make Crossworks compatible; increment bcdDevice in USB descriptor to make change evident

Author: majbthrd

README.md

@@ -48,12 +48,12 @@ The USBCRM mode should be universal, as it doesn't depend on optional external c
 
 Pre-compiled images are already available via this project's Releases tab.
 
-[Rowley Crossworks for ARM](http://www.rowley.co.uk/arm/) is presently suggested to compile this code, as it includes support for Clang; at this time, I am not aware of any other ready-to-use (and multi-OS to boot) Clang ARM cross-compiler package that I can readily point users to.  With Crossworks for ARM v4.6.1, compiling v1.05 using the Clang 9.0.1 compiler produces a 1003 byte image.  The more mainstream GCC lags behind Clang, although more recent GCC versions produce code that is less overweight than in years past.
+[Rowley Crossworks for ARM](http://www.rowley.co.uk/arm/) is presently suggested to compile this code, as it includes support for Clang; at this time, I am not aware of any other ready-to-use (and multi-OS to boot) Clang ARM cross-compiler package that I can readily point users to.  With Crossworks for ARM v4.8.1, compiling v1.06 using the Clang 11.1.0 compiler produces a 995 byte image.  The more mainstream GCC lags behind Clang, although more recent GCC versions produce code that is less overweight than in years past.
 
-|bootloader variant|Clang 9.0.1 (-O1) |GNU Arm 2018-q3 (-Os) |GNU Arm 2019-q4 (-Os) |
-|------------------|------------------|----------------------|----------------------|
-| USE_DBL_TAP      | 1003 bytes       | 1044 bytes (too big!)| 1041 bytes (too big!)|
-| GPIO input       | 979 bytes        | 1008 bytes           | 1006 bytes           |
+|bootloader variant|Clang 9.0.1 (-O1) |Clang 11.1.0 (-O1) |GNU Arm 2018-q3 (-Os) |GNU Arm 2019-q4 (-Os) |
+|------------------|------------------|-------------------|----------------------|----------------------|
+| USE_DBL_TAP      | 1003 bytes       | 995 bytes         | 1044 bytes (too big!)| 1041 bytes (too big!)|
+| GPIO input       | 979 bytes        | 975 bytes         | 1008 bytes           | 1006 bytes           |
 
 A Makefile supporting GCC is provided, but even if you have the latest GCC, it may not be able to output a version within the 1024 bytes available.  The latest GCC for ARM can be here: [GNU Arm Embedded Toolchain](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm).  Note that if you are adapting the Makefile for use with clang, try replacing the "-Os" argument in CFLAGS with something like "-O1" if the output size is larger than expected.
 

bootloader.c

@@ -227,7 +227,7 @@ static void USB_Service(void)
 
 #ifdef USE_DBL_TAP
   #define DBL_TAP_MAGIC 0xf02669ef
-  static volatile uint32_t __attribute__((section(".dont_move"))) double_tap;
+  static volatile uint32_t __attribute__((section(".vectors_ram"))) double_tap;
 #endif
 
 void bootloader(void)

linker/samd11d14.ld

@@ -69,7 +69,7 @@ SECTIONS
 
   .dont_move_block (NOLOAD): ALIGN(4)
   {
-    *(.dont_move)
+    *(.vectors_ram)
   }
 
   .data : ALIGN(4)