diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 7edb1fcb..55bde832 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -30,7 +30,15 @@ jobs:
     steps:
     - name: Setup Python
       uses: actions/setup-python@v1
-
+    
+    - name: Cache MSP430 Toolchain
+      id: cache-msp430
+      uses: actions/cache@v1
+      with:
+        path: /tmp/dl/
+        # Increment serial number at end when updating downloads
+        key: msp430-${{ runner.os }}-0
+    
     - name: Setup Node.js
       uses: actions/setup-node@v1.1.0
       
@@ -44,23 +52,29 @@ jobs:
         echo "::add-path::`echo $HOME/opt/xPacks/@xpack-dev-tools/riscv-none-embed-gcc/*/.content/bin`"
 
         # TI MSP430 GCC
-        wget http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/MSPGCC/8_3_0_0/exports/msp430-gcc-8.3.0.16_linux64.tar.bz2 -O /tmp/msp430-gcc.tar.bz2
-        tar -C $HOME -xaf /tmp/msp430-gcc.tar.bz2
+        mkdir -p /tmp/dl/
+        [ -f "/tmp/dl/msp430-gcc.tar.bz2" ] || wget --progress=dot:mega http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/MSPGCC/8_3_0_0/exports/msp430-gcc-8.3.0.16_linux64.tar.bz2 -O /tmp/dl/msp430-gcc.tar.bz2
+        tar -C $HOME -xaf /tmp/dl/msp430-gcc.tar.bz2
         echo "::add-path::`echo $HOME/msp430-gcc-*_linux64/bin`"
 
         # ESP IDF
-        git clone https://github.com/espressif/esp-idf.git $HOME/esp-idf
+        git clone --depth 1 https://github.com/espressif/esp-idf.git $HOME/esp-idf
         cd $HOME/esp-idf
         ./install.sh
 
     - name: Checkout TinyUSB
       uses: actions/checkout@v2
-    
+      with:
+        # Cannot do submodule checkout here since LWIP's git server cannot checkout unadventised commits (it must use tags)
+        submodules: 'false'
+        
     - name: Checkout Submodules
       run: |
         git submodule sync --recursive
-        git submodule update --init --recursive
-    
+        # Special case LWIP since GNU's Savannah can't do shallow checkout of non-tagged commits
+        git submodule update --init --recursive lib/lwip
+        git submodule update --init --recursive --depth 1
+
     - name: Build
       run: |
         . $HOME/esp-idf/export.sh
diff --git a/examples/device/cdc_dual_ports/src/usb_descriptors.c b/examples/device/cdc_dual_ports/src/usb_descriptors.c
index 1b1d171b..03800d69 100644
--- a/examples/device/cdc_dual_ports/src/usb_descriptors.c
+++ b/examples/device/cdc_dual_ports/src/usb_descriptors.c
@@ -93,8 +93,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // 1st CDC: Interface number, string index, EP notification address and size, EP data address (out, in) and size.
   TUD_CDC_DESCRIPTOR(ITF_NUM_CDC1, 4, 0x81, 8, EPNUM_CDC, 0x80 | EPNUM_CDC, 64),
diff --git a/examples/device/cdc_msc/src/usb_descriptors.c b/examples/device/cdc_msc/src/usb_descriptors.c
index 12700822..7b22d46a 100644
--- a/examples/device/cdc_msc/src/usb_descriptors.c
+++ b/examples/device/cdc_msc/src/usb_descriptors.c
@@ -116,8 +116,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
   TUD_CDC_DESCRIPTOR(ITF_NUM_CDC, 4, EPNUM_CDC_NOTIF, 8, EPNUM_CDC_OUT, EPNUM_CDC_IN, 64),
diff --git a/examples/device/cdc_msc_freertos/src/usb_descriptors.c b/examples/device/cdc_msc_freertos/src/usb_descriptors.c
index 12700822..7b22d46a 100644
--- a/examples/device/cdc_msc_freertos/src/usb_descriptors.c
+++ b/examples/device/cdc_msc_freertos/src/usb_descriptors.c
@@ -116,8 +116,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
   TUD_CDC_DESCRIPTOR(ITF_NUM_CDC, 4, EPNUM_CDC_NOTIF, 8, EPNUM_CDC_OUT, EPNUM_CDC_IN, 64),
diff --git a/examples/device/dfu_rt/src/usb_descriptors.c b/examples/device/dfu_rt/src/usb_descriptors.c
index 17b3fe87..5cd661b2 100644
--- a/examples/device/dfu_rt/src/usb_descriptors.c
+++ b/examples/device/dfu_rt/src/usb_descriptors.c
@@ -141,8 +141,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
 #if CFG_TUD_CDC
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
diff --git a/examples/device/hid_composite/src/usb_descriptors.c b/examples/device/hid_composite/src/usb_descriptors.c
index 19689c90..6bde2ff7 100644
--- a/examples/device/hid_composite/src/usb_descriptors.c
+++ b/examples/device/hid_composite/src/usb_descriptors.c
@@ -101,8 +101,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, protocol, report descriptor len, EP In & Out address, size & polling interval
   TUD_HID_DESCRIPTOR(ITF_NUM_HID, 0, HID_PROTOCOL_NONE, sizeof(desc_hid_report), EPNUM_HID, CFG_TUD_HID_BUFSIZE, 10)
diff --git a/examples/device/hid_generic_inout/src/usb_descriptors.c b/examples/device/hid_generic_inout/src/usb_descriptors.c
index 87611a43..5c769c9c 100644
--- a/examples/device/hid_generic_inout/src/usb_descriptors.c
+++ b/examples/device/hid_generic_inout/src/usb_descriptors.c
@@ -99,8 +99,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, protocol, report descriptor len, EP In & Out address, size & polling interval
   TUD_HID_INOUT_DESCRIPTOR(ITF_NUM_HID, 0, HID_PROTOCOL_NONE, sizeof(desc_hid_report), EPNUM_HID, 0x80 | EPNUM_HID, CFG_TUD_HID_BUFSIZE, 10)
diff --git a/examples/device/midi_test/src/usb_descriptors.c b/examples/device/midi_test/src/usb_descriptors.c
index 94940482..72ab1416 100644
--- a/examples/device/midi_test/src/usb_descriptors.c
+++ b/examples/device/midi_test/src/usb_descriptors.c
@@ -90,8 +90,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP Out & EP In address, EP size
   TUD_MIDI_DESCRIPTOR(ITF_NUM_MIDI, 0, EPNUM_MIDI, 0x80 | EPNUM_MIDI, (CFG_TUSB_RHPORT0_MODE & OPT_MODE_HIGH_SPEED) ? 512 : 64)
diff --git a/examples/device/msc_dual_lun/src/usb_descriptors.c b/examples/device/msc_dual_lun/src/usb_descriptors.c
index 3b2615fd..9128c4f7 100644
--- a/examples/device/msc_dual_lun/src/usb_descriptors.c
+++ b/examples/device/msc_dual_lun/src/usb_descriptors.c
@@ -98,8 +98,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP Out & EP In address, EP size
   TUD_MSC_DESCRIPTOR(ITF_NUM_MSC, 0, EPNUM_MSC_OUT, EPNUM_MSC_IN, (CFG_TUSB_RHPORT0_MODE & OPT_MODE_HIGH_SPEED) ? 512 : 64),
diff --git a/examples/device/net_lwip_webserver/src/usb_descriptors.c b/examples/device/net_lwip_webserver/src/usb_descriptors.c
index a4eba205..6ce36cfe 100644
--- a/examples/device/net_lwip_webserver/src/usb_descriptors.c
+++ b/examples/device/net_lwip_webserver/src/usb_descriptors.c
@@ -107,8 +107,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, 0, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, 0, 100),
 
 #if CFG_TUD_NET == OPT_NET_ECM
   // Interface number, description string index, MAC address string index, EP notification address and size, EP data address (out, in), and size, max segment size.
diff --git a/examples/device/usbtmc/src/usb_descriptors.c b/examples/device/usbtmc/src/usb_descriptors.c
index 92b1dce6..67514026 100644
--- a/examples/device/usbtmc/src/usb_descriptors.c
+++ b/examples/device/usbtmc/src/usb_descriptors.c
@@ -165,8 +165,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
 #if CFG_TUD_CDC
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
diff --git a/examples/device/webusb_serial/src/usb_descriptors.c b/examples/device/webusb_serial/src/usb_descriptors.c
index 2925a66c..1a2df76c 100644
--- a/examples/device/webusb_serial/src/usb_descriptors.c
+++ b/examples/device/webusb_serial/src/usb_descriptors.c
@@ -95,8 +95,8 @@ enum
 
 uint8_t const desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
   TUD_CDC_DESCRIPTOR(ITF_NUM_CDC, 4, 0x81, 8, EPNUM_CDC, 0x80 | EPNUM_CDC, 64),
diff --git a/src/device/usbd.h b/src/device/usbd.h
index 07163a01..beeec7e1 100644
--- a/src/device/usbd.h
+++ b/src/device/usbd.h
@@ -156,9 +156,9 @@ TU_ATTR_WEAK bool tud_vendor_control_complete_cb(uint8_t rhport, tusb_control_re
 //------------- Configuration -------------//
 #define TUD_CONFIG_DESC_LEN   (9)
 
-// Interface count, string index, total length, attribute, power in mA
-#define TUD_CONFIG_DESCRIPTOR(_itfcount, _stridx, _total_len, _attribute, _power_ma) \
-  9, TUSB_DESC_CONFIGURATION, U16_TO_U8S_LE(_total_len), _itfcount, 1, _stridx, TU_BIT(7) | _attribute, (_power_ma)/2
+// Config number, interface count, string index, total length, attribute, power in mA
+#define TUD_CONFIG_DESCRIPTOR(config_num, _itfcount, _stridx, _total_len, _attribute, _power_ma) \
+  9, TUSB_DESC_CONFIGURATION, U16_TO_U8S_LE(_total_len), _itfcount, config_num, _stridx, TU_BIT(7) | _attribute, (_power_ma)/2
 
 //------------- CDC -------------//
 
diff --git a/src/osal/osal.h b/src/osal/osal.h
index 8b7527a7..94c71e7d 100644
--- a/src/osal/osal.h
+++ b/src/osal/osal.h
@@ -53,6 +53,8 @@ typedef void (*osal_task_func_t)( void * );
   #include "osal_freertos.h"
 #elif CFG_TUSB_OS == OPT_OS_MYNEWT
   #include "osal_mynewt.h"
+#elif CFG_TUSB_OS == OPT_OS_CUSTOM
+  #include "tusb_os_custom.h" // implemented by application
 #else
   #error OS is not supported yet
 #endif
diff --git a/src/tusb_option.h b/src/tusb_option.h
index 4a9d0571..6e2a2f12 100644
--- a/src/tusb_option.h
+++ b/src/tusb_option.h
@@ -93,9 +93,10 @@
 /** \defgroup group_supported_os Supported RTOS
  *  \ref CFG_TUSB_OS must be defined to one of these
  *  @{ */
-#define OPT_OS_NONE       1 ///< No RTOS
-#define OPT_OS_FREERTOS   2 ///< FreeRTOS
-#define OPT_OS_MYNEWT     3 ///< Mynewt OS
+#define OPT_OS_NONE       1  ///< No RTOS
+#define OPT_OS_FREERTOS   2  ///< FreeRTOS
+#define OPT_OS_MYNEWT     3  ///< Mynewt OS
+#define OPT_OS_CUSTOM     4  ///< Custom OS is implemented by application
 /** @} */
 
 
diff --git a/test/test/device/msc/test_msc_device.c b/test/test/device/msc/test_msc_device.c
index 43a8e743..095c2817 100644
--- a/test/test/device/msc/test_msc_device.c
+++ b/test/test/device/msc/test_msc_device.c
@@ -62,8 +62,8 @@ enum
 
 uint8_t const data_desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 
   // Interface number, string index, EP Out & EP In address, EP size
   TUD_MSC_DESCRIPTOR(ITF_NUM_MSC, 0, EDPT_MSC_OUT, EDPT_MSC_IN, (CFG_TUSB_RHPORT0_MODE & OPT_MODE_HIGH_SPEED) ? 512 : 64),
diff --git a/test/test/device/usbd/test_usbd.c b/test/test/device/usbd/test_usbd.c
index af30aaf8..06372b2e 100644
--- a/test/test/device/usbd/test_usbd.c
+++ b/test/test/device/usbd/test_usbd.c
@@ -73,8 +73,8 @@ tusb_desc_device_t const data_desc_device =
 
 uint8_t const data_desc_configuration[] =
 {
-  // Interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(0, 0, TUD_CONFIG_DESC_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+  // Config number, interface count, string index, total length, attribute, power in mA
+  TUD_CONFIG_DESCRIPTOR(1, 0, 0, TUD_CONFIG_DESC_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
 };
 
 tusb_control_request_t const req_get_desc_device =
@@ -211,8 +211,8 @@ void test_usbd_control_in_zlp(void)
   // ZLP must be return
   uint8_t zlp_desc_configuration[CFG_TUD_ENDOINT0_SIZE*2] =
   {
-    // Interface count, string index, total length, attribute, power in mA
-    TUD_CONFIG_DESCRIPTOR(0, 0, CFG_TUD_ENDOINT0_SIZE*2, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
+    // Config number, interface count, string index, total length, attribute, power in mA
+    TUD_CONFIG_DESCRIPTOR(1, 0, 0, CFG_TUD_ENDOINT0_SIZE*2, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),
   };
 
   desc_configuration = zlp_desc_configuration;