ble_app_att_mtu_throughput in details

[Ste_]

Hi, 

I'm using ble_app_att_mtu_throughput to communicate some data from a nRF52832 to another one. I reached my goal (1.4Mbps) but now I would know what the two board communicate. 

I menaged the code in particular: 

in amt.h:

#define AMT_BYTE_TRANSFER_CNT               (244 * 5)

instead of: 

#define AMT_BYTE_TRANSFER_CNT               (1024 * 1024)

just to manage well my 244 byte packets;

in the last part of amts.c I changed 244 with 1024, so:

static void char_notification_send(nrf_ble_amts_t * p_ctx)
{
    uint8_t            data[256];
    uint16_t           payload_len = p_ctx->max_payload_len;
    nrf_ble_amts_evt_t evt;

    if (p_ctx->bytes_sent >= AMT_BYTE_TRANSFER_CNT)
    {
        evt.bytes_transfered_cnt = p_ctx->bytes_sent;
        evt.evt_type             = NRF_BLE_AMTS_EVT_TRANSFER_FINISHED;

        p_ctx->evt_handler(evt);

        p_ctx->busy        = false;
        p_ctx->bytes_sent  = 0;
        p_ctx->kbytes_sent = 0;

        return;
    }

    ble_gatts_hvx_params_t const hvx_param =
    {
        .type   = BLE_GATT_HVX_NOTIFICATION,
        .handle = p_ctx->amts_char_handles.value_handle,
        .p_data = data,
        .p_len  = &payload_len,
    };

    uint32_t err_code = NRF_SUCCESS;
    while (err_code == NRF_SUCCESS)
    {
        (void)uint32_encode(p_ctx->bytes_sent, data);

        err_code = sd_ble_gatts_hvx(p_ctx->conn_handle, &hvx_param);

        if (err_code == NRF_ERROR_RESOURCES)
        {
            // Wait for BLE_GATTS_EVT_HVN_TX_COMPLETE.
            p_ctx->busy = true;
            break;
        }
        else if (err_code != NRF_SUCCESS)
        {
            NRF_LOG_ERROR("sd_ble_gatts_hvx() failed: 0x%x", err_code);
        }

        p_ctx->bytes_sent += payload_len;

        if (p_ctx->kbytes_sent != (p_ctx->bytes_sent / 244))
        {
            p_ctx->kbytes_sent = (p_ctx->bytes_sent / 244);

            evt.evt_type             = NRF_BLE_AMTS_EVT_PACKET_244B;
            evt.bytes_transfered_cnt = p_ctx->bytes_sent;
            p_ctx->evt_handler(evt);
        }
    }
}

instead of: 

static void char_notification_send(nrf_ble_amts_t * p_ctx)
{
    uint8_t            data[256];
    uint16_t           payload_len = p_ctx->max_payload_len;
    nrf_ble_amts_evt_t evt;

    if (p_ctx->bytes_sent >= AMT_BYTE_TRANSFER_CNT)
    {
        evt.bytes_transfered_cnt = p_ctx->bytes_sent;
        evt.evt_type             = NRF_BLE_AMTS_EVT_TRANSFER_FINISHED;

        p_ctx->evt_handler(evt);

        p_ctx->busy        = false;
        p_ctx->bytes_sent  = 0;
        p_ctx->kbytes_sent = 0;

        return;
    }

    ble_gatts_hvx_params_t const hvx_param =
    {
        .type   = BLE_GATT_HVX_NOTIFICATION,
        .handle = p_ctx->amts_char_handles.value_handle,
        .p_data = data,
        .p_len  = &payload_len,
    };

    uint32_t err_code = NRF_SUCCESS;
    while (err_code == NRF_SUCCESS)
    {
        (void)uint32_encode(p_ctx->bytes_sent, data);

        err_code = sd_ble_gatts_hvx(p_ctx->conn_handle, &hvx_param);

        if (err_code == NRF_ERROR_RESOURCES)
        {
            // Wait for BLE_GATTS_EVT_HVN_TX_COMPLETE.
            p_ctx->busy = true;
            break;
        }
        else if (err_code != NRF_SUCCESS)
        {
            NRF_LOG_ERROR("sd_ble_gatts_hvx() failed: 0x%x", err_code);
        }

        p_ctx->bytes_sent += payload_len;

        if (p_ctx->kbytes_sent != (p_ctx->bytes_sent / 1024))
        {
            p_ctx->kbytes_sent = (p_ctx->bytes_sent / 1024);

            evt.evt_type             = NRF_BLE_AMTS_EVT_PACKET_244B;
            evt.bytes_transfered_cnt = p_ctx->bytes_sent;
            p_ctx->evt_handler(evt);
        }
    }
}

then in amt.h I added NRF_BLE_AMTS_EVT_PACKET_244B:

typedef enum
{
    NRF_BLE_AMTS_EVT_NOTIF_ENABLED,
    NRF_BLE_AMTS_EVT_NOTIF_DISABLED,
    NRF_BLE_AMTS_EVT_TRANSFER_1KB,
    NRF_BLE_AMTS_EVT_PACKET_244B,
    NRF_BLE_AMTS_EVT_TRANSFER_FINISHED,
} nrf_ble_amts_evt_type_t;

so in the main I used NRF_BLE_AMTS_EVT_PACKET_244B instead of NRF_BLE_AMTS_EVT_PACKET_1KB:

case NRF_BLE_AMTS_EVT_PACKET_244B:   
        {
            NRF_LOG_INFO("Packet sent");
            bsp_board_led_on(PROGRESS_LED);
            nrf_delay_ms(0.5);
            bsp_board_led_off(PROGRESS_LED);
        } break;

So I did this modifications to trigger the case NRF_BLE_AMTS_EVT_PACKET_244B each 244B instead of 1KB, blinking one of the led on the board. 

What I noticed is that if I send at least 4 packets (so AMT_BYTE_TRANSFER_CNT >= 244*4) it's ok, but if I send less than 4 packets from the terminal I see that I receive however 4 packets. For example, if I set AMT_BYTE_TRANSFER_CNT = 244*2, that's what I see on PuTTY terminal: 

Central:

as you see "Sent 976 bytes of ATT payload" which are 244*4, meanwhile on the peripheral happen the same:

May you can say me, since I did some modifications, if I should manage something else?

Thanks.

[Simonr]

Hi

Terje is out of office so I have taken over this case. Sorry about the late reply. 

I think Terje refers to when going from kBytes to Bytes, so the math you report here doesn't really add up correctly, since there are 1024 bytes in one kilobyte. 

Anyways, what you want here is to print out or see the data you're sending in order to review it, correct? The easiest would be to use a Bluetooth sniffer to sniff the data going over the air if you want to review it afterwards. Either with a dedicated sniffer or the nRF Sniffer with Wireshark. Another option would be to do it in the firmware of course, and for that you can use the object transfer service for reference I think. https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v15.3.0%2Fble_sdk_app_ots.html 

Best regards,

Simon

[Ste_]

Hi, I actually solved this part. Now I'm dedicating to the SPI part: I would connect the server board to an SPI Driver so the SPI Driver communicate to the server the bytes to send via BLE to the client. DO you have some Q&A to advise me?

Thanks