What is frame, sample source in position x and limelight interface settings?


Hello @Zack
This is with reference to the terminology in the Programming guide and the connection to the waveforms in the datasheet.
There is the use of the word “Frame” which I am unable to trace.

  1. Reg 0x0023, LMLx_FIDM: frame start ID selection. What does this mean?

  2. Reg 0x0024, Sample source in positions 0,1,2,3. Where are these positions defined?
    Is the TRXIQPULSE mode same as JESD 207 mode?

  3. From the FPGA code I understood that there are four modes of operation of the limelight interface:
    1) SISO_DDR
    2) SISO_SDR
    3) MIMO_DDR
    4) PULSE_DDR
    Please advise on how are these configured.
    3.1) Register 0x0022, LMLx_SISODDR (DDR mode off/on). Does turning it OFF enable SISO_SDR mode ON?
    3.2) How is MIMO_DDR mode enabled (does turning OFF TRXIQPULSE mode off enable MIMO_DDR)?
    3.3) Could you please provide the waveform for SISO_DDR mode? My understanding is the following:
    Figs 33-36: are PULSE_DDR/JESD 207 mode
    Figs 37-38: are MIMO-DDR mode which is same as TRXIQ DDR mode
    Figs 39-40: are SISO-SDR mode

Thanks as always for your time and help,


Hi @EnthuMan,

It lets you know when new data frame starts. Actually, it defines ENABLE_IQ_SEL signal behavior. If LMLx_FIDM is set to 0, then ENABLE_IQ_SEL signal will be low when new data frame starts. For instance, let us assume LMS7 sends this sequence of IQ data:
AI0, AQ0, BI0, BQ0, AI1, AQ1, BI1, BQ1, …
If LMLx_FIDM is set to 0, then ENABLE_IQ_SEL will be low when AI0, AQ0 and AI1, AQ1 and high when BI0, BQ0 and BI1, BQ1
In the case above, it actually identifies MIMO A or MIMO B channel.

Assume IQ data frame from example above: AI0, AQ0, BI0, BQ0. Register 0x0024, bits [8:15] defines sample position in this sequence. If these are kept as default, then sequence will be AI, AQ, BI, BQ. If you set LML1_SxS[1:0] registers to 0, then frame will be as follows: AI, AI, AI, AI (not very useful, just as an example).
Another example. Let us set:
LML1_S0S[1:0] = 11
LML1_S1S[1:0] = 10
LML1_S2S[1:0] = 01
LML1_S3S[1:0] = 00
Then IQ data frame sequence will be: BQ, BI, AQ, AI.

No, it is more like TRXIQ. The difference is in ENABLE_IQ_SEL duration only. In TRXIQ mode ENABLE_IQ_SEL duration length is 2 samples, while in TRXIQPULSE mode ENABLE_IQ_SEL duration length is 1 sample.

Check this document for more information: