Add an Example config case study (ARMmbed#153)

Add tutorial for changing various settings.

Author: LiyouZhou

README.md

@@ -156,3 +156,62 @@ The firmware update candidates can be stored on an external sd card. The firmwar
 ## Debug
 
 Debug prints can be turned on by enabling the define `#define tr_debug(fmt, ...) printf("[DBG ] " fmt "\r\n", ##__VA_ARGS__)` in `source/bootloader_common.h` and setting the `ARM_UC_ALL_TRACE_ENABLE=1` macro on command line `mbed compile -DARM_UC_ALL_TRACE_ENABLE=1`.
+
+## Example config case study
+
+Scenario: Your target is NUCLEO_F429ZI. You have added extra functionality to the bootloader such that the size of the bootloader exceeded the default 32KiB. How to configure your bootloader and application so that everything still work together.
+
+### STEP 1: Design flash layout
+
+NUCLEO_F429ZI has 2MiB of flash, and its sector sizes are as follows: 4x16KiB, 1x64KiB, 7x128KiB, 4x16KiB, 1x64KiB, 7x128KiB.
+Because the bootloader is larger than 32KiB, it will take the first 3 sectors. The NVStore area can no longer take 2x16KiB sectors. Hence we will move NVSTORE to the last 2x128KiB sectors in the flash region. So we will end up with the following layout:
+
+```
+0x00000000 - 0x0000C000 Bootloader
+0x0000C000 - 0x0000C400 Application Header
+0x0000C400 - 0x001C0000 Application
+0x001C0000 - 0x001E0000 NVSTORE_1
+0x001C0000 - 0x00200000 NVSTORE_2
+```
+
+The update firmware candidate is still stored on sd-card.
+
+### STEP 2: Configure the bootloader
+
+Given the above flash layout the following configuration need to change in the mbed_app.json:
+
+1. "nvstore.area_1_address": "(0x08000000+(2*1024-2*128)*1024)"
+1. "nvstore.area_1_size": "(128*1024)"
+1. "nvstore.area_2_address": "(0x08000000+(2*1024-128)*1024)"
+1. "nvstore.area_2_size": "(128*1024)"
+1. "update-client.application-details": "(0x08000000+3*16*1024)"
+1. "application-start-address": "(0x08000000+(3*16+1)*1024)"
+1. "max-application-size" : "((1024*2-128*2-3*16-1)*1024)"
+
+Now compile your bootloader. Flash and run the bootloader, on the serial uart you will see the following printout:
+
+> Layout: <layout_no> <boot_loader_info_address>
+
+Keep a note of the `boot_loader_info_address` which we will use in the next step.
+
+### STEP 3: Configure the Pelion Cloud Client Application
+
+In mbed_app.json, change the following:
+
+1. "update-client.application-details" : "(0x08000000+3*16*1024)"
+1. "update-client.bootloader-details" : "<boot_loader_info_address>"
+
+In mbed_lib.json change the following:
+
+1. "sotp-section-1-address": "(0x08000000+(2*1024-2*128)*1024)",
+1. "sotp-section-1-size": "(128*1024)",
+1. "sotp-section-2-address": "(0x08000000+(2*1024-128)*1024)",
+1. "sotp-section-2-size": "(128*1024)"
+
+Also add the following in mbed_app.json:
+
+1. "target.app_offset": "0x800c400",
+1. "target.header_offset": "0x800c000",
+1. "target.bootloader_img": "<path_to_your_newly_built_image>"
+
+Now you can build the application following the [Pelion Device Management Platform Documentation](https://cloud.mbed.com/docs/current/updating-firmware/updating-end-to-end-tutorials.html).