# HG changeset patch # User Mychaela Falconia # Date 1500331775 0 # Node ID 615df2fb1ec3f027a524194790c7b38e1430852f # Parent 037d9200aae4f8bd61d17398b507bb744f3a598c doc/Tx-cal-theory: update with both theory and practice diff -r 037d9200aae4 -r 615df2fb1ec3 doc/Tx-cal-theory --- a/doc/Tx-cal-theory Mon Jul 17 19:15:44 2017 +0000 +++ b/doc/Tx-cal-theory Mon Jul 17 22:49:35 2017 +0000 @@ -48,23 +48,109 @@ calibration basis run (because slot 0 is a valid power level for these bands), but an artifact remains in the levels.900 table in the unused slot 0. -In the present FreeCalypso RF calibration tools suite the planned -fc-rfcal-txband program that will perform the entire Tx band calibration -procedure has not been written yet. Instead we have the following two building -blocks: +Target power level numbers +========================== + +Ideally the power level numbers to be used as the targets for the calibration +process would be the levels given in the GSM 05.05 spec: from 33 dBm down to +5 dBm for the EGSM and GSM850 bands or from 30 dBm down to 0 dBm for DCS and +PCS, in 2 dBm steps in each case. However, the evidence from TI's calibration +documents (both Sara and LoCosto) is that some devices are not able to produce +the very highest and sometimes the very lowest power levels given in the spec, +and getting a successful calibration requires setting the calibration targets +to slightly shifted numbers, although still within the tolerances allowed by +the GSM 05.05 spec. The table in TI's Sara calibration document (page 26) has +the highest power level reduced by 1.2 relative to the spec, the next highest +by 0.5, whereas the lowest 4 (EGSM) or 6 (DCS) levels are raised and compacted +together. The table in the LoCosto document (page 44) has the highest power +level for each band reduced by 0.8, making it 32.2 dBm for EGSM and GSM850 and +29.2 dBm for DCS and PCS, while all other levels are set to the spec numbers. + +In my own experience with getting the Tx power levels calibrated on our current +FCDEV3B boards, our hardware is able to hit all of the lowest spec power levels +with good margin (the APC DAC value never goes below the 60-70 range), hence +the low targets did not need to be shifted, but the highest spec power level +could not be achieved in every band. Following TI's practice with LoCosto, I +set the highest power level target to 32.2 dBm for the EGSM band and to 29.2 dBm +for PCS, but I was consistently able to get the full 30 dBm out in the DCS band, +hence I set the DCS band highest power level target to the official number of +30 dBm. It needs to be emphasized, however, that these results are quite +specific to our current flock of FCDEV3B hardware, and your results will most +likely be different if you are working with a different hw design such as a +non-FreeCalypso derivative of Openmoko's GTA02 design. + +Profiles for Tx levels calibration +================================== + +Our fc-rfcal-txband program that performs the actual per-unit calibration of Tx +power levels for each band requires a preconfigured txlevels calibration profile +for each band as one of its inputs; if you are performing calibration on +individual units of a board design for which the correct profiles have already +been crafted, you simply use those given profiles (fcom1 for our current flock +of FCDEV3B boards), but if you are doing Tx power level calibration on a new +board design for the first time, you first need to characterize the Tx output +level behaviour of your new board design and craft the appropriate set of +profiles. -fc-rfcal-txbasis performs the preliminary "basis" step of Tx power level -calibration: it sets the APC DAC to each of the values given on the command line -in turn, and reports the resulting output power level in dBm. The temporary -APC DAC values do get written into the Tx levels table in L1 (there is no other -way to set the APC DAC value for the active transmitter through Test Mode), but -the MISC_ENABLE command to save Tx calibration tables in FFS is NOT issued, -thus the corruption of the Tx levels table inflicted by this program will get -blown away on the next rfpw 7 (Test Mode band selection) command. +The profiles for txlevels calibration reside in /opt/freecalypso/rfcal/txlevels; +each per-band profile is sought in a file named profile_name-band_number, where +profile_name is the profile name argument given to fc-rfcal-txband and +band_number is one of 850, 900, 1800 or 1900. For example, the profile set for +our current FCDEV3B hardware is named fcom1 ("FreeCalypso hardware, Openmoko- +based, version 1"), this hw platform is 900/1800/1900 MHz triband, and the +individual profile config files are fcom1-900, fcom1-1800 and fcom1-1900. + +Each profile provides two key pieces of data: the list of fixed APC DAC values +to be used as the basis set for constructing the piecewise linear model, and +the list of power levels in dBm that will be the targets for the calibration. + +Crafting the txlevels calibration profiles for a new board design +================================================================= + +If you are working with a new (or new-to-you) board design with no previous Tx +levels calibration experience, you need to begin by characterizing its Tx +output level behaviour so you can determine what APC values are appropriate for +the basis set, whether or not you need to shift the highest and/or lowest +target levels from their nominal spec values, and if some target shifting is +needed, which levels need to be shifted and by how much. + +The tool you will need for this investigation is fc-rfcal-txbasis. It requires +fc-cmu200d and rvinterf to be running, talking to the CMU200 and to the DUT, +respectively, and it takes the band number (850/900/1800/1900) and a set of +APC DAC values on the command line; no pre-existing txlevels profile is needed. +It commands the DUT to transmit at each of the specified APC DAC values in turn +and reports the power output levels measured by the CMU200. + +VERY IMPORTANT: You need to be very sure that your CMU200 or other measuring +instrument is itself in good calibration standing, i.e., that the measurements +it reports are trustworthy, and that the insertion loss in your cabling setup +(all the way from the actual DUT's antenna connector or RF test port to your +CMU200) really matches the numbers you have put in your cable configuration file +(see Cable-config-howto). If you fail to ensure these prerequisites, your +fc-rfcal-txbasis observations will be meaningless, as the cable insertion losses +are typically of the same order of magnitude as the transmitter differences you +are trying to determine. + +You will need to run fc-rfcal-txbasis with a guesstimated set of APC DAC values, +to be revised iteratively, and get a feel for what your DUT is putting out. +Are you able to hit the lowest spec power level consistently while the APC DAC +value remains well above zero? Are you able to hit the highest spec power level +as well, or does the measured power output fall short of this target no matter +how high you crank the APC DAC? These observations will tell you whether or not +you need to shift the highest and/or lowest target power levels in your new +txlevels calibration profile. + +Regular calibration runs +======================== + +Once you have a good set of profiles for the type of Calypso GSM device you are +calibrating, just run fc-rfcal-txband with the band number and the name of your +profile. + +Checking existing calibration +============================= fc-rfcal-txcheck is a completely non-invasive program (does not make any writes to any L1 RF tables or to FFS) that steps through all power levels for the specified band (5-19 for EGSM or GSM850, or 0-15 for DCS or PCS), performs a -power measurement at each level, and displays the measured result. An -equivalent operation will be the finishing sanity check step in the full Tx -power level calibration program. +power measurement at each level, and displays the measured result.