Hi @hek ,

I don't get why you would need 254*32 bytes. Actually, only the memory for pending messages are required. When the GW received from a node, it just has to scan in its pending messages list for a matching node, and send the message (then remove from the list).

Because of limited memory constraint, you'll not be able to have a single message per node at a time, but since only few nodes are actuators, I think it should not be an issue.

I've code around doing this, unfortunately not for MySensor (I found your project only recently). I'll try to create a PR for it, if you don't mind.

@tbowmo Each packages would use a single message. Here, the idea is that a single message of 32 bytes does not take more power to send than a message of 12 bytes (what's power hungry is waking up the radio, transmitting a burst). For battery powered device, it makes a difference

@hek The main use case I see (and for me it's a must have) is for power saving. Typically, I've a motion sensor + temp/hum in a single node.
The motion sensor is not active (it's OFF electrically) when the home is not activated.

When I activate the home, the gateway sends all motion sensors' node the order to switch on. But since the nodes are sleeping 99.99% of the time, without a mailbox, these messages would be lost, resulting in the home not activated.

However, if the gateway stores at least one pending message, then, when the node wakes up to send its periodic message, the gateway tells it not to sleep immediately, and sends the pending message back to the node. This, in turns, switches the motion sensor ON.

My sleep time is 8s, so I know that when the home is under alarm, at worst, 8s later the motion sensor is running.

In fact for any actuator (not sensor), this is absolutely required when battery powered.

S_COMBO/V_COMBO new mode in order to merge multiple sensors value in a single message
The basic structure should be like this:

When type is S_COMBO/V_COMBO, the payload is made with multiple (uint8 variable-type, uint8 data[]) tuple, up to 24 bytes.
For example, if you have a node that's temperature and humidity capable, it would send a message like this:

MyMessage msg(CHILD_ID, V_COMBO);
uint8 msgTemplate[] = { V_TEMP, 0, V_HUM, 0 };
[...]
msgTemplate[1] = readCurTemp(); msgTemplate[3] = readCurHum();
gw.send(msg.set(msgTemplate));

This would require almost no modification to the current software.
The main advantage is saving power, only a single packet is sent (instead of multiple packets for each sensor, plus ACK).
This limits however each type payload to one byte.
Another improvement would be to reuse the existing parsing code by adding a MyMessage.set/get method like this:

inline bool isCombo() const { return type == V_COMBO; }
MyMessage & setCombo(uint8_t pos, uint8_t type, uint8_t value) 
{ 
    data[pos*2] = type; data[pos*2+1] = value; 
    return *this; 
}

On the gateway, an additional case should be taken when serializing to/from Ethernet or Serial so it appears not like a combo.