MRF24XA_15 Datasheet, PDF (178/258 Pages) Microchip Technology – Low-Power, 2.4 GHz ISM-Band IEEE 802.15.4™ RF

MRF24XA
6.7 Security Procedure for Proprietary
Frames
Provided that SecEn is set (1) in the MHR, three levels
of security processing are possible, based on the
SecLayer<1:0> bits carried in the AuxSecHdr<1:0>
field of a given frame: 00-MAC only, 01-NWK only,
10-MAC and NWK.
TABLE 6-6: SECURED FRAME TRANSMISSION (PROPRIETARY MAC FORMAT)
#
Processing Step
Steps per each Security Case
MAC only
NWK only
MAC + NWK layer
1 Host MCU constructs the frame and loads the buffer.
2 For NWK security processing, Host MCU configures:
SecEn = 1
No NWK layer
security
3 Host MCU triggers security processing without sending.
4 Device performs the security processing for NWKlayer if
TXENC is set.
SECPAYINDX, SECHDRINDX are filled in from NetHdrIn-
dex, NetPayIndex, respectively. SECENDINDX initially
points at the last payload byte.
LENGTH and SECENDINDX are updated if MIC tag is
appended. TXSZIF if size runs over 127 bytes.
5 Host MCU awaits TXENCIF interrupt, indicating
completion. Device clears TXENC.
SecEn = 1
SECKEY
SECSUITE
NONCE
No TXENC.
SecEn = 1
SECKEY
SECSUITE
NONCE
Host: TXENC ← 1
NWK layer
security
SECPAYINDX
SECHDRINDX
LENGTH,
SECENDINDX
TXENCIF ←1
TXENC ← 0
6 For MAC security processing, Host MCU configures:
SECKEY
SECSUITE
NONCE
No MAC security.
SECKEY
SECSUITE
NONCE
7 Host MCU triggers Security processing and sending.
8 If SecEn = 1 and DTSM = 0 then the device config-
ures the SEC*INDX registers using MacPayIndex,
MacHdrIndex and the LENGTH field.
Host: TXST ←1
SECHDRINDX
SECPAYINDX
SECENDINDX
Host: TXST ←1
—
Host: TXST ←1
SECHDRINDX
SECPAYINDX
SECENDINDX
9 Device performs the security processing for the indicated
layer:
LENGTH is adjusted if MAC or NWK layer MIC tag is
appended. TXSZIF if size run over 127 bytes.
MAC layer
security
LENGTH if MIC
added
NWK layer
security
LENGTH if MIC
added
MAC layer
security
LENGTH if MIC
added
10 LENGTH is adjusted as CRC is appended (if CRCSZ = 1).
TXSZIF if size run over 127 bytes.
LENGTH, CRC
11 Frame is sent.
TXIF (if no TXSZIF or FRMIF)
TXST ← 0
DS70005023B-page 178
Preliminary
 2015 Microchip Technology Inc.