
umbrella capability flag for this common code; USB_ENABLE_AUDIO stays the
native usbstack class-driver contract (which needs HAVE_USBSTACK and so
cannot be used by hosted ports whose kernel owns the USB controller).

usb_set_audio() is declared here and implemented by the target (natively
by the usbstack driver, or in the hosted port for gadget targets, as with
usb_audio_get_active()), and applied at settings load. The playback
interlock in wps.c/playback.c keeps local playback from mixing with host
audio while the DAC is active. Simulator stubs for usb_set_audio() and
usb_audio_get_active() keep sim builds linking.

Co-Authored-By: Claude Opus 4.8
Change-Id: I5b7738508c24721d91d4c32379102a1ac7c6228b

apps/features.txt

@@ -313,7 +313,7 @@ codec_aac_he
 lto
 #endif
 
-#if defined(USB_ENABLE_AUDIO)
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
 usbdac
 #endif
 

apps/gui/wps.c

@@ -696,7 +696,7 @@ static inline int action_wpsab_single(long button)
 long gui_wps_show(void)
 {
 /* NOTE: if USBAudio ever gets its own DSP channel, this block can go away! */
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
     if (usb_audio_get_active())
     {
         splash(HZ*2, ID2P(LANG_USB_DAC_ACTIVE));

apps/menus/settings_menu.c

@@ -368,7 +368,7 @@ MENUITEM_SETTING(lineout_onoff, &global_settings.lineout_active, NULL);
 MENUITEM_SETTING(usb_hid, &global_settings.usb_hid, NULL);
 MENUITEM_SETTING(usb_keypad_mode, &global_settings.usb_keypad_mode, NULL);
 #endif
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
 MENUITEM_SETTING(usb_audio, &global_settings.usb_audio, NULL);
 #endif
 #if defined(USB_ENABLE_STORAGE) && defined(HAVE_MULTIDRIVE)
@@ -421,7 +421,7 @@ MAKE_MENU(usb_menu, ID2P(LANG_USB_MENU), 0, Icon_NOICON,
             &usb_hid,
             &usb_keypad_mode,
 #endif
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
             &usb_audio,
 #endif
 #if defined(USB_ENABLE_STORAGE) && defined(HAVE_MULTIDRIVE)
@@ -480,7 +480,7 @@ MAKE_MENU(system_menu, ID2P(LANG_SYSTEM),
             &sel_softlock,
 #endif
 #if defined(USB_ENABLE_HID) || \
-    defined(USB_ENABLE_AUDIO) || \
+    defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO) || \
     (defined(USB_ENABLE_STORAGE) && defined(HAVE_MULTIDRIVE)) || \
     defined(HAVE_USB_MODE)
             &usb_menu,

apps/playback.c

@@ -66,8 +66,11 @@
 #include <strings.h>  /* For strncasecmp() */
 #endif
 
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
 #ifdef USB_ENABLE_AUDIO
 #include "usbstack/usb_audio.h"
+#endif
+#include "usb.h"
 #include "splash.h"
 #include "lang.h"
 #endif
@@ -2993,7 +2996,7 @@ static void audio_start_playback(const struct audio_resume_info *resume_info,
  * a splash message to the user.
  * NOTE: if USBAudio ever gets its own DSP channel, this block can go away!
  */
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
     if (usb_audio_get_active())
     {
         queue_reply(&audio_queue, 0);

apps/settings.c

@@ -1128,6 +1128,9 @@ void settings_apply(bool read_disk)
 #if !defined(SIMULATOR) && !defined(USB_NONE) && (defined(HAVE_USB_ADB) || defined(HAVE_USB_POWER))
     usb_set_mode(global_settings.usb_mode);
 #endif
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
+    usb_set_audio(global_settings.usb_audio);
+#endif
 #if defined(HAVE_GENERAL_PURPOSE_LED)
     led_hw_on();
 #endif

apps/settings.h

@@ -814,7 +814,7 @@ struct user_settings
     int usb_keypad_mode;
 #endif
 
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
     int usb_audio;
 #endif
 

apps/settings_list.c

@@ -2310,7 +2310,7 @@ const struct settings_list settings[] = {
     ), /* CHOICE_SETTING( usb_keypad_mode ) */
 #endif
 
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
     CHOICE_SETTING(0, usb_audio, LANG_USB_DAC, 0, "usb-dac", "never,always,while_charge_only,while_mass_storage", usb_set_audio, 4,
         ID2P(LANG_NEVER), ID2P(LANG_ALWAYS), ID2P(LANG_WHILE_USB_CHARGE_ONLY), ID2P(LANG_WHILE_MASS_STORAGE_USB_ONLY)),
 #endif

firmware/export/pcm_mixer.h

@@ -71,7 +71,7 @@
 enum pcm_mixer_channel
 {
     PCM_MIXER_CHAN_PLAYBACK = 0,
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
     PCM_MIXER_CHAN_USBAUDIO,
 #endif
     PCM_MIXER_CHAN_VOICE,

firmware/export/usb.h

@@ -272,8 +272,15 @@ void usb_firewire_connect_event(void);
 void usb_set_hid(bool enable);
 #endif
 
-#ifdef USB_ENABLE_AUDIO
+#if defined(USB_ENABLE_AUDIO) || defined(HAVE_HOST_USB_AUDIO)
+/* Select when the USB Audio (DAC) function is active. Values follow the
+ * usb_audio setting: 0 never, 1 always, 2 while charge-only, 3 while
+ * mass-storage. Native targets use the usbstack driver; hosted targets
+ * (HiBy) drive their configfs gadget. */
 void usb_set_audio(int value);
+
+/* true while host-PCM (USB-DAC) playback is active */
+bool usb_audio_get_active(void);
 #endif
 
 #if defined(USB_ENABLE_STORAGE) && defined(HAVE_MULTIDRIVE)

uisimulator/common/stubs.c

@@ -202,6 +202,18 @@ bool usb_charging_enable(bool on)
 }
 #endif
 
+#if defined(HAVE_HOST_USB_AUDIO)
+void usb_set_audio(int value)
+{
+    (void)value;
+}
+
+bool usb_audio_get_active(void)
+{
+    return false;
+}
+#endif
+
 #ifdef HAVE_REMOTE_LCD_TICKING
 void lcd_remote_emireduce(bool state)
 {