S132: What effect does is_var_len have in the softdevice?

[jcormier]

The documentation simply says: 1 for variable length and 0 for fixed length.

What exactly does changing this do? Do I save space by setting it to fixed? Why does BDS set it to 1 by default.

[Sigurd]

Hi,

is_var_len indicates if the user characteristic descriptor has variable length or not. When you are setting up characteristics there is a vlen field can be set to mark a characteristic as variable length. A characteristic can either be of constant length (vlen = 0), or of variable length (vlen = 1).

E.g. for the UART characteristics, it makes sense to have vlen = 1, since you may want to transmit any size of data from e.g. 1 to 20 bytes. But, e.g. for the Temperature Type, which is a fixed length characteristic (it has 8 bits and every bit is fixed),vlen should be 0.

[jcormier]

Thanks for the description.

Does this have an effect on characteristics used for notification throughput?