Source Address Matching - Texas Instruments CC253x User Manual

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• Keep the bit cleared otherwise.
It is not necessary to turn off the receiver while changing the values of the FRMFILT0 and FRMFILT1
registers and the local address information stored in RAM. However, if the changes take place between
reception of the SFD byte and the source PAN ID (that is, between the SFD and RX_FRM_ACCEPTED
exceptions), the modified values must be considered as don't care for that particular frame (the radio uses
either the old or the new value).
Note that it is possible to make the radio ignore all IEEE 802.15.4 incoming frames by setting
MDMTEST1.MODULATION_MODE = 1.

23.9.6 Source Address Matching

The radio supports matching of the source address in received frames against a table stored in the on-
chip memory. The table is 96 bytes long, and hence it can contain up to:
• 24 short addresses (2-byte PAN ID + 2-byte short address).
• 12 IEEE extended addresses (8 bytes each).
Source address matching is only performed when frame filtering is also enabled and the received frame
has been accepted. The function is controlled by:
• The SRCMATCH, SRCSHORTEN0, SRCSHORTEN1, SRCSHORTEN2, SRCEXTEN0, SRCEXTEN1, and
SRCEXTEN2 registers
• The source address table in RAM
Applications
Automatic acknowledgment transmission with correct setting of the frame-pending bit: When using indirect
frame transmission, the devices send data requests to poll frames stored on the coordinator. To indicate
whether it actually has a frame stored for the device, the coordinator must set or clear the frame-pending
bit in the returned acknowledgment frame. On most 8- and 16-bit MCUs, however, there is not enough
time to determine this, and so the coordinator ends up setting the pending bit regardless of whether there
are pending frames for the device (as required by IEEE 802.15.4 [1]). This is wasteful in terms of power
consumption, because the polling device must keep its receiver enabled for a considerable period of time,
even if there are no frames for it. By loading the destination addresses in the indirect frame queue into the
source address table and enabling the AUTOPEND function, the radio sets the pending bit in outgoing
acknowledgment frames automatically. This way, the operation is no longer timing-critical, as the effort
done by the microcontroller is when adding or removing frames in the indirect frame queue and updating
the source address table accordingly.
Security material look-up: To reduce the time needed to process secured frames, the source address
table can be set up so the entries match the table of security keys on the CPU. A second level of masking
on the table entries allows this application to be combined with automatic setting of the pending bit in
acknowledgment frames.
Other applications: The two previous applications are the main targets for the source-address matching
function. However, for proprietary protocols that only rely on the basic IEEE 802.15.4 frame format, there
are several other useful applications. For instance, it is possible to create firewall functionality where only
a specified set of nodes is to be acknowledged.
The Source Address Table
The source address table begins at address 0x6100 in RAM. The space is shared between short and
extended addresses, and the SRCSHORTEN0, SRCSHORTEN1,
SRCSHORTEN2 and SRCEXTEN0, SRCEXTEN1,
SRCEXTEN2 registers are used to control which entries are enabled. All values in the table
are little-endian (as in the received frames).
• A short address entry starts with the 16-bit PAN ID followed by the 16-bit short address. These entries
are stored at address 0x6100 + (4 × n), where n is a number between 0 and 23.
• An extended address entry consists only of the 64-bit IEEE extended address. These entries are
stored at address 0x6100 + (8 × n), where n is a number between 0 and 11.
Address Enable Registers
Software is responsible for allocating table entries and for making sure that active short and extended
address entries do not overlap. There are separate enable bits for short and extended addresses:
SWRU191F – April 2009 – Revised April 2014
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