how can i get the number BLE TX re transmissions

[ziv123]

hello Nordic

i am working with nrf52832 and nrf52840 socs, with ncs v2.1.0

i would like to know how many of the BLE packets i am sending has to be resent (and if it is possible to know the reason of resent, in case there is another reason beside packet missed some bytes/bits on the OTA way, that would be great as well ) 

any idea how can i get that info ?

also another question, if i move (with BLE 4.2 and above) to extended length packets, to increase throughput, should there be more resent packets since the risk of loosing data in a larger packet is greater ?

hope to read you soon

best regards

Ziv

[Sigurd]

Hi,

You can get this info as an QoS Connection Event Report.

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.3.0/nrfxlib/softdevice_controller/doc/api.html#c.sdc_hci_subevent_vs_qos_conn_event_report_t

This sample uses it to count crc mismatches:

https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/llpm/src/main.c#L312

[ziv123]

hi Sigurd

Sigurd said:

You can get this info as an QoS Connection Event Report.

i looked at the link you added and i have some questions, 

1. if i want the count of re-transmission i actually need to sum the count of naks, crc fails and rx timeouts ? is there a better way to get how many BLE packets i sent more then once ? 

2. when referring to event counter, does it counts number of connection event with in an established connection ? and does the above counts are counted within a connection event or throughout all the time the 2 devices are connected ? 

one clarification, i m tx'ing a lot of data so in one connection session i will probably have many BLE connection events  

3. if i can get the number of connection events, is it possible for me from one side (peripheral) to dictates / ask for a longer connection event in order to have less connection intervals and so more throughput ?

4. at some point i will move to BLE 4.2 or above on the non Nordic central and then i will be able to use extended BLE packet length, sending bigger packets, might result in more packets needed to be resend cause bigger packets may have greater risk of missing some data on transmission ?

hope to read you soon

best regards

Ziv

[Sigurd]

ziv123 said:

1. our connection interval is the minimum 7.5mlsec, is it enough time to get all the info summed (we also read data from external flash and build packets while transmitting) ?

Yeah, that shouldn't be a problem.

ziv123 said:

2. i did not understood from your question if i need to sum the

(nak count + crc_fail count + rx_timeout count = re tx count) , or am i missing something ? 

Yes, you need to sum it.

ziv123 said:

3.  if the report is per connection event then the event counter is llike a running index counting how many connection event there have been so far, meaning the last one is the total connection event happend in one connection session between 2 devices ?

One report will be generated every connection event. If you add some counter in your application, that you increment each time you get this event, then yes, that would be the total amount of connection events happened in one connection session between 2 devices.(Assuming your device is only connected to 1 device.)

ziv123 said:

the central does have the final say but if i want the peripheral to ask for longer connection events, how can i do it ?

By default, we extend the connection event as long as there are packets to be sent. If there is no more data to send, the connection event is closed. There is no option in the spec to ask the central for "longer connect events".

[ziv123]

hi Sigurd

i tried to use the same function as in the example, with some minor modifications. 

static bool on_vs_evt(struct net_buf_simple *buf)
{
    uint8_t                                      code;
    sdc_hci_subevent_vs_qos_conn_event_report_t *evt;

    code = net_buf_simple_pull_u8(buf);
    if (code != SDC_HCI_SUBEVENT_VS_QOS_CONN_EVENT_REPORT)
    {
        return false;
    }

    evt = (void *)buf->data;
    con_event_info.nak_count += evt->nak_count;
    con_event_info.crc_err_count += evt->crc_error_count;
    con_event_info.timeout_disconnection_count += evt->rx_timeout;

    con_event_info.con_event_count += evt->event_counter;

    return true;
}

static int enable_qos_conn_evt_report(void)
{
    int             err;
    struct net_buf *buf;

    err = bt_hci_register_vnd_evt_cb(on_vs_evt);
    if (err)
    {
        printk("Failed registering vendor specific callback (err %d)\n", err);
        return err;
    }

    sdc_hci_cmd_vs_qos_conn_event_report_enable_t *cmd_enable;

    buf = bt_hci_cmd_create(SDC_HCI_OPCODE_CMD_VS_QOS_CONN_EVENT_REPORT_ENABLE, sizeof(*cmd_enable));
    if (!buf)
    {
        printk("Could not allocate command buffer\n");
        return -ENOMEM;
    }

    cmd_enable = net_buf_add(buf, sizeof(*cmd_enable));
    cmd_enable->enable = true;

    err = bt_hci_cmd_send_sync(
        SDC_HCI_OPCODE_CMD_VS_QOS_CONN_EVENT_REPORT_ENABLE, buf, NULL);
    if (err)
    {
        printk("Could not send command buffer (err %d)\n", err);
        return err;
    }

    printk("Connection event reports enabled\n");
    return 0;
}

where should i put the ' enable_qos_conn_evt_report() ' call ? cause if i put it when i init the BLE here:

static void augu_com_start_ble(void)
{
    int rc;

    rc = STATS_INIT_AND_REG(smp_svr_stats, STATS_SIZE_32, "smp_svr_stats");
    __ASSERT(rc == 0, "failed in STATS_INIT_AND_REG");


    ///////////////////////
    enable_qos_conn_evt_report();
///////////////////////
#ifdef CONFIG_FILE_SYSTEM
    fs_mgmt_register_group();
    os_mgmt_register_group();
    img_mgmt_register_group();
    stat_mgmt_register_group();
#endif
    /* Enable Bluetooth. */
    rc = bt_enable(bt_ready);
    if (rc != 0)
    {
        AUGU_LOG_ERR("Bluetooth init failed (err %d)", rc);
        return;
    }

    bt_conn_cb_register(&conn_callbacks);

    /* Initialize the Bluetooth mcumgr transport. */
    smp_bt_register();

    commands_service_init();
#if defined(CONFIG_BOARD_CANARY_TYPE)
    testing_service_init();
#endif
    halo_svc_init();
    cts_init();

    if (IS_ENABLED(CONFIG_BT_SETTINGS))
    {
        settings_load();
    }

    k_sem_take(&bt_ready_sem, K_FOREVER);
}

then i get 

00> ASSERTION FAIL [err == 0] @ WEST_TOPDIR/zephyr/subsys/bluetooth/host/hci_core.c:327
00> 
00>   k_sem_take failed with err -11
00> 
00> [00000010] <err> os: r0/a1:  0x00000003  r1/a2:  0x00000002  r2/a3:  0x00000001
00> [00000010] <err> os: r3/a4:  0x20003cd8 r12/ip:  0x0000000a r14/lr:  0x00022087
00> [00000010] <err> os:  xpsr:  0x41000000
00> [00000010] <err> os: s[ 0]:  0x00000000  s[ 1]:  0x00000000  s[ 2]:  0x00000000  s[ 3]:  0x00000000
00> [00000010] <err> os: s[ 4]:  0x00000000  s[ 5]:  0x00000000  s[ 6]:  0x00000000  s[ 7]:  0x00000000
00> [00000010] <err> os: s[ 8]:  0x00000000  s[ 9]:  0x00000000  s[10]:  0x00000000  s[11]:  0x00000000
00> [00000010] <err> os: s[12]:  0x00000000  s[13]:  0x00000000  s[14]:  0x00000000  s[15]:  0x00000000
00> [00000010] [1;31m<err> os: fpscr:  0x20006518
00> [00000010] <err> os: r4/v1:  0x2002446c  r5/v2:  0x00000000  r6/v3:  0xfffffff5
00> [00000010] <err> os: r7/v4:  0x20022a10  r8/v5:  0x0000fd04  r9/v6:  0x20008250
00> [00000010] <err> os: r10/v7: 0x00000000  r11/v8: 0x00000000    psp:  0x200229a8
00> [00000010] <err> os: EXC_RETURN: 0x0
00> [00000010] <err> os: Faulting instruction address (r15/pc): 0x00022092
00> [00000046] <err> os: ***** HARD FAULT *****
00> [00000046] <err> os:   Debug event
00> [00000046] <err> os: r0/a1:  0x00000000  r1/a2:  0x00000000  r2/a3:  0x45524f43
00> [00000046] <err> os: r3/a4:  0x80000000 r12/ip:  0x0000000a r14/lr:  0x00054fb9
00> [00000046] <err> os:  xpsr:  0x8100000b
00> [00000046] <err> os: s[ 0]:  0x00000000  s[ 1]:  0x00000000  s[ 2]:  0x00000000  s[ 3]:  0x00000000
00> [00000046] <err> os: s[ 4]:  0x00000000  s[ 5]:  0x00000000  s[ 6]:  0x00000000  s[ 7]:  0x00000000
00> [00000046] [1;31m<err> os: s[ 8]:  0x00000000  s[ 9]:  0x00000000  s[10]:  0x00000000  s[11]:  0x00000000
00> [00000046] <err> os: s[12]:  0x00000000  s[13]:  0x00000000  s[14]:  0x00000000  s[15]:  0x00000000
00> [00000046] <err> os: fpscr:  0x200220e0
00> [00000046] <err> os: r4/v1:  0x20022158  r5/v2:  0x0000244d  r6/v3:  0x2000b5f4
00> [00000046] <err> os: r7/v4:  0x20022188  r8/v5:  0x200220f4  r9/v6:  0x00000003
00> [00000046] [1;31m<err> os: r10/v7: 0x00000003  r11/v8: 0x20022170    psp:  0x200229a8
00> [00000046] <err> os: EXC_RETURN: 0xffffffe1
00> [00000046] <err> os: Faulting instruction address (r15/pc): 0x0005430c
00> [00000046] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
00> [00000046] <err> os: Fault during interrupt handling
00> 
00> [00000046] <err> os: Current thread: 0x20006518 (main)[0m
00> [00000047] <err> fatal_error: Resetting system
00> *** Booting Zephyr OS build v3.1.99-ncs1  ***

if i move it to other place in the BLE init call:

static void augu_com_start_ble(void)
{
    int rc;

    rc = STATS_INIT_AND_REG(smp_svr_stats, STATS_SIZE_32, "smp_svr_stats");
    __ASSERT(rc == 0, "failed in STATS_INIT_AND_REG");

#ifdef CONFIG_FILE_SYSTEM
    fs_mgmt_register_group();
    os_mgmt_register_group();
    img_mgmt_register_group();
    stat_mgmt_register_group();
#endif
    /* Enable Bluetooth. */
    rc = bt_enable(bt_ready);
    if (rc != 0)
    {
        AUGU_LOG_ERR("Bluetooth init failed (err %d)", rc);
        return;
    }

    bt_conn_cb_register(&conn_callbacks);

    ///////////////////////
    enable_qos_conn_evt_report();
    ///////////////////////
    /* Initialize the Bluetooth mcumgr transport. */
    smp_bt_register();

    commands_service_init();
#if defined(CONFIG_BOARD_CANARY_TYPE)
    testing_service_init();
#endif
    halo_svc_init();
    cts_init();

    if (IS_ENABLED(CONFIG_BT_SETTINGS))
    {
        settings_load();
    }

    k_sem_take(&bt_ready_sem, K_FOREVER);
}

then i get '0' for all event report values (i know i am transferring data so there must be connection events and packet transfers).

if i put the enable qos call it in the 'connected' callback then again i get '0' for all values in the event report

(p.s. what qos and vs stands for ?)

hope to read you soon

best regards

Ziv 

[Sigurd]

Hi,

Take a look at how it's done here:

https://github.com/nrfconnect/sdk-nrf/blob/628de35443dff27f6915e718c6de2afe2b9015a5/samples/bluetooth/llpm/src/main.c#L492

ziv123 said:

(p.s. what qos and vs stands for ?)

qos = Quality of Service

vs = vendor specific

[ziv123]

Hi,

Sigurd said:

Take a look at how it's done here:

i took a look there, that's what i meant by :

ziv123 said:

i tried to use the same function as in the example, with some minor modifications. 

[Sigurd]

You are seeing on_vs_evt() beeing called, right?

But evt->event_counter is 0?

[ziv123]

Sigurd said:

You are seeing on_vs_evt() beeing called, right?

no, i added a counter to ' on_vs_evt() ' to counts how many times it is called (which should be equal to evt->event_counter i guess) and it is '0' as well, 

i also see that the enable function itself fails on 

int bt_hci_cmd_send_sync(uint16_t opcode, struct net_buf *buf,
			 struct net_buf **rsp)

in hci_core.c module (err -5 -> -EIO)

	status = cmd(buf)->status;
	if (status) {
		BT_WARN("opcode 0x%04x status 0x%02x", opcode, status);
		net_buf_unref(buf);

		switch (status) {
		case BT_HCI_ERR_CONN_LIMIT_EXCEEDED:
			return -ECONNREFUSED;
		default:
			return -EIO;
		}
	}

with:

0> [00000000] <wrn> bt_hci_core: opcode 0xfd04 status 0x01
00> [00000000] <err> COMM_MNG: Could not send command buffer (err -5)

haven't figure out why yet

when i tried to run the llpm example from my ncs (v2.1.0) with nrf52832 board, and i get different values for some reason i can't understand.. 

in the above pic is what i see in debug mode, i get a value inserted to the function 64772, and stepping in the function i see a different value - 3075, also the 'buf' values are different .. what am i missing ?? 

also it seems like the function ' enable_qos_conn_evt_report ' is called many times which is not clear to me yet, and the ' bt_hci_cmd_send_sync ' is called many times in it , not clear as well ??

hope to read you soon

best regards

Ziv

[ziv123]

ok, if i am correct then the issue is this config  ' CONFIG_BT_LL_SW_SPLIT '

which according to https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/connectivity/bluetooth/bluetooth-arch.html#bluetooth-build-types

means i am working with the zephyr BLE stack and not with the nrf connect SDK's softdevice.

please correct me if i am wrong

and if i understand correct then zephyr BLE LL des not support the connection event report, again, correct me if i am wrong

so..

1. is there an API to get BLE re transmissions count, while using zephyr BLE LL 

2. is there a build that enables work with both, if it is even possible to have 2 ble stacks work together, or is ti just enabling use of nordic libraries ?

3. if not, how complex should it be to migrate to work with the Nordic softdevice, is there some guide on the topic ?

p.s. regarding low latency, according to the table of Proprietary feature support in here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/softdevice_controller/README.html#softdevice-controller

 is it not dependent on the other side of the BLE connection, central/peripheral's ability to support that ?

hope to read you soon

best regards

Ziv

[Sigurd]

Hi,

ziv123 said:

and if i understand correct then zephyr BLE LL des not support the connection event report, again, correct me if i am wrong

Correct. The QoS Connection Event Report is a feature of the SoftDevice/MPSL stack.

ziv123 said:

1. is there an API to get BLE re transmissions count, while using zephyr BLE LL 

I'm not aware of any API for this for the Zephyr Controller.

ziv123 said:

2. is there a build that enables work with both, if it is even possible to have 2 ble stacks work together, or is ti just enabling use of nordic libraries ?

You can only have 1 stack enabled.

ziv123 said:

3. if not, how complex should it be to migrate to work with the Nordic softdevice, is there some guide on the topic ?

Set CONFIG_BT_LL_SW_SPLIT=n

ziv123 said:

 is it not dependent on the other side of the BLE connection, central/peripheral's ability to support that ?

To use the Low Latency Packet mode, you need to use nRF52 with LLPM support on both sides of the link.

[ziv123]

Hi,            

Sigurd said:

Set CONFIG_BT_LL_SW_SPLIT=n

this much i know,  but the the whole API used on our BLE comm module will have to change now 

and my question is is there some API correlation doc to switch to softdevice controller from zephyr controller ?

- what modules are used in softdevice that correlate and if i try to deep dive into my current zephyr controller APIs until i get to an NCS ones, could i just use them directly ? (not sure you can answer that but i am trying )

 - where can i find some comparison between the 2 BLE stacks cause changing the BLE stacks may change much more things in the connection and throughput etc. 

also i need to know if by moving to softdevice controller i am loosing some zephyr's controller features ? 

and lastly is it actually preferable to move to softdevice controller from currently implemented zephyr controller assuming we are going to keep on working with nrf52832 and nrf52840 for a list few more years ? what are the pros and cons of that transition ?

hope to read you soon

best regards

Ziv                           

[Sigurd]

ziv123 said:

this much i know,  but the the whole API used on our BLE comm module will have to change now 

I don't see why, Both the SoftDevice Controller and the Zephyr Controller, uses the Zephyr Bluetooth Host, and the Zephyr Bluetooth Host API can be used by both controllers.

ziv123 said:

also i need to know if by moving to softdevice controller i am loosing some zephyr's controller features ? 

I'm not aware of any features you might lose. Is there anything you have in mind ?

ziv123 said:

and lastly is it actually preferable to move to softdevice controller from currently implemented zephyr controller assuming we are going to keep on working with nrf52832 and nrf52840 for a list few more years ? what are the pros and cons of that transition ?

The SoftDevice Controller is the recommended controller. It's what we test and qualify.