Random-Number Generation; Fft Of The Random Bytes; Fsm State Mapping - Texas Instruments CC253x User Manual

Random-Number Generation

Table 23-3 shows the mapping from FSM state to the number which can be read from the FSMSTAT0
register. Note that although it is possible to read the state of the FSM, this information should not be used
to control the program flow in the application software. The states may change very quickly (every 32-MHz
clock cycle), and an 8-MHz SPI is not able to capture all the activities.
State Name
Idle
RX calibration
SFD wait
RX
TX or RX wait
RXFIFO reset
RX overflow
TX calibration
TX
TX final
TX or RX transit
ACK calibration
ACK
ACK delay
TX underflow
TX shutdown
23.12 Random-Number Generation
The RF Core can generate random bits. The chip should be in RX when generation of random bits is
required. One must also make sure that the chip has been in RX long enough for the transients to have
died out. A convenient way to do this is to wait for the RSSI-valid signal to go high.
Single random bits from either the I or Q channel can be read from the register RFRND.
Randomness tests show good results for this module. However, a slight dc component exists. In a simple
test where the RFRND.IRND register was read a number of times and the data grouped into bytes, about
20 million bytes were read. When interpreted as unsigned integers between 0 and 255, the mean value
was 127.6518, which indicates that there is a dc component.
The FFT of the first 2
histogram (32 bins) of the 20 million values is shown in
236
CC253x Radio
Table 23-3. FSM State Mapping
State Number, Decimal
0
2
3–6
7–13
14
16
17
32
34–38
39
40
48
49–54
55
56
26, 57
14
bytes is shown in Figure
Copyright © 2009–2014, Texas Instruments Incorporated
Number, Hex TX_ACTIVE
0x00 0
0x02 0
0x03–0x06 0
0x07–0x0D 0
0x0E 0
0x10 0
0x11 0
0x20 1
0x22–0x26 1
0x27 1
0x28 1
0x30 1
0x31–0x36 1
0x37 1
0x38 1
0x1A, 0x39 1
23-21. Note that the dc component is clearly visible. A
Figure 23-22.
SWRU191F – April 2009 – Revised April 2014
www.ti.com
RX_ACTIVE
0
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
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