Who owns a characteristic's value ?

[Thomas]

My system is a BLE peripheral with 2 states. There is a characteristic that represents the state, and it can take 2 values: 0 and 1. You can read the state, write it (force the system to change state), or be notified (be informed when system state changes).

I understood how to set the initial value, and my handler gets called when there is a write. But what happens if I write "0x02" to the characteristic ? my write handler won't do anything as the state is not valid, but the characteristic will take "2" as the value !! How do I prevent that ? In other words, how should I synchronize my internal state and the characteristic's value ?

I tried to use attr_md.vloc = BLE_GATTS_VLOC_USER; and I did attr_char_value.p_value = &my_internal_state but that doesn't seem to help. What should be the correct way ? Thanks

P.S Im using sdk 8.1

[MartinBL]

Hi

Maybe you can to a control check of the received value at the write event. You can read the value with e.g. p_ble_evt->evt.gatts_evt.params.write.data. If the value is '0' or '1' everything is good, but if it is something else you can do:

uint8_t your_state = 0x01;     // Your desired alternate state
ble_gatts_value_t value;       // Variable to hold desired state value with length and offset information
value.len = 1;                 // Lenght of your state characteristic
value.offset = 0;              // Offset of your state characteristic
value.p_value = &your_state;   // Alternate state
sd_ble_gatts_value_set("current connection handle", "characteristic handle", &value); // Write new state to characteristic

to overwrite the new value.

[Thomas]

this doesn't work. I did that in the on_write() method, of my ble service, just after calling my write_handler.

[Thomas]

your solution works when I used attr_md.vloc = BLE_GATTS_VLOC_STACK. thanks!

[Thomas]

I thought that vloc =... USER meant that I could give a pointer of my state to the characteristic, and the characteristic value would always point to my state. is it wrong ?