Interframe spacing (IFS)

Interframe spacing (IFS) is defined as the time in microseconds between two consecutive packets, starting from when the end of the last bit of the previous packet is received, to the beginning of the first bit of the subsequent packet that is transmitted.

RADIO can enforce this interval, as specified in the TIFS register, as long as the TIFS register is not specified to be shorter than the RADIO peripheral's turnaround time (meaning the time needed to switch off the receiver and then switch on the transmitter). The TIFS register can be written any time before the last bit on air is received.

This timing is illustrated in the following figure.

The TIFS duration starts after the last bit on air (at the PHYEND event), and elapses with the first bit being transmitted on air (just after READY event).

TIFS is only enforced if the shortcuts PHYEND to DISABLE and DISABLED to TXEN or PHYEND to DISABLE and DISABLED to RXEN are enabled. The short READY to START must also be enabled. In these configurations, TXEN or RXEN is automatically delayed to achieve the configured interframe spacing.

TIFS is qualified for use in IEEE 802.15.4 250kbps mode, Bluetooth Low Energy Long Range (125 kbps and 500 kbps) modes, and Bluetooth Low Energy 1 Mbps and 2 Mbps modes, using the Legacy ramp-up mode.

SHORTS and TIFS registers are not double-buffered and can be updated at any point before the last bit on air is received. The MODE register is double-buffered and sampled at the TXEN or RXEN task.