Allwinner R128 BLE maximum throughput test correct configuration test

aleksib

Allwinner R128 BLE maximum throughput test correct configuration test [Copy link]

 

Before using R128, we need to understand the maximum throughput of BLE to facilitate the evaluation of the development of related functions. First, let's understand what factors affect the throughput of Bluetooth: **1. Bluetooth version and PHY:** The version and physical layer (PHY) of the Bluetooth device have a great impact on the throughput. For example, the R128 device supports Bluetooth 5.0, and Bluetooth 5.0 supports 2M PHY. Using 2M PHY will get higher data throughput. **2. DLE (Data Length Extension):** After Bluetooth version 4.2, BLE (Bluetooth Low Energy) began to support DLE (also known as long packets). Using long packets can make the payload of a single BLE data packet reach 251 bytes. Usually, this feature is enabled by default, which helps to improve data throughput. **3. MTU and data transmission volume:** The protocol stipulates that the maximum payload of LL data PDU is 251 bytes, that is, 251 bytes of L2CAP data can be transmitted at a time. There is a 4-byte header above the L2CAP Data, so the L2CAP Payload is 251-4=247 bytes, which means that 247 bytes of ATT data can be transmitted at a time. There is a 3-byte header above the ATT Data, so the ATT payload is 247-3=244 bytes, which means that 244 bytes of application data can be transmitted at a time. MTU (Maximum Transmission Unit) usually refers to the L2CAP Payload, that is, ATT data, which is 247 bytes in size. When sending data, the process of unpacking and assembling packets should be minimized to improve throughput. This means that when sending data, the application should try to send no more than 244 bytes of data each time.  **4. Connection interval:** BLE technology is characterized by low power consumption, which is mainly because the two BLE devices are not connected in the traditional sense, but interact periodically at intervals. This periodic interval is called the connection interval. The smaller the connection interval, the more data packets can be sent per unit time. Therefore, in order to improve throughput, the connection interval should be minimized.  **5. Maximum number of data packets per connection event:** During the Bluetooth connection process, the number of data packets that can be sent in each connection event is usually 7. If too many data packets are sent in a connection event, the throughput may decrease. Therefore, we should try to ensure that no more than 7 data packets are sent in a connection event. **6. Write operation:** In Bluetooth communication, write and write_without_response, indicate and notify are common operation modes. The write operation requires confirmation from the other party and is relatively inefficient; while write_without_response and notify operations do not require confirmation from the other party and are more efficient. Therefore, in order to improve throughput, write_without_response and notify operations should be used first. **Based on the above factors, we can develop a correct configuration that can meet the maximum throughput requirements** **1. Use 2M PHY** (1) If we act as GATTC, we should initiate the PHY UPDATE action. It has been adapted in the newer btmanager (only available after SDK V0.9), but not in the old version. If the customer does not use btmanager, he needs to check the adaptation by himself. (2) If we act as GATTS, generally mobile devices that support Bluetooth 5.0 have the PHY UPDATE action by default. **2. Update LL data length** Although the long packet function is supported by default, in order to be compatible with versions 4.0 and 4.1, the Bluetooth controller still uses 27-byte packets by default. It is necessary to actively update the LL data length to 251 bytes when connecting. It has been adapted in the newer btmanager (only available after SDK V0.9). If the customer does not use btmanager, he needs to check and adapt it by himself. **3. MTU and data transmission volume** L2CAP MTU is set to 247: ``` -CONFIG_BT_L2CAP_RX_MTU=65 +CONFIG_BT_L2CAP_RX_MTU=247 -CONFIG_BT_L2CAP_TX_MTU=65 +CONFIG_BT_L2CAP_TX_MTU=247 ``` At the same time, when sending data, the application or test demo should send a maximum of 244 bytes each time. **4. Connection interval** The connection interval range is 7.5ms ~ 4s. But it is not the case that the smaller the connection interval, the worse the anti-interference ability. * If the Bluetooth controller can send 7 data packets in one connection event, the connection interval should be set to be greater than 12.5ms, because these 7 packets have occupied about 9.5ms. * It is recommended to try the connection interval between 12.5ms, 13.75ms, and 15ms. (1) If we are acting as GATTC, we can specify it as the connection interval in btmg_le_connect. (2) If I use it as GATTS, and the connection interval used by the other party is too large, I can actively update it through the protocol stack. Related configurations ``` -# CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS is not set +CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS=y +CONFIG_BT_PERIPHERAL_PREF_MIN_INT=11 +CONFIG_BT_PERIPHERAL_PREF_MAX_INT=11 +CONFIG_BT_PERIPHERAL_PREF_SLAVE_LATENCY=0 +CONFIG_BT_PERIPHERAL_PREF_TIMEOUT=42 ``` **5. Increase the protocol stack TX and RX buff** Increasing the protocol stack TX buff allows data to be sent to the Bluetooth controller quickly. ``` -CONFIG_BT_CONN_TX_MAX=3 +CONFIG_BT_CONN_TX_MAX=8 -CONFIG_BT_L2CAP_TX_BUF_COUNT=3 +CONFIG_BT_L2CAP_TX_BUF_COUNT=8 ``` Increasing RX buff can improve receiving efficiency: It is set to 255 because it contains 4 bytes of HCI packet header. ``` -CONFIG_BT_RX_BUF_LEN=88 +CONFIG_BT_RX_BUF_LEN=255 -CONFIG_BT_DISCARDABLE_BUF_SIZE=88 +CONFIG_BT_DISCARDABLE_BUF_SIZE=255 ``` **6. Use write_without_response and notify to send data**

wang12011201

After Bluetooth 4.2, BLE (Bluetooth Low Energy) began to support DLE (also known as long packets), which can make the payload of a single BLE data packet reach 251 bytes. Usually, this feature is enabled by default, which helps to improve data throughput.