I want to connect a Raspberry Pi to a handheld ARM MCU-based device which contains a display and some buttons to show information from the Pi and transmit commands. I want to use nrf24l01+ 2.4GHz transceivers for that.
I'm pondering with how to setup the communications link and especially whether or not to use Enhanced Shock Burst (ESB). ESB is very practical since it supports auto-ack and hence could relieve me of manual ack-management which is a hassle especially on the MCU-based device. However, from how much I have understood from the datasheets, ESB requires one device to be a primary receiver and one device to be a primary transmitter and only the latter initiates a new transmission, even though the former can transmit data in it's reponse. In my case, this is problematic because both devices receive external events that trigger the need for a data transmission.
I've been reading around and there is basically three possible solutions to this problem:
Configure one device as PTX and one as PRX and have the PTX send empty messages to give the PRX a chance to send it's data in a response packet. This seems to be done by some projects. I see the downside of continuously having traffic on the air which is bad for battery powered devices. Furthermore, the PRX still needs some buffer to store the messages until a transmission comes in and the message can be sent in the acknowledgement.
Configure both devices as PRX. If one device needs to transmit a message it switches to PTX role and transmits the message. The advantage is that there is no continuous traffic on the air and both devices can transmit the messages as needed. However, I didn't find that this is being done anywhere. So I wonder if this is possible or if there are other caveats with this solution?
Ditch Enhanced Shock Burst and make an own protocol. The least favored solution as it involves more work and puts more load on the controller. The automatic retransmit feature sounds very good and it would be a shame to put this potential to waste.
So I wonder if anyone had this problem already and how you solved it. I would especially like to know if there are problems with possibility two.