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BLE advertisement does not work since minInterval and maxInterval are zero #1514

Closed cy-vaira closed 4 years ago

cy-vaira commented 5 years ago

Describe the bug BLE advertisement does not work with the BLE GATT Server demo.

System information

Expected behavior Device should appear on the list when scanned for BLE devices.

To reproduce Steps to reproduce the behavior: Please replace /cypress/boards/CY8CPROTO_062_4343W with any other board that supports BLE.

  1. Add #define IOT_BLE_ADD_CUSTOM_SERVICES ( 1 ) to vendors/cypress/boards/CY8CPROTO_062_4343W/aws_demos/config_files/iot_ble_config.h
  2. Open vendors/cypress/boards/CY8CPROTO_062_4343W/aws_demos/config_files/aws_demo_config.h, comment out #define CONFIG_MQTT_DEMO_ENABLED, and add #define CONFIG_BLE_GATT_SERVER_DEMO_ENABLED.
  3. Open vendors/cypress/boards/CY8CPROTO_062_4343W/aws_demos/config_files/aws_demo_config.h, update #define democonfigNETWORK_TYPES ( AWSIOT_NETWORK_TYPE_BLE)
  4. Open vendors/cypress/boards/CY8CPROTO_062_4343W/aws_demos/config_files/aws_iot_network_config.h and update #define configENABLED_NETWORKS ( AWSIOT_NETWORK_TYPE_BLE | AWSIOT_NETWORK_TYPE_WIFI )
  5. Build and Program.
  6. Once the device has started up, scan for the device using any BLE app.

Thank you!

cy-vaira commented 5 years ago

The issue is resolved when the .minInterval & .maxInterval of _advParams are set to non-zero value. This structure is in libraries/c_sdk/standard/ble/src/iot_ble_gap.c file. 

static IotBleAdvertisementParams_t _advParams =
{
    .includeTxPower    = true,
    .name              = { BTGattAdvNameShort,          IOT_BLE_DEVICE_SHORT_LOCAL_NAME_SIZE},
    .setScanRsp        = false,
    .appearance        = IOT_BLE_ADVERTISING_APPEARANCE,
    .minInterval       = IOT_BLE_ADVERTISING_CONN_INTERVAL_MIN,
    .maxInterval       = IOT_BLE_ADVERTISING_CONN_INTERVAL_MAX,
    .serviceDataLen    = 0,
    .pServiceData      = NULL,
    .manufacturerLen   = 0,
    .pManufacturerData = NULL,
    .pUUID1            = ( BTUuid_t * ) &_advUUID,
    .pUUID2            = NULL
};
lundinc2 commented 5 years ago

Hello @cy-vaira,

I am investigating this issue.

ravibhagavandas commented 5 years ago

Hi @cy-vaira

The connection intervals (min and max) is set to 0 to use the stack specific default values. Our BLE HAL layer API specification has this mentioned here, though I agree documentation is unclear.

I have added a PR to fix the documentation #1515

So the vendor implementation needs to use stack specific default values if the min and max connection intervals are set to 0.

Does that answer your question ?

cy-vaira commented 4 years ago

Hi @ravibhagavandas,

Thanks for the response. I believe end-users will be often configuring the connection interval parameters. What is the way for an end-user to do that?

ravibhagavandas commented 4 years ago

@cy-vaira

Thanks for your response.

After checking through the code, I think it should also pass inIOT_BLE_ADVERTISING_CONN_INTERVAL_MIN an IOT_BLE_ADVERTISING_CONN_INTERVAL_MAX as you described above (so that end user can configure the connection intervals). We are working on a fix for this.

ravibhagavandas commented 4 years ago

Hi @cy-vaira

I wanted to let you know that we have to revert back the above change for connection interval parameter in this PR #1545.

Reason being, the allowable size of the advertisement data is 31 bytes. With the existing parameters, advertisement data adds up to 30 bytes as follows

Service UUID 128 bit - 18 bytes (length - 1 byte, type -1 byte, value - 16 bytes)
Short local name - 6 bytes (length - 1 byte, type -1 byte, value - 4 bytes)
TX power - 3 bytes (length - 1 byte, type -1 byte, value - 1 byte)

So we have removed slave connection interval params from advertisement data (by setting the values to 0 in advertisement params) and enabling them in scan response data. The parameter is optional as per bluetooth specification and can be included in either advertisement or scan response data.

PR #1545 also updates the HAL API documentation mentioning the same.

cy-vaira commented 4 years ago

Hi @ravibhagavandas,

We see an issue with your solution. It's not a good idea to define the advertising interval via a macro (IOT_BLE_ADVERTISING_INTERVAL). Advertising interval is something user may want to change during the run time. For example, advertise rapidly for some time and switch to a lower advertising rate if no connection has been made. This is to save power.

Either there should be a GAP API to specify the advertising interval or the IotBleAdvertisementParams_t structure should have a member for specifying it.

ravibhagavandas commented 4 years ago

@cy-vaira

With the current HAL API, we don't expose this parameter to the user, since advertisement interval is a low level controller parameter and its often better for vendors to configure this with sane values based on power consumption. However the use case of setting advertisement intervals at run-time makes sense. We will look into how to best support this in our HAL layer.