What is the Max PDU for BLE Stack Function HCI_SendControllerToHostEvent

Hi Yang

Can you check if the ICall heap is exhausted when you send the message? Also, what is your configured MAX_PDU_SIZE?

Best wishes

Hi JXS,

Thanks for answering the question.

First, I set MAX_PDU_SIZE to 255 to enable the maximum MTU for BLE transmission.

Then in order to check if the ICall heap exhausted, I set HEAPMGR_METRICS as a defined preprocessor symbol, and I checked these heap global variables for each different PDU, here are the captures:

this is the capture after calling HCI_SendControllerToHostEvent for 0x0780 event, with PDU = 236 bytes

here is after the 0x067f event with PDU = 236 bytes

here is after the 0x0780 event with PDU = 237 bytes

here is after the 0x067f event with PDU = 237 bytes

here is after the 0x0780 event with PDU = 238 bytes

here is after the 0x067f event with PDU = 238 bytes

and then CC chip is blocked. From the captures, we can tell that ICall Heap is not exhausted (heapmgrMemMax<HEAPMGR_SIZE), and there is a problem when PDU = 238 bytes for the first 0x0780 event.

So I use Step_Into to debug the HCI_SendControllerToHostEvent function, I found that behind this function, the first osal_msg_allocate function called to allocate memory for message header has the problem with its parameter 'uint16 len' . 

When PDU = 236 bytes, HCI_SendControllerToHostEvent function gives 0x00FE for 'len'

When PDU = 237 bytes, HCI_SendControllerToHostEvent function gives 0x00FF for 'len'

However, when PDU = 238 bytes, HCI_SendControllerToHostEvent function gives 0x0000 for 'len'

And when PDU = 239 bytes, HCI_SendControllerToHostEvent function gives 0x0001 for 'len'

I think there is something wrong with this part.

Looking forward to your further answer.

Best regards,

Yang

Hi Yang,

I am unsure about what you are trying to test. The TI BLE Software Developer's Guide covers how to setup your device in order to enable a larger PDU in Section 5.5.2.1 Configuring for Larger MTU values. Did you follow the steps given in the guide?

If you read the L2CAP section in the User's Guide you will see that MAX_PDU_SIZE can be up to 255 bytes. That is the maximum amount of data that can be sent between the Host and the Controller. That is different than the maximum amount of User Data you can sent from the Application to the Controller. The difference is due to overhead created by L2CAP and GATT headers. L2CAP headers are 4 bytes. GATT headers depend on what command you are sending. You can see the Bluetooth Core Spec v4.2 for information about header sizes for various requests.

I was able to write a 248 byte value over the air by doing the following:

1. Using Host Test -> define MAX_PDU_SIZE=255
2. Using Project Zero -> define MAX_PDU_SIZE=255
3. In Project Zero data_service.h, changed DS_STRING_LEN to 248
4. Using BTool, connect to the device running Project Zero
5. Perform a GATT_Exchange MTU with a clientRxMTU parameter of 255. This gets negotiated to 251 because the L2CAP header is subtracted.
6.  Perform a GATT discovery to find the handle of the String characteristic we modified in step 3. (should be listed as String Char)
7. Write a 248 byte value to the String Char.
8. You should see something similar to the below image. There should be 2 events that return success: GAP_HCI_ExtentionCommandStatus and ATT_WriteRsp

Hi Rachel,

Thanks very much for your answer.

My question is mainly about the function HCI_SendControllerToHostEvent that is used in the host_test project to send controller (CC2640) message to the Host (PC).

In order to test the Max Message Length that can be sent by this function from CC2640 to PC, I have modified the ble_dispatch.c like my above post. And then I found that, when even though we can receive 248 bytes from the air for a characteristic, these bytes can not be sent to PC by this function. 

From your answer, you said that the MAX_PDU_SIZE of 255 bytes is the maximum amount of data that can be sent between the Controller and the Host. For me, that means we can use HCI_SendConbtrllerToHostEvent to send at least 251 bytes to PC, right?  So could you please tell if my above test case has a problem of the use of HCI_SendControllerToHostEvent function? 

Looking forward to your further answer.

Best regards,

Yang

Hello. Can we take a step back here?  You're modifying code that is not generally intended to be changed and using functions that should only be used by the controller.  This is highly dangerous, is not easily supported, and there is likely a better way to do this.

What is the top-level goal here? Since you're using the HostTest project, you must be attempting to implement a network processor solution.  If you are trying to see how much data you can send over-the-air, this can be accomplished using pre-existing GATT commands and events as Rachel previously mentioned.

Or are you attempting to add some custom functionality to HostTest and send messages asynchronously to your application processor (HCITester in this case)?  If this is the case, you can use the NPI (network processor interface) layer. For example, you can call NPI_WriteTransport to encapsulate your custom message in an NPI frame to send over UART / SPI.

Perhaps you could give us an example of a message (i.e. just the bytes) that you are attempting to send from HostTest to HCITester and we can provide instructions on how to do this.

Hi Tim,

Thanks for the response.

What if I want to integrate a HCI_Custom_Command (exp: HCI_EXT_UTIL and HCI_EXT_PROFILE) that will be sent by HCITester from UART, how can I integrate the command in App? By using osal_msg_send function?

What I found as the exemple from Wiki is for CC2541: CC254X WITH EXT MCU and BLE HostTest Add Cmds. That's why I modified the ble_dispatch.c to support these custom commands.

Looking forward to your answer.

Best wishes,

Yang