Hi,
I've been experimenting with the Mesh SDK (v3.2) on nRF52832 boards. After doing some end-to-end latency experiments, I've come up with some questions associated with broadcast behavior. First, I'll try to summarize how I understand the behavior up until now:
In advertiser.c, the method advertiser_packet_send is called when an upper layer wants to broadcast something. Upon checking the advertiser being enabled and non-active, the method schedule_first_time is called. This method will reschedule the transmission after a random BACKOFF between 0 and the advertisement interval associated with the advertiser instance, is called.
Upon timeout, the method timeout_event is called, which checks if the radio is busy transmitting. If not, it checks if a packet is available for transmission and starts the transmission. Also, if the radio was busy transmitting or has now started the transmission of the next available packet, the method setup_next_timeout is called. This method reschedules the timer to timeout after the advertisement INTERVAL + a standardized random backoff between 0 - 10 ms. Upon timeout, the method timeout_event is called again and process repeats itself, until no packets are available anymore in the buffer.
However, the packet buffer is filled by calling advertiser_packet_send. In some cases, the method schedule_first_time is also called again in that method, even though an interval was already scheduled in setup_next_timeout. This happens for example, when relaying a packet. The method schedule_first_time then reschedules the timeout after the random BACKOFF and removes the scheduled interval timeout. In other cases, the method schedule_first_time is not called within advertiser_packet_send, because of the check for the advertiser being enabled and non-active fails. This is the case for example when scheduling retransmission's because of the configured retransmission count state in the transmitting model. This retransmission then does happen, but only after the previous configured INTERVAL.
Now for the questions:
- Does each advertiser have a separate packet buffer or queue? In other words, are relay packets queued separately opposed to originator packets?
- In what cases does calling advertiser_packet_send also mean that a previous configured INTERVAL by setup_next_timeout will be overwritten by novel RANDOM backoff configured by schedule_first_time being called again. In other words, when does the check for the advertiser being enabled and non-active, succeed?
Thanks!
Kind regards,
Mathias
