HID keyboard example - What does the buffer do and why it needs to be dequeued?

RE: HID keyboard example - What does the buffer do and why it needs to be dequeued?

MANGO — Thu, 12 Feb 2015 00:27:01 GMT

Hmm... Acutally, it does behave strange after I disconnect the device. I was facing that issue quite long. Anyway thanks for your detailed answer. I'll write the issue later or so.

RE: HID keyboard example - What does the buffer do and why it needs to be dequeued?

Håkon Alseth — Wed, 11 Feb 2015 15:29:13 GMT

If you try to send another char, it will then still send '0x0b' instead of your intended char, as it has not been de-queued from the buffer. It will still work in the sense that the program runs, but it would not behave as it should :-)

RE: HID keyboard example - What does the buffer do and why it needs to be dequeued?

MANGO — Tue, 10 Feb 2015 14:38:01 GMT

Pardon me Håkon.

In short I changed the code like this.

At button_event_handler, when I press a button,

I send one key. (For example, I send only 'h' at each press.)

static uint8_t my_key = 0x0b;

keys_send(1,& my_key);

After that I send 0 mask at BLE_EVT_TX_COMPLETE event and I did not call buffer_dequeue.

The code worked. Is this okay?

RE: HID keyboard example - What does the buffer do and why it needs to be dequeued?

MANGO — Mon, 09 Feb 2015 15:57:47 GMT

Thanks for the Desktop 2 solution. I'm afraid I understanded some parts incorrectly.

Does the original HID keyboard example sends "hello" all at once when I press a button? In my case, I receive one character per press. (h -> e -> l -> l -> o -> h -> e -> ...)
You mean the dequeue function's purpose is not to dequeue the buffers after buffer_enqueue was called? Does the dequeue function always has to be called at BLE_EVT_TX_COMPLETE regardless of buffer_enqueue was called or not?

Sorry to add more questions. I just want to implement a simple keyboard sending one key per button click.

RE: HID keyboard example - What does the buffer do and why it needs to be dequeued?

Håkon Alseth — Mon, 09 Feb 2015 14:19:36 GMT

Hi Mango,

This is not a ridiculous question.

The buffer functionality an complex solution to obtain something simple; loop through the string "hello" in a HID appropriate format. I have a reply to an older case here where I have explained a bit about this: devzone.nordicsemi.com/.../

If you do not dequeue in BLE_EVT_TX_COMPLETE (or BLE_GAP_EVT_DISCONNECT) you will go into the scenario where you do not flush your buffer. The next time you send a key, you will then be stuck at the first element, which is 'h', until you fill up your queue and the application stops working properly.

If you are looking for a solution to base your keyboard matrix upon, I would recommend looking at our nRFready Desktop 2 solution.

Cheers, Håkon