This section describes the processor availability and interrupt processing time for the SoftDevice in a central connection event.
In a central connection event, the pattern of SoftDevice processing activity at interrupt priority level 0 is typically as follows:
SoftDevice processing activity in the different priority levels during central connection events is outlined in Processor usage latency when connected. The typical case is seen when receiving GATT write commands writing 20 bytes. The max case can be seen when sending and receiving maximum length packets and initiating encryption, while having a maximum number of connections and utilizing the Radio Timeslot API, Flash memory API, using PA/LNA, and Quality of Service (QoS) channel survey module at the same time.
Parameter | Description | Min | Typical | Max |
---|---|---|---|---|
tISR(0),RadioPrepare |
Processing when preparing the radio for a connection event |
83 μs | 84 μs | |
tISR(0),RadioStart | Processing when starting the connection event | 18 μs | 18 μs | |
tISR(0),RadioProcessing | Processing after sending or receiving a packet | 98 μs | 102 μs | |
tISR(0),PostProcessing | Processing at the end of a connection event | 97 μs | 207 μs | |
tnISR(0) | Distance between connection event interrupts | 183 μs | > 200 μs | |
tISR(4) | Priority level 4 interrupt after a packet is sent or received | 40 μs |
From the table we can calculate a typical processing time for a central connection event where one packet is sent and received to be:
tISR(0),RadioPrepare
+
tISR(0),RadioStart
+
tISR(0),RadioProcessing
+
tISR(0),PostProcessing
+ 2 *
tISR(4)
=
376 μs
This means typically more than 99% of the processor time is available to the application when one central link is established and one packet is sent in each direction with a 100 ms connection interval.