Can't receive bytes sent via ByteArray in nRFConnect App

[morpho]

I created a custom BLE service following this tutorial and I am able to connect to the BLE service and write data to it, but ideally, I want to send character bytes as opposed to just decimal values. 

In the nRFConnect app, seemingly ByteArray is a field to enter character bytes but when I enter a character, on_write is invoked and p_evt_write->len remains 0, and so is p_evt_write->data. 
But when I send in an Unsigned field, I receive the expected data and so does the length.

Also can we not send multiple bytes at once? because otherwise p_evt_write->len would always remain 1 hence no actual use.

Am I using the ByteArray field correctly? 

[Einar Thorsrud]

Hi,

Can you say more about the characteristic you write to? What is the maximum length? I ask because referring to this snippet from the tutorial, the max length is set to sizeof(uint8_t), which is 1:

    /* This code belongs in custom_value_char_add() in ble_cus.c*/

    memset(&attr_char_value, 0, sizeof(attr_char_value));

    attr_char_value.p_uuid    = &ble_uuid;
    attr_char_value.p_attr_md = &attr_md;
    attr_char_value.init_len  = sizeof(uint8_t);
    attr_char_value.init_offs = 0;
    attr_char_value.max_len   = sizeof(uint8_t);

If you want to write more than one byte at a time, you must set a higher value for max_len.

[morpho]

max_len indicates the max number of bytes that could be sent before the application starts processing/interrupt is triggered then?  because currently, every byte I send, on_write is invoked through the ble event handler call.

Also now the RX characteristics button doesn't seem to recognize the tap to bring up the options for the data. do you see what's happening now?

[Einar Thorsrud]

The max_len here dictates the maximum length of the value, neither more or less. So it is not possible to send more than 1 byte at a time with this configuration. If you want to send data that is larger than 1 byte, you must increase the max_len.

Regarding the Rx characteristic I cannot see much from this video. Is there an error on the nRF side? For instance detected by an APP_ERROR_CHECK()? Have you debugged to check?

[morpho]

alright I am still not super clear on max_len and how it's working as my experience with the app has been a bit different. I set the max_len to 5 * sizeof(uint8_t), which means I should only be able to send 5 bytes assuming uint8_t is a byte, yes? when I do so, the app doesn't allow me to send.

This video is with max_len sizeof(uint8_t) * 50; (just randomly put in a number)

[Einar Thorsrud]

Hi,

morpho said:

I set the max_len to 5 * sizeof(uint8_t), which means I should only be able to send 5 bytes assuming uint8_t is a byte, yes?

Yes.

morpho said:

This video is with max_len sizeof(uint8_t) * 50; (just randomly put in a number)

I do not see in the video which characteristic you try to write to. Is it the correct one? Also, with byte array you should use hex characters, so not for instance "Hello" as you use.

[morpho]

Okay, so I tried again and despite having max_len at sizeof(uint8_t) * 5, I can send/receive < 5 bytes. Do you see why would that be? (p_evt_write->len < 5)

Secondly, there's no way for you to send string bytes? Would you have to consult to the ASCII table to make sure you're sending the expected chars?