Hello
I am developing an application where the data troughput is very important. As i understand, the data thoughput is dependent on the connection interval and the number of packets sent at every connection interval.
I am only able to get one packet sent at every connection interval. This means that throughput is not optimal as i must wait an entire connection interval before i can send the next packet. ( totaltime = scaninterval * packets )
My application is build on the SDK11.0.0 with SoftDevice 130, it supports 1 Central Link and 1 Peripheral Link.
Connection interval is set to min 15 max 20. (Slave Latency 0 and supervision timeout : 4s)
When acting as a central and sending 100bytes(100/20 = 5 packets) to peripheral i am doing it this way:
write_params.write_op = BLE_GATT_OP_WRITE_CMD;
write_params.offset = 0;
write_params.len = length;
write_params.p_value = buffer;
uint32_t errorCode = sd_ble_gattc_write(connectionHandle, &write_params);
Looping untill the errorcode is == BLE_ERROR_NO_TX_PACKETS
It works just fine, but when i snif the connection it looks like this:
As you can see every packet is sent in each connection interval. Which means that sending 100 bytes takes approx 67ms.
In my demo application the 100 bytes is sent back to the central when the entire buffer is received. When the peripheral is responding using the Notification Handle value i am doing pretty much the same:
hvx_params.p_data = buffer;
hvx_params.p_len = &length;
hvx_params.type = BLE_GATT_HVX_NOTIFICATION;
uint32_t errorCode = sd_ble_gatts_hvx(connectionHandle, &hvx_params);
Looping until errorCode == BLE_ERROR_NO_TX_PACKETS.
This gives a simular result on the snif output :
Meaning that it takes approx 70ms to deliver 100bytes.
When using an Android Device (LG Nexus 5, with 6.0.1) as central it is running even slower. (But it seems lie the android device is using a bigger connection interval)
When i look into this punchthrough.com/.../maximizing-ble-throughput-on-ios-and-android
It seems that Android devices should be able to send 4-6 packet pr connection interval. Giving an thoughput of up to 16Kbytes / second. However my thoughput is approx (100 bytes takes 67ms. (1000ms/67ms)*100bytes) = 1400KB/s
So i guess my questions are:
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Can i do anything to speed things up on the peripheral, and how?
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Can i do anything to speed things up on the central, and how?
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Can i do anything to speed things up on the android central, and how?
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What kind of thoughput can i expect?
Additional info:
During development and testing this application i am using the PCA10028 Dev Board(N51422 QFACA1), but the final result is supposed to run on a N51822 QFACA1 chip.
The peripheral in the example is Nordics PCA10000 dongle(N51822QFAAG0) Using SDK9.0.0 with SoftDevice 110. However when using the PCA10028 as peripheral it is the same thing.
I have attached some snif outputs
Android to Dongle: android_to_pca1000dongle.pcapng
