ble_app_att_mtu_throughput in details

Question

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.