Make space reserved for bootloader smaller, add better comments about what needs changing

Author: gfwilliams

Makefile

@@ -1347,11 +1347,12 @@ ifeq ($(FAMILY), NRF52)
 
   ifdef USE_BOOTLOADER
   NRF_BOOTLOADER    = $(ROOT)/targetlibs/nrf5x/nrf5_singlebank_bl_hex/nrf52_s132_singlebank_bl.hex
-  NFR_BL_START_ADDR = 0x78000 # see dfu_gcc_nrf52.ld
+  NFR_BL_START_ADDR = 0x7A000 # see Makefile, dfu_gcc_nrf52.ld,  linker_nrf52_ble_espruino_bootloader.ld and dfu_types.h
   NRF_BOOTLOADER_SETTINGS = $(ROOT)/targetlibs/nrf5x/nrf5_singlebank_bl_hex/bootloader_settings_nrf52.hex # Writes address 0x7F000 with 0x01.
   ifdef BOOTLOADER
     # we're trying to compile the bootloader itself
     LINKER_FILE = $(NRF5X_SDK_PATH)/../nrf5x_linkers/dfu_gcc_nrf52.ld
+    OPTIMIZEFLAGS=-Os # try to reduce bootloader size
   else
     LINKER_FILE = $(NRF5X_SDK_PATH)/../nrf5x_linkers/linker_nrf52_ble_espruino_bootloader.ld
   endif

targetlibs/nrf5x/nrf5_sdk/components/libraries/bootloader_dfu/dfu_types.h

@@ -57,8 +57,8 @@
 
 
 #elif NRF52     
-        
-#define BOOTLOADER_REGION_START             0x00078000                  /**< This field should correspond to start address of the bootloader, found in UICR.RESERVED, 0x10001014, register. This value is used for sanity check, so the bootloader will fail immediately if this value differs from runtime value. The value is used to determine max application size for updating. */
+// see Makefile, dfu_gcc_nrf52.ld,  linker_nrf52_ble_espruino_bootloader.ld and dfu_types.h       
+#define BOOTLOADER_REGION_START             0x0007A000                  /**< This field should correspond to start address of the bootloader, found in UICR.RESERVED, 0x10001014, register. This value is used for sanity check, so the bootloader will fail immediately if this value differs from runtime value. The value is used to determine max application size for updating. */
 #define BOOTLOADER_SETTINGS_ADDRESS         0x0007F000                  /**< The field specifies the page location of the bootloader settings address. */
 #define BOOTLOADER_MBR_PARAMS_PAGE_ADDRESS  0x0007E000                  /**< The field specifies the page location of the mbr params page address. */