Summary

In part 6 of this series I will update the AnyCloud BLE Advertising Scanner to decode advertising packets into a more human readable textual output

Story

We are now 6 (or maybe 7 depending on how you count) articles into this series and we are still looking at raw bytes.  I have gotten to where I am pretty good at understanding those bytes, but that is now way to roll.  You might remember from the article on the IoT Expert Bluetooth Utility library that there were a some interesting functions defined in the header.  Here it is:

wiced_bool_t btutil_isEddystone(uint8_t *data);
wiced_bool_t btutil_is_iBeacon(uint8_t *data);
wiced_bool_t btutil_isCypress(uint8_t *data);

int btutil_adv_len(uint8_t *packet);
void btutil_adv_printPacketDecode(uint8_t *packet);
void btutil_adv_printPacketBytes(uint8_t *packet);

Lets transform our  project from part 6 to use these functions.  In this article I will

• Redo the print bytes (to be smarter) functionality and to use the built in function
• Rework the logic for the “print” command implementation
• Add a new command “decode” which will run the decode function

There are

All of the code can be found at git@github.com:iotexpert/AnyCloudBLEScanner.git and https://github.com/iotexpert/AnyCloudBLEScanner.git

There are git tags in place starting at part 5 so that you can look at just that version of the code.  "git tag" to list the tags.  And "git checkout part6" to look at the part 6 version of the code.

You can also create a new project with this is a template if you have the IoT Expert Manifest Files installed

Replace two code blocks with function calls

Do you remember this block of code?  It print’s out the 6-bytes of the Bluetooth Address.

    for(int i=0;i<BD_ADDR_LEN;i++)
    {
        printf("%02X:",adb_database[entry].result->remote_bd_addr[i]);
    }

You might have noticed that this function already exists in the BT Utility Library.  Use it.

    btutil_printBDaddress(adb_database[entry].result->remote_bd_addr);

Then you remember this block of code which iterates through and advertising packet and prints out the raw bytes?

// Print the RAW Data of the ADV Packet
    printf(" Data: ");
    int i=0;
    while(adb_database[entry].data[i])
    {
        for(int j=0;j<adb_database[entry].data[i];j++)
        {
            printf("%02X ",adb_database[entry].data[i+1+j]);
        }
        i = i + adb_database[entry].data[i]+1;
    }

Well, it exists in the library as well.  Use it.

btutil_adv_printPacketBytes(adb_database[entry].data);

Fix the “print” Command

In the previous implementation I had two functions for “print”.  The first one printed one entry and the second one printed the whole table.  I decided that I didnt really like this logic, so I compressed those two functions into one function.  Specifically, it take a number “entry”.  If that number is -1 then it will print the whole table.

static void adb_db_printRawPacket(int entry)
{
    int start,end;
 
    if(entry <= -1)
    {
        start = 0;
        end = adb_db_count;
    }
    else
    {
        start = entry;
        end = entry;
    }

    if(end>adb_db_count)
        end = adb_db_count; 

    for(int i=start;i<=end;i++)
    {
    
        printf("%02d MAC: ",i);
        btutil_printBDaddress(adb_database[i].result->remote_bd_addr);
        printf(" Data: ");
        btutil_adv_printPacketBytes(adb_database[i].data);

        printf("\n");
    }
}

Add a new “decode” Command

The next thing to do is to add a function to print out decoded packets (or the whole table).  So I wrote this:

static void adb_printDecodePacket(int entry)
{
    int start,end;
 
    if(entry == -1)
    {
        start = 0;
        end = adb_db_count;
    }
    else
    {
        start = entry;
        end = entry;
    }

    if(end>adb_db_count)
        end = adb_db_count; 

    for(int i=start;i<=end;i++)
    {

        printf("%02d MAC: ",i);
        btutil_printBDaddress(adb_database[i].result->remote_bd_addr);
        printf("\n");
        btutil_adv_printPacketDecode(adb_database[i].data);
        printf("\n");
    }
}

After finishing that block of code, I realized I had implemented almost exactly the same functionality which two different functions.  So, I decided to redo this by doing this.  Notice that it take in a adb_print_method, in other words raw bytes or decoded packet.

typedef enum {
    ADB_PRINT_METHOD_BYTES,
    ADB_PRINT_METHOD_DECODE,
} adb_print_method_t;

static void adb_db_print(adb_print_method_t method,int entry)
{
    int start,end;
 
    if(entry < 0)
    {
        start = 0;
        end = adb_db_count;
    }
    else
    {
        start = entry;
        end = entry;
    }

    if(end>adb_db_count)
        end = adb_db_count; 

    for(int i=start;i<=end;i++)
    {
    
        printf("%02d MAC: ",i);
        btutil_printBDaddress(adb_database[i].result->remote_bd_addr);
        switch(method)
        {
        
        case ADB_PRINT_METHOD_BYTES:
            printf(" Data: ");
            btutil_adv_printPacketBytes(adb_database[i].data);
        break;

        case ADB_PRINT_METHOD_DECODE:
            printf("\n");
            btutil_adv_printPacketDecode(adb_database[i].data);
        break;
        } 
        printf("\n");
    }
}

I don’t show it here, but after changing this I had to fix up the function calls in several places in the advDatabase.

Add a new command to print decode packets

Now that I have a new method to print packets, I add a command to the database to allow the user to call it:

typedef enum {
    ADB_ADD,
    ADB_PRINT_RAW,
    ADB_PRINT_DECODE,
} adb_cmd_t;

Then in the queue loop:

switch(msg.cmd)
            {
                case ADB_ADD:
                    scan_result = (wiced_bt_ble_scan_results_t *)msg.data0;
                    data = (uint8_t *)msg.data1;
                    adb_db_add(scan_result,data);
                break;
                case ADB_PRINT_RAW:
                    adb_db_print(ADB_PRINT_METHOD_BYTES,(int)msg.data0);
                break;
                case ADB_PRINT_DECODE:
                    adb_db_print(ADB_PRINT_METHOD_DECODE,(int)msg.data0);
                break;
            }

Then the actual function

void adb_printDecode(int entry)
{
    adb_cmdMsg_t msg;
    msg.cmd = ADB_PRINT_DECODE;
    msg.data0 = (void *)entry;
    xQueueSend(adb_cmdQueue,&msg,0); // If the queue is full... oh well
}

Then add it to advDatabase.h

void adb_printDecode(int entry);

Finally to the usercmd.c

static int usrcmd_printDecode(int argc, char **argv)
{
    if(argc == 1)
    {
        adb_printDecode(-1);
    }

    if(argc == 2)
    {
        int val;
        sscanf(argv[1],"%d",&val);
        adb_printDecode(val);
    }
    return 0;
}

Program and Test

When I actually program the scanner you can see that I can print out 1 item.  OR I can decode one item.  Notice that one contains 3 fields

• flags
• Tx Power Level
• Manufacturers data.  Apparently an Apple something or the other

And I can print the whole table

Or decode the whole table.