14.3.2 Frame Filter

Frame Filtering is a procedure that evaluates whether or not a received frame matches predefined criteria, like source or destination address or frame types. A filtering procedure as described in IEEE 802.15.4-2006 Section 7.5.6.2 (Third level of filtering) is applied to the frame to accept a received frame and to generate the address match interrupt IRQ_5 (AMI).

The AT86RF212B Frame Filter passes only frames that satisfy all of the following requirements/rules (quote from IEEE 802.15.4-2006, Section 7.5.6.2):

  1. The Frame Type subfield shall not contain a reserved frame type.
  2. The Frame Version subfield shall not contain a reserved value.
  3. If a destination PAN identifier is included in the frame, it shall match macPANId or shall be the broadcast PAN identifier (0xFFFF).
  4. If a short destination address is included in the frame, it shall match either macShortAddress or the broadcast address (0xFFFF). Otherwise, if an extended destination address is included in the frame, it shall match aExtendedAddress.
  5. If the frame type indicates that the frame is a beacon frame, the source PAN identifier shall match macPANId unless macPANId is equal to 0xFFFF, in which case the beacon frame shall be accepted regardless of the source PAN identifier.
  6. If only source addressing fields are included in a data or MAC command frame, the frame shall be accepted only if the device is the PAN coordinator and the source PAN identifier matches macPANId.

In addition the AT86RF212B has two additional requirements:

  1. The frame type shall indicate that the frame is not an acknowledgment (ACK) frame.
  2. At least one address field must be present.

Address match, indicated by interrupt IRQ_5 (AMI), is further controlled by the content of subfields of the frame control field of a received frame according to the following rule:

If Destination Addressing Mode is 0/1 and Source Addressing Mode is zero, no interrupt IRQ_5 (AMI) is generated. This effectively causes all acknowledgement frames not to be announced, which would otherwise always pass the filter, regardless of whether they are intended for this device or not.

For backward compatibility to IEEE 802.15.4-2003 third level filter rule two (Frame Version) can be disabled by the AACK_FVN_MODE bits in the CSMA_SEED_1 register (CSMA_SEED_1.AACK_FVN_MODE).

Frame filtering is available in Extended and Basic Operating Mode. A frame that passes the Frame Filter generates the interrupt IRQ_5 (AMI) if not masked.

Note:
  1. Filter rule one is affected by the AACK_FLTR_RES_FT and AACK_UPLD_RES_FT bits in the XAH_CTRL_1 register (XAH_CTRL_1.AACK_FLTR_RES_FT and XAH_CTRL_1.AACK_UPLD_RES_FT).
  2. Filter rule two is affected by register bits CSMA_SEED_1.AACK_FVN_MODE.