Implement an evasion linear buffer for MCUs not capable for EP FIFO

Also MCUs using DMAs are within this list, however, these can use an EP
FIFO. There is just no time for implementation

src/class/audio/audio_device.c

@@ -125,6 +125,41 @@ typedef struct
 #if CFG_FIFO_MUTEX
   osal_mutex_def_t rx_ff_mutex[CFG_TUD_AUDIO_N_CHANNELS_RX];
 #endif
+#endif
+
+  // Evasion buffer in case target MCU is not capable of handling a ring buffer FIFO e.g. no hardware buffer is available or driver is would need to be changed dramatically
+#if ( CFG_TUSB_MCU == OPT_MCU_MKL25ZXX            || /* Intermediate software buffer required */                        \
+    CFG_TUSB_MCU == OPT_MCU_LPC18XX               || /* No clue how driver works */                                     \
+    CFG_TUSB_MCU == OPT_MCU_LPC43XX               ||                                                                    \
+    CFG_TUSB_MCU == OPT_MCU_MIMXRT10XX            ||                                                                    \
+    CFG_TUSB_MCU == OPT_MCU_RP2040)               || /* Don't want to change driver */                                  \
+    CFG_TUSB_MCU == OPT_MCU_VALENTYUSB_EPTRI      || /* Intermediate software buffer required */                        \
+    CFG_TUSB_MCU == OPT_MCU_CXD56                 || /* No clue how driver works */                                     \
+    CFG_TUSB_MCU == OPT_MCU_DA1469X               || /* Uses DMA - Ok for FIFO, had no time for implementation */       \
+    CFG_TUSB_MCU == OPT_MCU_NRF5X                 || /* Uses DMA - Ok for FIFO, had no time for implementation */       \
+    CFG_TUSB_MCU == OPT_MCU_LPC11UXX              || /* Uses DMA - Ok for FIFO, had no time for implementation */       \
+    CFG_TUSB_MCU == OPT_MCU_LPC13XX               || \
+    CFG_TUSB_MCU == OPT_MCU_LPC15XX               || \
+    CFG_TUSB_MCU == OPT_MCU_LPC51UXX              || \
+    CFG_TUSB_MCU == OPT_MCU_LPC54XXX              || \
+    CFG_TUSB_MCU == OPT_MCU_LPC55XX               || \
+    CFG_TUSB_MCU == OPT_MCU_LPC175X_6X            || \
+    CFG_TUSB_MCU == OPT_MCU_LPC40XX)
+
+#define USE_EVADE_BUFFER      1
+
+#if CFG_TUD_AUDIO_EP_OUT_SW_BUFFER_SIZE
+  CFG_TUSB_MEM_ALIGN uint8_t evasion_buf_out[CFG_TUD_AUDIO_EPSIZE_OUT];
+#endif
+
+#if CFG_TUD_AUDIO_EP_IN_SW_BUFFER_SIZE
+  CFG_TUSB_MEM_ALIGN uint8_t evasion_buf_in[CFG_TUD_AUDIO_EPSIZE_IN];
+#endif
+
+#endif
+
+#ifndef USE_EVADE_BUFFER
+#define  USE_EVADE_BUFFER     0
 #endif
 
 } audiod_interface_t;
@@ -292,7 +327,11 @@ static bool audiod_rx_done_cb(uint8_t rhport, audiod_interface_t* audio)
 #endif
 
   // Prepare for next transmission
+#if USE_EVADE_BUFFER
+  TU_VERIFY(usbd_edpt_xfer(rhport, audio->ep_out, &audio->evasion_buf_out, CFG_TUD_AUDIO_EPSIZE_OUT), false);
+#else
   TU_VERIFY(usbd_edpt_iso_xfer(rhport, audio->ep_out, &audio->ep_out_ff, CFG_TUD_AUDIO_EP_OUT_SW_BUFFER_SIZE), false);
+#endif
 
   // Call a weak callback here - a possibility for user to get informed decoding was completed
   if (tud_audio_rx_done_post_read_cb) TU_VERIFY(tud_audio_rx_done_post_read_cb(rhport, n_bytes_received, idxDriver, audio->ep_out, audio->altSetting[idxItf]));
@@ -485,7 +524,12 @@ static bool audiod_tx_done_cb(uint8_t rhport, audiod_interface_t * audio)
   uint16_t n_bytes_tx = tu_fifo_count(&audio->ep_in_ff);
 
   // Schedule transmit
+#if USE_EVADE_BUFFER
+  tu_fifo_write_n(&audio->ep_in_ff, &audio->evasion_buf_in, n_bytes_tx);
+  TU_VERIFY(usbd_edpt_xfer(rhport, audio->ep_in, &audio->evasion_buf_in, n_bytes_tx));
+#else
   TU_VERIFY(usbd_edpt_iso_xfer(rhport, audio->ep_in, &audio->ep_in_ff, n_bytes_tx));
+#endif
 
   // Call a weak callback here - a possibility for user to get informed former TX was completed and how many bytes were loaded for the next frame
   if (tud_audio_tx_done_post_load_cb) TU_VERIFY(tud_audio_tx_done_post_load_cb(rhport, n_bytes_tx, idxDriver, audio->ep_in, audio->altSetting[idxItf]));
@@ -815,7 +859,11 @@ static bool audiod_set_interface(uint8_t rhport, tusb_control_request_t const *
             if (tud_audio_set_itf_cb) TU_VERIFY(tud_audio_set_itf_cb(rhport, p_request));
 
             // Prepare for incoming data
-            TU_VERIFY(usbd_edpt_iso_xfer(rhport, _audiod_itf[idxDriver].ep_out, &_audiod_itf[idxDriver].ep_out_ff, CFG_TUD_AUDIO_EP_OUT_SW_BUFFER_SIZE), false);
+#if USE_EVADE_BUFFER
+            TU_VERIFY(usbd_edpt_xfer(rhport, _audiod_itf[idxDriver].ep_out, &_audiod_itf[idxDriver].evasion_buf_out, CFG_TUD_AUDIO_EPSIZE_OUT), false);
+#else
+            TU_VERIFY(usbd_edpt_iso_xfer(rhport, _audiod_itf[idxDriver].ep_out, &_audiod_itf[idxDriver].ep_out_ff, CFG_TUD_AUDIO_EPSIZE_OUT), false);
+#endif
           }
 
 #if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
@@ -1106,6 +1154,11 @@ bool audiod_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint3
     {
       // Save into buffer - do whatever has to be done
       //      TU_VERIFY(audiod_rx_done_cb(rhport, &_audiod_itf[idxDriver], _audiod_itf[idxDriver].ep_out_buf, xferred_bytes));
+
+#if USE_EVADE_BUFFER
+      TU_VERIFY(tu_fifo_write_n(&_audiod_itf[idxDriver].ep_out_ff, &_audiod_itf[idxDriver].evasion_buf_out, (uint16_t) xferred_bytes)); // Copy data into FIFO
+#endif
+
       TU_VERIFY(audiod_rx_done_cb(rhport, &_audiod_itf[idxDriver]));
 
       return true;