Characteristic Attribute Read Callback does not return complete data buffer

RE: Characteristic Attribute Read Callback does not return complete data buffer

keegretupmoc — Fri, 03 Feb 2023 09:22:44 GMT

Hi Hung,

You can close this ticket. The data example I was given to transmit was a lot larger than was actually needed and ended up being less than 1/2 of the apparent 594 limitation. And it doesn't look like we will have anything else needing sizes that big. So we are up and running!

Thanks,

RE: Characteristic Attribute Read Callback does not return complete data buffer

Hung Bui — Thu, 29 Dec 2022 10:38:57 GMT

Hi Harold,

I don't know what could be wrong here but could you send us your sample code so we can test here ?
If you are sending large amount of data I would suggest to increase the ATT_MTU and data length. I don't think using CONFIG_BT_BUF_ACL_TX_SIZE = 27 would be the best, it would take much longer to send 755 bytes.

Have you looked at the configuration in the throughput example ?
I also made a throughput example to be tested with a phone here. It uses notification to send data, not read, but you can refer to the configuration.

I would also suggest to use our nRF Connect app on the phone to test.

Regarding your heap/stack size alignment, I don't think there is any issue with size of 2048. As far as I know the size just need to be divisible by 4.

RE: Characteristic Attribute Read Callback does not return complete data buffer

keegretupmoc — Thu, 29 Dec 2022 01:12:33 GMT

Btw,

Here are the heap/stack parameters I was talking about:

CONFIG_HEAP_MEM_POOL_SIZE=2048

CONFIG_BT_RX_STACK_SIZE=1024

CONFIG_BT_HCI_TX_STACK_SIZE=640

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=256

CONFIG_MAIN_STACK_SIZE=640

CONFIG_IDLE_STACK_SIZE=128

CONFIG_ISR_STACK_SIZE=1024

#CONFIG_BT_NUS_THREAD_STACK_SIZE=512

They are all from prj.conf. Let me know if they look ok. Also, I have reduced the CONFIG_HEAP_MEM_POOL_SIZE to 1024 because I am running out of memory. We probably need a bigger boat...

Thanks,

RE: Characteristic Attribute Read Callback does not return complete data buffer

keegretupmoc — Wed, 28 Dec 2022 23:26:39 GMT

Hung,

Here's the parameter info, et al:

CONFIG_BT_ATT_PREPARE_COUNT 0

CONFIG_BT_BUF_ACL_TX_SIZE 27

CONFIG_BT_BUF_ACL_RX_SIZE 69

CONFIG_BT_CTRL_DATA_LENGTH_MAX (not defined)

CONFIG_BT_L2CAP_TX_MTU 65

CONFIG_BT_L2CAP_TX_BUF_COUNT 2

The “client” I am using is a freeware test BLE scanner on an android phone. It’s called BLE Scanner by blue pixel technologies, version 3.21. We are working on an iOS app that will be talking to it, but it’s not quite ready yet.

I will work on a sniffer trace soon as well. I assume the transfer just stops at 594 due to some limitation, not really an error, so it is probably parameter settings as you probably already suspect.

I will try setting the CONFIG_BT_CTRL_DATA_LENGTH_MAX to something greater than 594 to see if that magically fixes it, since it isn't defined and may be defaulting to something around 600. Or some calculation based on other parameters.

Thanks,

RE: Characteristic Attribute Read Callback does not return complete data buffer

keegretupmoc — Wed, 28 Dec 2022 20:12:11 GMT

Hung,

Thanks for your response. I will work on getting you the additional information. I took over an existing app so I will need to do some research. I am more familiar with the TI BLE processors, but coming up to speed on Nordic.

I did have a question having to do with buffers, etc. I thought I had read somewhere that the heap/stack needed to be aligned on 4 bytes (32 bit) and as such could only be 256, 1024, 4096, 16384 bytes. Is that correct? Because some of the parameters in prj.conf, I think one in particular, had "stack" in its name and was 2048, which if the alignment was true is incorrectly set. I will find that one in particular, and maybe list them out with their values to see what you think.

Thanks again,

RE: Characteristic Attribute Read Callback does not return complete data buffer

Hung Bui — Wed, 28 Dec 2022 10:40:21 GMT

Hi Harold,

You may want to capture a sniffer trace of the communication so that we can inspect the connection parameters.

Could you give us more information about the settings you have ? For example:
CONFIG_BT_ATT_PREPARE_COUNT

CONFIG_BT_BUF_ACL_TX_SIZE
CONFIG_BT_BUF_ACL_RX_SIZE

CONFIG_BT_CTLR_DATA_LENGTH_MAX

CONFIG_BT_L2CAP_TX_MTU

CONFIG_BT_L2CAP_TX_BUF_COUNT

Which device did you use as the client ? You may want to increase the Data length max and ATT MTU (CONFIG_BT_L2CAP_TX_MTU) to have higher over the air packet size.

RE: Characteristic Attribute Read Callback does not return complete data buffer

Jared — Fri, 23 Dec 2022 14:03:34 GMT

Hi there,

We're currently low in staff due to the Holiday season.

Please expect some delay in the handling of this case.

best regards

Jared