central_uart example, how to get Write Response packet?

Question

Hi, 
 NCS v2.6.0 
 nRF52 DK 
 central_uart send packet to peripheral_uart, then peripheral_uart send write response packet to central_uart. 
 How to get the write response packet in central_uart callback function? I have a large data to send from central_uart to peripheral_uart, 
 I want to send the first packet from central, then received the write response from peripheral to make sure the packet was received by peripheral, and then send the next packet from central. 
 
 There is a similar thread, but it doesn't answer my question. 
 Is there response from peripheral_uart after central_uart write rx characteristic

Edvin · Accepted Answer

Hello, 
 Just to clarify before digging into this. All packets are retransmitted until they are ACKed in Bluetooth Low Energy. So either the packet is ACKed, or the connection is lost. All packets (from peripheral and central) have a CRC, and if this is incorrect, then it will tell the other device to retransmit that packet. If no packets are received with the correct CRC within the connection supervision timeout period, the link is disconnected. 
 So the typical (and most effective, if you consider data throughput) is to just queue up as many packets as you can. What I used to say in the old SDK is to use the ACK event as a trigger to queue more packets. In the central_uart sample, this would be the ble_data_sent() callback in main.c. This is triggered from the on_sent() callback in nus_client.c, which is triggered when a packet is ACKed. You can even see the bt_gatt_write_params *params in the callback, to determine which packet that was acked. In turn, this is all triggered from the gatt_write_rsp() in gatt.c. 
 
 Best regards, 
 Edvin

central_uart example, how to get Write Response packet?

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