Optional split of jump address from start address (ARMmbed#104)

On targets like the NRF52, where the application's entry point is
not at the beginning of the firmware it is necessary to distinguish
between the two.

This commit adds an optional jump address to handle this corner
case. When the jump address is not defined the start address
becomes the default jump address.

README.md

@@ -25,10 +25,13 @@ NOTE: All these configurations must be set the same in the mbed cloud client whe
 ### Active Application and Header
 
 1. `update-client.application-details`, Address at which the metadata header of the active firmware is written. **Must align to flash erase boundary**
-1. `application-start-address`, Address at which The application starts **Must align to vector table size boundary and flash write page boundary**. It is assumed the region between `update-client.application-details` and `application-start-address` contains only the header. MUST be the same as "target.mbed_app_start" in the application.
+1. `application-start-address`, Address at which the application starts **Must align to vector table size boundary and flash write page boundary**.
+1. `application-jump-address`, Optional address for the application's entry point (vector table) if this is different from `application-start-address`.
 
 If the `application-start-address` is set less than one erase sector after the `update-client.application-details`, the two regions will be erased together. Otherwise the two regions will be erased separately in which case `application-start-address` must also align to **flash erase boundary**.
 
+If `application-jump-address` is not set, the `application-start-address` will be used as the application's entry point. The entry point MUST be the same as "target.mbed_app_start" in the application.
+
 ### Firmware Candidate Storage
 
 1. `MBED_CLOUD_CLIENT_UPDATE_STORAGE`, This need to be set in the "macros" section of `mbed_app.json`. Choices are ARM_UCP_FLASHIAP_BLOCKDEVICE and ARM_UCP_FLASHIAP. This determines whether the firmware is stored on a blockdevice or internal flash. If blockdevice is used `ARM_UC_USE_PAL_BLOCKDEVICE=1` must also be set. 

mbed_app.json

@@ -17,7 +17,11 @@
     ],
     "config": {
         "application-start-address": {
-            "help": "Address of the active application firmware in flash",
+            "help": "Address to the beginning of the active application firmware in flash",
+            "value": null
+        },
+        "application-jump-address": {
+            "help": "Jump address for running the active application firmware",
             "value": null
         },
         "max-application-size": {

source/main.cpp

@@ -71,6 +71,15 @@ SDBlockDevice sd(MBED_CONF_SD_SPI_MOSI, MBED_CONF_SD_SPI_MISO,
 BlockDevice* arm_uc_blockdevice = &sd;
 #endif
 
+#ifndef MBED_CONF_APP_APPLICATION_START_ADDRESS
+#error Application start address must be defined
+#endif
+
+/* If jump address is not set then default to start address. */
+#ifndef MBED_CONF_APP_APPLICATION_JUMP_ADDRESS
+#define MBED_CONF_APP_APPLICATION_JUMP_ADDRESS MBED_CONF_APP_APPLICATION_START_ADDRESS
+#endif
+
 int main(void)
 {
     /* Use malloc to allocate uint64_t version number on the heap */
@@ -167,15 +176,15 @@ int main(void)
         firmware_update_test_end();
 #endif
         uint32_t app_start_addr = MBED_CONF_APP_APPLICATION_START_ADDRESS;
-        uint32_t app_stack_ptr = *((uint32_t*)(app_start_addr + 0));
-        uint32_t app_jump_addr = *((uint32_t*)(app_start_addr + 4));
+        uint32_t app_stack_ptr = *((uint32_t*)(MBED_CONF_APP_APPLICATION_JUMP_ADDRESS + 0));
+        uint32_t app_jump_addr = *((uint32_t*)(MBED_CONF_APP_APPLICATION_JUMP_ADDRESS + 4));
 
         tr_info("Application's start address: 0x%" PRIX32, app_start_addr);
         tr_info("Application's jump address: 0x%" PRIX32, app_jump_addr);
         tr_info("Application's stack address: 0x%" PRIX32, app_stack_ptr);
         tr_info("Forwarding to application...\r\n");
 
-        mbed_start_application(app_start_addr);
+        mbed_start_application(MBED_CONF_APP_APPLICATION_JUMP_ADDRESS);
     }
 
     /* Reset bootCounter; this allows a user to reapply a new bootloader