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Table of Content


Preparing Firmware Image           

Create Private and Public Keys    

Add Related Source Files

Modify Source Codes     

Build Application              

SIGN SOTAFU Image       

Section Layout Configuration         

Section Change after Flash Download      

Section Change after OTA Firmware Upgrade       

OTA Upgrade Procedure

Upgrade Procedure         

Control Point Command Format 

Status Codes      

Sample Codes in Central Side       

Simple Introduction of Android Sample Codes


(Over-The-Air) Firmware Upgrade is a technology that a WICED Smart Device downloads an image from a central device (ex. Smart phone) over the (Bluetooth) air interface, and uses this image to upgrade its old firmware to a new one.

There are two kind of OTA Firmware Upgrade:

  • No Secure OTA Firmware Upgrade (OTAFU)
    • Only provides CRC32 check, to ensure the data integrity of downloaded image.
  • Secure OTA Firmware Upgrade (SOTAFU)
    • Use RSA public-key cryptography to provide a secure method to verify the downloaded image. If the image is not from the same manufacturer, or modified by third part, or some data error occurred in storage or in transmission, it can’t be upgraded successfully.

In WICED Smart SDK, we provide two kind of application for reference:

  • No Secure OTA Firmware Upgrade (OTAFU)
    • WICED-Smart-SDK\Apps\ota_firmware_upgrade
  • Secure OTA Firmware Upgrade (SOTAFU)
    • WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade.

For the convenience of description, we give a convention here:

  • Peripheral
    • A WICED Smart device.  In OTA Firmware Upgrade, the WICED Smart Device is played a GAP peripheral role.
  • Central
    • A device which a WICED Smart device can download an OTA image from, ex. A smart phone. In OTA Firmware Upgrade, this device is played a GAP central role.
  • Firmware Image
    • The image which to be downloaded into peripheral by UART or has be activated (will be loaded in RAM to run when reset device) in peripheral is call Firmware Image.
  • OTA Image
    • The image which to be downloaded from central and used to upgrade its firmware is call OTA Image.

Obviously, to support OTA Firmware Upgrade, it needs that:

  1. The peripheral (WICED Smart Device) must support OTA Firmware Upgrade function. Thus, it can download OTA Image from central, and upgrade its firmware.
  2. Generate an OTA Image.
  3. Central (ex. Smart Phone) can downloading the OTA Image into peripheral according to the procedure defined by peripheral.


  1. The SOTAFU is only available for devices that are based on BCM20737 chips, and in WICED Smart SDK 2.1.0 or later version.
  2. In this document, all of the examples are based on WICED Smart SDK 2.1.0.
  3. For earlier version, the OTA upgrading procedure may have some difference, so, you need to check the reference source codes in the corresponding SDK.
  4. In current WICES Smart SDK 2.1.0, we only download a new image into peripheral by UART or by OTA Firmware Upgrade.


Preparing Firmware Image

This section describes how to prepare a Firmware Image which supports OTA function in peripheral (WICED Smart Device), and an OTA Image which used to do OTA upgrading.

Note: You also can refer to document “WICED-Secure-Over-the-Air-Firmware-Upgrade.pdf” in WICED Smart SDK.

When building a WICED Smart application, it also generates an OTA Image. So we can prepare these two images at the same time.

As mentioned before, WICES Smart SDK provides OTA Firmware Upgrade application for reference, so we will reuse its source codes.

In here, we use Secure OTA Firmware Upgrade (SOTAFU) to illuminate. The steps in peripheral side are as below:

  1. Create a private and public key pair, and store it in a security place.
  2. Add the related source files into application project, and modify the makefile:
  3. Modify source codes to reuse the reference application’s source codes.
  4. Build the application, to generate Firmware Image and OTA Image.
  5. Sign the OTA Image with the private key generated in Step 1.

Note: For No Secure OTA Firmware Upgrade, we only need to skip the Step 1 and 5.

Create Private and Public Keys

WICED Smart SDK provides a tool to generate private and public key.

  • Tool Path
    • WICED-Smart-SDK\Tools\WsRsaKeyGen\[HOST_OS]\WsRsaKeyGen[Suffix]
    • For Windows, the path is “WICED-Smart-SDK\Tools\WsRsaKeyGen\WIN32\WsRsaKeyGen.exe”
  • Usage
    • Just execute the tool without parameters.
    • In Windows, run this program in Command Window or double click this program (Figure 1).


  . Seeding the random number generator...

  . Generating the private key ... ok

+ Press Enter to exit this program.

Figure 1: Generate Private and Public Key in Windows

This tool generates three files:

  • rsa.pri
    • Private Key, used to sign the raw OTA Image, to generate a SOTAFU OTA Image.
  • rsa.pub
    • Public Key, used to generate the source file “rsa_pub.c”. An intermediate file.
  • rsa_pub.c
    • The source file which used to add in the application project.
    • Define a Public Key array as shown in Figure 2, used to do signature verification.

File: rsa_pub.c (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)

unsigned char rsa_pub_key[] = {     0x01, 0x00, 0x01, 0x00,

0x95, 0xae, 0x1f, 0xbf, 0x9d, 0x85, 0xb5, 0x77, 0x2e, 0x1f, 0xa3, 0x5c, 0x9a, 0x1b, 0x85, 0x3e,


Figure 2: Source Codes of Public Key

Note: The private and public key pair is different in each time generated by the tool. If missing any files of them, obviously, the new OTA Image can’t be upgraded success thought the OTA Firmware Upgrade. Therefore, this two files need to be stored into a security place.

Add Related Source Files

  • Add necessary source files into application’s folder:
    • Put the generated source file “rsa_pub.c” into the application‘s folder.
    • Copy the following  four source files from folder “WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade” into the application’s folder:
      • ws_sec_upgrade_ota.c
      • Contains Secure OTA Service’s handling, and OTA Upgrade‘s flow and OTA Image data transfer control.
      • ws_sec_upgrade_ota.h
      • ws_upgrade.c
        • Contains the common function of writing the OTA Image into NVRAM, upgrading old Firmware to new one, activating new Firmware Image and reset device.
      • ws_upgrade.h

  • Modify the application’s makefile, add the above source files as the red part shown in Figure 3.

File: makefile.mk (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)


# Add Application sources here.


APP_SRC = hello_sensor.c   ws_sec_upgrade_ota.c   ws_upgrade.c   rsa_pub.c

Figure 3: Add Source Files in Makefile to build

Modify Source Codes

1. Add application’s version information.

    • Version information format (Figure 4)


  • When doing OTA Firmware Upgrade, it will compare the version information between Firmware Image and OTA Image. In principle, it is allowed to do upgrading only when it meets the following conditions:
    • Product ID must be same.
    • The new Major number must larger than or equal to the old one.
    • When Major number is equal, the new Minor must larger than the old one.

Note: In current’s source code’s design, the new Major number must larger than old one.

  • Define the variable of version information in source codes as shown in Figure 5.

This is the Firmware Image’s version information.

File: hello_sensor.c (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)

#define HELLO_SENSOR_APP_ID                                                  0x3A19

#define HELLO_SENSOR_APP_VERSION_MAJOR                  1

#define HELLO_SENSOR_APP_VERSION_MINOR                  1

const WS_UPGRADE_APP_INFO WsUpgradeAppInfo =


                /* ID                              = */ HELLO_SENSOR_APP_ID,

                /* Version_Major    = */ HELLO_SENSOR_APP_VERSION_MAJOR,

                /* Version_Minor    = */ HELLO_SENSOR_APP_VERSION_MINOR,


Figure 5: Define Version Information in Source Codes

File: ws_sec_upgrade_ota.h (src\apps\ota_secure_firmware_upgrade)

typedef struct


    UINT16 ID;

    UINT8  Version_Major;

    UINT8  Version_Minor;


Figure 6: Application Version Information Structure

2. Add Secure WICED Smart Upgrade Service into GATT Database.

The main mechanism of OTA Firmware Upgrade is that using GATT Characteristic to control the procedure and OTA Image data’s transfer. So we need to add Secure WICED Smart Upgrade Service into GATT Database

The Secure WICED Smart Upgrade Service characteristics’ Handle and UUID are defined in header file “ws_sec_upgrade_ota.h”.

The characteristics’ handle and name’s mapping and function is described as follow:

    • WICED Smart Secure Upgrade Service
      • A control point that central can sends commands to peripheral by written this characteristic. These commands are used to control the OTA Upgrade procedure.
      • Peripheral can send Handle Value Notification/Indication of this characteristic to inform central its command’s result.
      • Use to Enable/Disable Handle Value Notification/Indication.
      • If enable, peripheral can send Handle Value Notification/Indication to central.
      • Use to transfer OTA Image data.
      • Use to read application version information.
      • The value should be same as the version information defined before.

Add Secure WICED Smart Upgrade Service in the end of your application’s GATT database as the red part shown in Figure 7.

File: hello_sensor.c (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)

const UINT8 hello_sensor_gatt_database[]=




                CHARACTERISTIC_UUID128_WRITABLE (HANDLE_WS_UPGRADE_CHARACTERISTIC_CONTROL_POINT,                                                                   HANDLE_WS_UPGRADE_CONTROL_POINT,                                                                                                                                                   UUID_WS_SECURE_UPGRADE_CHARACTERISTIC_CONTROL_POINT,


                                    LEGATTDB_PERM_WRITE_REQ, 3),




                                    LEGATTDB_PERM_READABLE | LEGATTDB_PERM_WRITE_REQ, 2),





                                    LEGATTDB_PERM_VARIABLE_LENGTH | LEGATTDB_PERM_WRITE_REQ,  20),






                                    LEGATTDB_CHAR_PROP_READ, LEGATTDB_PERM_READABLE,  4),

                                    HELLO_SENSOR_APP_ID & 0xff, (HELLO_SENSOR_APP_ID >> 😎 & 0xff,                                                                                            HELLO_SENSOR_APP_VERSION_MAJOR, HELLO_SENSOR_APP_VERSION_MINOR,



Figure 7: Add Secure WICED Smart Upgrade Service In Source Codes

Note: If Handle definition of Secure WICED Smart Upgrade Service overlaps with your application’s others Handle, you need to re-define them in header file “ws_sec_upgrade_ota.h”.

3. Add initialization code and Write Characteristic handler.

In source file “ws_sec_upgrade_ota.c”, it provides each Handle of characteristic’s handler function. The mapping is as follow:

    • int ws_upgrade_ota_handle_command(UINT8 *data, int len);
    • int ws_upgrade_ota_handle_configuration (UINT8 *data, int len);
    • int ws_upgrade_ota_handle_data (UINT8 *data, int len);

The modification is as the red part shown in Figure 8.

File: hello_sensor.c (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)




                bleapp_set_cfg((UINT8 *)hello_sensor_gatt_database,


(void *)&hello_sensor_cfg,

(void *)&hello_sensor_puart_cfg,

(void *)&hello_sensor_gpio_cfg,



void hello_sensor_create(void)









int hello_sensor_write_handler(LEGATTDB_ENTRY_HDR *p)



                else if ((len >= 1) && (handle == HANDLE_WS_UPGRADE_CONTROL_POINT))


                                    return (ws_upgrade_ota_handle_command (attrPtr, len));


                else if ((len == 2) && (handle == HANDLE_WS_UPGRADE_CLIENT_CONFIGURATION_DESCRIPTOR))


                                    return (ws_upgrade_ota_handle_configuration (attrPtr, len));


                else if ((len > 0)  && (len <= WS_UPGRADE_MAX_DATA_LEN) && (handle == HANDLE_WS_UPGRADE_DATA))


                                    return (ws_upgrade_ota_handle_data (attrPtr, len));






                return 0;


  Figure 8: Add initialization code and Write Characteristic handler

Build Application

After building an application, in directory “WICED-Smart-SDK\build\[APP_BUILD_TARGET]”, it will generate three images:

    • Text describes the section and data. This file is used to flash image into peripheral by UART.
    • Application image, contains SS and DS section, and the DS section is the Firmware Image.
    • Intel HEX Format.
  • [APP_BUILD_TARGET].ota.hex
    • Text describes the section and data.  This file is used to generate OTA binary image.
    • Only contains DS section, the DS section is the OTA Image.
    • Intel HEX Format.
  • [APP_BUILD_TARGET].ota.bin
    • Binary of OTA Image.

In here,

[APP_BUILD_TARGET]   = [MAKE_TARGET]-rom-ram-Wiced-release


When create a new application’s make target, we need to specify its platform. All platforms are listed in folder “WICED-Smart-SDK\Platforms”. We can select one of them based on the chip on the board.

For example, the make target of application “ota_secure_firmware_upgrade” is “ota_secure_firmware_upgrade-BCM920737TAG_Q32 download”, so its [APP_NAME] is “ota_secure_firmware_upgrade”, [PLATFORM] is “BCM920737TAG_Q32”, and [APP_BUILD_TARGET] is “ota_secure_firmware_upgrade-BCM920737TAG_Q32-rom-ram-Wiced-release”.

Note: In the above case, the string “download” is a build parameter, it means that it will do downloading action after build success. If we don’t add this action string, it only does the code building. For more details, please refer “WICED-Smart-SDK\Makefile”.



WICED Smart SDK also provides sign tool.

  • Tool Path
    • WICED-Smart-SDK\Tools\WsRsaSign\[HOST_OS]\WsRsaSign[Suffix]
    • For Windows, the path is “WICED-Smart-SDK\Tools\WsRsaSign\WIN32\WsRsaSign.exe”
  • Usage
    • Command: WsRsaSign [Private Key] [OTA Image] [Product ID] [Major] [Minor]
      • [Private Key]
        • The path of “rsa.pri” file generated before.
      • [OTA Image]
        • The path of “*.ota.bin” file built in previous step.
      • [Product ID] [Major] [Minor]
        • The version information MUST be same as defined in source codes.
    • This tool generates a new image named “[OTA Image Name].signed”

Users\mudel\WICED\WICED-Smart-SDK-2.1.0\WICED-Smart-SDK\Tools\WsRsaSign\Win32>WsRsaSign.exe rsa.pri ota_secure_firmware_upgrade-BCM920737TAG_Q32-rom-ram-Wicedrelease.ota.bin 3A19 1 1

. Seeding the random number generator...

. Reading private key from 'rsa.pri'

. Generating the RSA/SHA-256 signature

. Done (created "ota_secure_firmware_upgrade-BCM920737TAG_Q32-rom-ram-Wicedrelease.ota.bin.signed")

Figure 9: Sign OTA Image

Secure OTA Firmware Image Format is as shown in Figure 10.


Section Layout Configuration

This section describes how to configure the NVRAM section to support OTA Firmware Upgrade.

Before to do this configuration, you need to configure the common section layout parameters in the BTP file as referred to document “WICED Smart BCM92073X EEPROM and SFLASH Layout.doc” first.

Obviously, if want to support OTA upgrade, we need a storage space to backup the original application Firmware Image in device, and a storage space to save the downloaded OTA Image, thus we can recover the firmware when the upgrading is interrupted by some unexpected event (ex. Power down).

Therefore, we use two DS that one is stored the current active Firmware Image and the another is used to store the downloaded OTA Image, to guarantee that even if the upgrading is interrupted, the original firmware still can work.

And, we also need one more SS section as a backup.

We need to configure its section layout in source codes as shown in Figure 11.

In Figure 11, “nv_loc_len[0]” is for EEPROM, and “nv_loc_len[1]” is for SFLASH.

The member of structure WS_UPGRADE_NV_LOC_LEN is as below:

  • ss_loc
    • The location (Start address) of SS1 and SS2.
  • ds1_loc
    • The location of DS1; It should be same as parameter “ConfigDSLocation” in BTP file.
  • ds1_len
    • The length of DS1.
  • ds2_loc
    • The location of DS2.
  • ds2_len
    • The length of DS2.  Generally, the length of DS1 and DS2 should be same.
  • vs1_loc
    • The location of VS1. It should be same as parameter “DLConfigVSLocation” in BTP file.
  • vs1_len
    • The length of VS1. It should be same as parameter “DLConfigVSLength” in BTP file.

File: ws_upgrade.c (WICED-Smart-SDK\Apps\ota_secure_firmware_upgrade)

const WS_UPGRADE_NV_LOC_LEN nv_loc_len[2] =



        /* .ss_loc = */     {0, 256},

        /* .ds1_loc = */    0x580,                   // ConfigDSLocation

        /* .ds1_len = */    0x7A00,                // ~31KB

        /* .ds2_loc = */    0x8000,

        /* .ds2_len = */    0x7A00,                // ~31KB

        /* .vs1_loc = */    0x140,                    // DLConfigVSLocation

/* .vs1_len = */    0x400,                // DLConfigVSLength                                            

        /* .vs2_loc = */    0,                             // No VS2 for EEPROMS

        /* .vs2_len = */    0                              // No VS2 for EEPROMS


    // We are assuming that we have a 64KByte Serial Flash. If the SF is larger, you may change ds1_len, ds2_loc, ds2_len

    // accordingly.


        /* .ss_loc = */      {0, 0x1000},

        /* .ds1_loc = */     0x4000,          // ConfigDSLocation

        /* .ds1_len = */     0x6000,

        /* .ds2_loc = */     0xA000,

        /* .ds2_len = */     0x6000,

        /* .vs1_loc = */     0x2000,          // DLConfigVSLocation

        /* .vs1_len = */     0x1000,          // DLConfigVSLength

        /* .vs2_loc = */     0x3000,

        /* .vs2_len = */     0x1000



Figure 11: Section Configuration for OTA Upgrade in Source Code

According the configuration in Figure 11, the section layout is as below:

EEPROM Section LayoutFigure12.png

  • Serial Flash Section Layout


Section Change after OTA Firmware Upgrade

In current design, the data size of SS section is 40 bytes. And its Byte 30-33 (The LSB (Least Significant Byte) is Byte 0.) records the DS’s start address. When the active DS section is changed, we need to modify these 4 bytes to point to the right address.

Section Change after Flash Download

As referred to document “WICED Smart BCM92073X EEPROM and SFLASH Layout.docx”, the application image “[APP_BUILD_TARGET].hex” contains two sections to indicate the flash download by UART. After flash download, the section layout is as shown in Figure 14.


Section Change after OTA Firmware Upgrade

As shown Figure 15, comparing “[APP_BUILD_TARGET].hex” and “[APP_BUILD_TARGET].ota.hex”, we can find “[APP_BUILD_TARGET].ota.hex” only have a DS section, and its data is same as “[APP_BUILD_TARGET].hex”, so the OTA Image only contains the DS section, and it upgrade mainly the DS section in OTA Upgrade.


Figure 15: The Comparing Between Firmware Image and OTA Image

The procedure when upgrading is as below:

  • Copy the download OTA image into the inactive or empty DS, and verify the image.
  • When the verification is passed, copy the active SS in RAM, and modify its 30-33 byte to point to the new DS, then save it to another SS.
  • Modify the current active SS as invalid/inactive, and the new SS as valid/active.

To be continued by WICED Smart BCM92073X OTA Firmware Upgrade (2)

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