added Makefile, linker script, and include files for GCC

.gitignore

@@ -4,3 +4,5 @@ D11bootloader THUMB Release/*
 D11bootloader THUMB Debug/*
 D11bootloader THUMB Release/*
 *.hzs
+make/build/*
+

Dx1bootloader.hzp

@@ -10,7 +10,7 @@
       arm_endian="Little"
       arm_fpu_type="None"
       arm_interwork="No"
-      arm_linker_heap_size="256"
+      arm_linker_heap_size="0"
       arm_linker_process_stack_size="0"
       arm_linker_stack_size="256"
       arm_simulator_memory_simulation_filename="$(TargetsDir)/SAM_D/Simulator/SAM_D_SimulatorMemory_$(HostOS)_$(HostArch)$(HostDLLExt)"
@@ -83,7 +83,7 @@
       arm_endian="Little"
       arm_fpu_type="None"
       arm_interwork="No"
-      arm_linker_heap_size="256"
+      arm_linker_heap_size="0"
       arm_linker_process_stack_size="0"
       arm_linker_stack_size="256"
       arm_simulator_memory_simulation_filename="$(TargetsDir)/SAM_D/Simulator/SAM_D_SimulatorMemory_$(HostOS)_$(HostArch)$(HostDLLExt)"

README.md

@@ -46,9 +46,16 @@ The USBCRM mode should be universal, as it doesn't depend on optional external c
 
 ## Requirements for compiling
 
-[Rowley Crossworks for ARM](http://www.rowley.co.uk/arm/) is presently needed to compile this code.  With Crossworks for ARM v4.3.2, compiling v1.03 using the Clang 7.0.0 compiler produces a 1022 byte image.  The more mainstream GCC does not appear to be optimized enough to produce an image that comes anywhere close to fitting into 1024 bytes.
+Pre-compiled images are already available via this project's Releases tab.
 
-There is no dependency in the code on the [Rowley Crossworks for ARM](http://www.rowley.co.uk/arm/) toolchain per se, but at this time I am not aware of any other ready-to-use Clang ARM cross-compiler package that I can readily point users to.
+[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.
+
+|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           |
+
+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.
 
 ## Programming targets with bootloader
 

bootloader.c

@@ -1,8 +1,8 @@
 /*
  * 1kByte USB DFU bootloader for Atmel SAMD11 microcontrollers
  *
- * Copyright (c) 2018, Peter Lawrence
- * Copyright (c) 2016, Alex Taradov <[email protected]>
+ * Copyright (c) 2018-2020, Peter Lawrence
+ * derived from https://github.com/ataradov/vcp Copyright (c) 2016, Alex Taradov <[email protected]>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -44,6 +44,7 @@
 #include "usb_descriptors.h"
 
 /*- Definitions -------------------------------------------------------------*/
+#define USE_DBL_TAP /* comment out to use GPIO input for bootloader entry */
 #define USB_CMD(dir, rcpt, type) ((USB_##dir##_TRANSFER << 7) | (USB_##type##_REQUEST << 5) | (USB_##rcpt##_RECIPIENT << 0))
 #define SIMPLE_USB_CMD(rcpt, type) ((USB_##type##_REQUEST << 5) | (USB_##rcpt##_RECIPIENT << 0))
 
@@ -145,7 +146,6 @@ static void USB_Service(void)
 
     usb_request_t *request = (usb_request_t *)udc_ctrl_out_buf;
     uint8_t type = request->wValue >> 8;
-    uint8_t index = request->wValue & 0xff;
     uint16_t length = request->wLength;
     static uint32_t *dfu_status = dfu_status_choices + 0;
 
@@ -213,7 +213,7 @@ static void USB_Service(void)
             dfu_status = dfu_status_choices + 2;
             dfu_addr = 0x400 + request->wValue * 64;
           }
-          /* fall through to below */
+          /* fall through */
         default: // DFU_UPLOAD & others
           /* 0x00 == DFU_DETACH, 0x04 == DFU_CLRSTATUS, 0x06 == DFU_ABORT, and 0x01 == DFU_DNLOAD and 0x02 == DFU_UPLOAD */
           if (!dfu_addr)
@@ -225,13 +225,15 @@ static void USB_Service(void)
   }
 }
 
-extern int __RAM_segment_used_end__;
-#define DBL_TAP_PTR (uint32_t *)(&__RAM_segment_used_end__)
-#define DBL_TAP_MAGIC 0xf02669ef
+#ifdef USE_DBL_TAP
+  extern int __RAM_segment_used_end__;
+  static volatile uint32_t *DBL_TAP_PTR = (volatile uint32_t *)(&__RAM_segment_used_end__);
+  #define DBL_TAP_MAGIC 0xf02669ef
+#endif
 
 void bootloader(void)
 {
-#ifndef DBL_TAP_MAGIC
+#ifndef USE_DBL_TAP
   /* configure PA15 (bootloader entry pin used by SAM-BA) as input pull-up */
   PORT->Group[0].PINCFG[15].reg = PORT_PINCFG_PULLEN | PORT_PINCFG_INEN;
   PORT->Group[0].OUTSET.reg = (1UL << 15);
@@ -250,7 +252,7 @@ void bootloader(void)
   if (DSU->DATA.reg)
     goto run_bootloader; /* CRC failed, so run bootloader */
 
-#ifndef DBL_TAP_MAGIC
+#ifndef USE_DBL_TAP
   if (!(PORT->Group[0].IN.reg & (1UL << 15)))
     goto run_bootloader; /* pin grounded, so run bootloader */