The RADIO uses DMA to write IQ samples recorded during the Constant Tone Extension (CTE) to RAM.
Alternatively, the magnitude and phase of the samples can be recorded using the DFECTRL1.SAMPLETYPE field. The samples are written to the location in RAM specified by DFEPACKET.PTR. The maximum number of samples to transfer are specified by DFEPACKET.MAXCNT and the number of samples transferred are given in DFEPACKET.AMOUNT.
MAXCNT is defined as number of words and must be determined from the length of the CTE and the sample intervals. This can be calculated as:
MAXCNT = 2*(8/TSAMPLESPACINGREF + (8*NUMBEROF8US-12)/TSAMPLESPACING)
For typical values of TSAMPLESPACINGREF and TSAMPLESPACING, this can be simplified as:
| TSAMPLESPACING | |||
| 2 µs | 4 µs | ||
| TSAMPLESPACINGREF | 0.5 µs | 20 + 8*NUMBEROF8US | 26 + 4*NUMBEROF8US |
| 1 µs | 4 + 8*NUMBEROF8US | 10 + 4*NUMBEROF8US | |