PSoC 6 BLE – Find Me Profile (Target)


I have been working on making some new videos for Cypress about the PSoC 6 BLE.  Everyone always likes to start with an easy BLE example, and the go to example is the “Find Me”.  I started by building a Find Me Profile example, but when I looked my example I decided that I wanted to trace the actual application all the way back to the Bluetooth Special Interest Group (SIG) specification.  So, that is exactly what I do for this article.

  • Bluetooth SIG Find Me Profile
  • Bluetooth SIG Immediate Alert Service
  • Configure PSoC 6 BLE Schematic & Pins
  • Setup FreeRTOS and Retarget I/O
  • PSoC 6 BLE Firmware Architecture
  • Firmware for the alertTask
  • Firmware for the Immediate Alert Service Callback
  • Firmware for the BLE Callback
  • Firmware for the BLE Task
  • Firmware to start the system

Bluetooth SIG Find Me Profile

The Bluetooth SIG defines a bunch of standard profiles.  A standard Profile is just some combination of standardized Services and Characteristics.  One of those Profiles is the Find Me Profile.  The concept behind the Find Me Profile was that you could connect to a device with the Find Me Profile, and then send it an alert, at which point it would start “alerting” (presumably blinking or beeping).  You could imagine a tag attached to your car keys for instance.  You can get the Find Me Profile Specification from the Bluetooth SIG website.  The spec is a 10ish page pdf that says a Find Me Profile is just a device with an Immediate Alert Service server or client.  Here is a picture from the spec:

The other interesting part of the specification defines how the advertising is supposed to work

Immediate Alert Service

But, what is an Immediate Alert Service?  Well, you can get the Immediate Alert Service specification from the Bluetooth SIG website as well.  It basically says that there is one Service called Immediate Alert with a UUID of 0x1802 and that Service has one Characteristic called “Alert Level” with a UUID of 0x2A06. Here is a screen shot.

Unfortunately the spec doesnt have the UUIDs in it, and you have to follow the [1] to the website.  On the Bluetooth SIG GATT Services UUID definition webpage you can see the UUID of the Immediate Alert Service (0x1802)

And on the Bluetooth SIG GATT Characteristics definition webpage you can see the UUID of the Alert Level (0x2A06)

It also says the alert characteristic is writable with three values (No, Mild, High) and if you click on Alert Level you can see the definition of those:

Next you can see information about the Alert Characteristic.

Configure PSoC 6 BLE Schematic & Pins

Now, lets build the project.  Create a new PSoC 6 BLE project and edit the schematic to have a BLE, UART, and two digital output pins (red, led9).

Assign the pins to the correct place on the CY8CKIT-062-BLE development kit.  I am going to use led9 to show when the device is connected (or not)

Change the build settings to add FreeRTOS (Heap 4) and Retarget I/O

Configure the BLE to be dual core and a peripheral

Add the Find Me Target (GATT Server) profile

Once that is done you will see the Immediate Alert Service (with the correct UUID from above)

And the Alert Level with the correct UUID

Next give the device a name (“FindMe”)

The spec calls for the advertising setup to be as follows

But I have to admit that I dont like to wait… so I configured it like this:

Next, configure the advertising packet to have the name of the device and the fact that it has a IAS Service

Setup FreeRTOS and Retarget I/O

Run “Generate Application” to bring in all of the BLE and PDL firmware.  Then edit “stdio_user.h” to setup the stdio support.

Next, modify FreeRTOSConfig.h to include support for semaphores.

and a much bigger stack

And finally the interrupts to support BLE

Firmware Architecture

There will be two tasks

  1. The alertTask which will be responsible for setting the state of the red LED.  To set the state of the LED any other task can set the EventGroup bits.
  2. The bleTask which will handle running the BLE and the generic BLE callback and the IAS callback.

Firmware for the alertTask

The alert task will

  1. Set things up including eventBits which I call “alertState”
  2. Turn off the red led
  3. Go into an infinite loop
  4. The loop will either 1) wait until the end of time or 2) timeout at 500ms)
  5. Then it will determine the cause of the timeout and set the state of the red LED

Firmware for the Immediate Alert Service Callback

Cypress setup a bunch of APIs that know how to handle a bunch of the Bluetooth SIG Profiles/Services.  First lets look at the PSoC 6 BLE Middleware PDL Documentation to find the IAS Service.  It is in the “BLE Service-Specific API” section.

We want to implement a “GATT Server”… meaning our device has the IAS Server running on it so that a GATT Client can write into our database.  When I click on “IAS Server Functions” it takes me to this section of the documentation.  Basically what you do in your firmware is

  1. Register a callback with Cy_BLE_IAS_RegisterAttrCallback
  2. Setup the function that will be called back when the Alert Level characteristic is written.

Here is the documentation for the callback.  You can see that you need to make a function that matches the prototype of “cy_ble_callback_t”)

When you are called back you will get a void * which you can then cast into a pointer of type “cy_stc_ble_ias_char_value_t *”.  This structure will contain the value of the alert in the “cy_stc_ble_gatt_value_t *value” member.

If you look at the “cy_stc_ble_Gatt_value_t” structure you will find that it contains a pointer to an array of uint8_t (actually one one)

Now to actually write the callback function.  It just:

  1. Looks and sees if it is a write callback
  2. finds the value using the “Cy_BLE_IASS_GetCharacteristicValue” function.
  3. Then sends a message to the alertTask

Instead of calling the function to get the values, you could have also been done this:

Firmware for the Ble Event Handler

The BLE event handler is really simple,  it just prints out some debugging information depending on the event.  It also starts the advertising when the stack starts or when it has been disconnected.

Firmware for the bleTask

The bleTask has two functions

  1. an ISR that is called whenever an IPC event happens (so that it can unlock the semaphore to process events)
  2. a main function which starts the system, registers the callback and runs process events at the right time.

Main Firmware

Finally the main firmware just starts all of the tasks.


After doing all of this, you can run CySmart to test the system: