14.2.2 Extended Operationg Mode

Extended Operating Mode makes up for a large set of automated functionality add-ons which can be referred to as a hardware MAC accelerator. These add-ons go beyond the basic radio transceiver functionality provided by the Basic Operating Mode. Extended Operating Mode functions handle time critical MAC tasks, requested by the IEEE 802.15.4 standard, in hardware, such as automatic acknowledgement, automatic CSMA‑CA, and retransmission. This results in a more efficient IEEE 802.15.4 software MAC implementation, including reduced code size, and may allow use of a smaller microcontroller or operation at low clock rates.

The Extended Operating Mode is designed to support IEEE 802.15.4‑2006 and IEEE 802.15.4‑2011 compliant frames; the mode is backward compatible to IEEE 802.15.4‑2003 and supports non IEEE 802.15.4 compliant frames. This mode comprises the following procedures:

Automatic acknowledgement (RX_AACK) divides into the tasks:

  • Frame reception and automatic FCS check
  • Configurable addressing fields check
  • Interrupt indicating address match
  • Interrupt indicating frame reception, if it passes address filtering and FCS check
  • Automatic ACK frame transmission (if the received frame passed the address filter and FCS check and if an ACK is required by the frame type and ACK request)
  • Support of slotted acknowledgment using SLP_TR pin (used for beacon-enabled operation)

Automatic CSMA-CA and Retransmission (TX_ARET) divides into the tasks:

  • CSMA‑CA, including automatic CCA retry and random backoff
  • Frame transmission and automatic FCS field generation
  • Reception of ACK frame (if an ACK was requested)
  • Automatic retry of transmissions if ACK was expected but not received or accepted
  • Interrupt signaling with transaction status

Automatic FCS check and generation, refer to Section 8.3, is used by the RX_AACK and TX_ARET modes. In RX_AACK mode, an automatic FCS check is always performed for incoming frames.

In TX_ARET mode, an ACK which is received within the time required by IEEE 802.15.4 is automatically accepted if the FCS is valid and the ACK sequence number must match the sequence number of the previously transmitted frame. Dependent on the value of the frame pending subfield in the received acknowledgement frame received, the transaction status is set, see the TRAC_STATUS bits in the TRX_STATE register (TRX_STATE.TRAC_STATUS).

An AT86RF212B state diagram, including the Extended Operating Mode states, is shown in the figure below. Orange marked states represent the Basic Operating Mode; blue marked states represent the Extended Operating Mode.

Figure 14-26. Extended Operating Mode State Diagram