FreeCalypso > hg > fc-rfcal-tools
comparison doc/Tx-cal-theory @ 98:615df2fb1ec3
doc/Tx-cal-theory: update with both theory and practice
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 17 Jul 2017 22:49:35 +0000 |
parents | 8e675142cca7 |
children | 16aab86384a7 |
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97:037d9200aae4 | 98:615df2fb1ec3 |
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46 written into Tx levels table slots 5-19 for EGSM and GSM850, or 0-15 for DCS | 46 written into Tx levels table slots 5-19 for EGSM and GSM850, or 0-15 for DCS |
47 and PCS. In the case of DCS and PCS no visible artifacts remain from the | 47 and PCS. In the case of DCS and PCS no visible artifacts remain from the |
48 calibration basis run (because slot 0 is a valid power level for these bands), | 48 calibration basis run (because slot 0 is a valid power level for these bands), |
49 but an artifact remains in the levels.900 table in the unused slot 0. | 49 but an artifact remains in the levels.900 table in the unused slot 0. |
50 | 50 |
51 In the present FreeCalypso RF calibration tools suite the planned | 51 Target power level numbers |
52 fc-rfcal-txband program that will perform the entire Tx band calibration | 52 ========================== |
53 procedure has not been written yet. Instead we have the following two building | |
54 blocks: | |
55 | 53 |
56 fc-rfcal-txbasis performs the preliminary "basis" step of Tx power level | 54 Ideally the power level numbers to be used as the targets for the calibration |
57 calibration: it sets the APC DAC to each of the values given on the command line | 55 process would be the levels given in the GSM 05.05 spec: from 33 dBm down to |
58 in turn, and reports the resulting output power level in dBm. The temporary | 56 5 dBm for the EGSM and GSM850 bands or from 30 dBm down to 0 dBm for DCS and |
59 APC DAC values do get written into the Tx levels table in L1 (there is no other | 57 PCS, in 2 dBm steps in each case. However, the evidence from TI's calibration |
60 way to set the APC DAC value for the active transmitter through Test Mode), but | 58 documents (both Sara and LoCosto) is that some devices are not able to produce |
61 the MISC_ENABLE command to save Tx calibration tables in FFS is NOT issued, | 59 the very highest and sometimes the very lowest power levels given in the spec, |
62 thus the corruption of the Tx levels table inflicted by this program will get | 60 and getting a successful calibration requires setting the calibration targets |
63 blown away on the next rfpw 7 (Test Mode band selection) command. | 61 to slightly shifted numbers, although still within the tolerances allowed by |
62 the GSM 05.05 spec. The table in TI's Sara calibration document (page 26) has | |
63 the highest power level reduced by 1.2 relative to the spec, the next highest | |
64 by 0.5, whereas the lowest 4 (EGSM) or 6 (DCS) levels are raised and compacted | |
65 together. The table in the LoCosto document (page 44) has the highest power | |
66 level for each band reduced by 0.8, making it 32.2 dBm for EGSM and GSM850 and | |
67 29.2 dBm for DCS and PCS, while all other levels are set to the spec numbers. | |
68 | |
69 In my own experience with getting the Tx power levels calibrated on our current | |
70 FCDEV3B boards, our hardware is able to hit all of the lowest spec power levels | |
71 with good margin (the APC DAC value never goes below the 60-70 range), hence | |
72 the low targets did not need to be shifted, but the highest spec power level | |
73 could not be achieved in every band. Following TI's practice with LoCosto, I | |
74 set the highest power level target to 32.2 dBm for the EGSM band and to 29.2 dBm | |
75 for PCS, but I was consistently able to get the full 30 dBm out in the DCS band, | |
76 hence I set the DCS band highest power level target to the official number of | |
77 30 dBm. It needs to be emphasized, however, that these results are quite | |
78 specific to our current flock of FCDEV3B hardware, and your results will most | |
79 likely be different if you are working with a different hw design such as a | |
80 non-FreeCalypso derivative of Openmoko's GTA02 design. | |
81 | |
82 Profiles for Tx levels calibration | |
83 ================================== | |
84 | |
85 Our fc-rfcal-txband program that performs the actual per-unit calibration of Tx | |
86 power levels for each band requires a preconfigured txlevels calibration profile | |
87 for each band as one of its inputs; if you are performing calibration on | |
88 individual units of a board design for which the correct profiles have already | |
89 been crafted, you simply use those given profiles (fcom1 for our current flock | |
90 of FCDEV3B boards), but if you are doing Tx power level calibration on a new | |
91 board design for the first time, you first need to characterize the Tx output | |
92 level behaviour of your new board design and craft the appropriate set of | |
93 profiles. | |
94 | |
95 The profiles for txlevels calibration reside in /opt/freecalypso/rfcal/txlevels; | |
96 each per-band profile is sought in a file named profile_name-band_number, where | |
97 profile_name is the profile name argument given to fc-rfcal-txband and | |
98 band_number is one of 850, 900, 1800 or 1900. For example, the profile set for | |
99 our current FCDEV3B hardware is named fcom1 ("FreeCalypso hardware, Openmoko- | |
100 based, version 1"), this hw platform is 900/1800/1900 MHz triband, and the | |
101 individual profile config files are fcom1-900, fcom1-1800 and fcom1-1900. | |
102 | |
103 Each profile provides two key pieces of data: the list of fixed APC DAC values | |
104 to be used as the basis set for constructing the piecewise linear model, and | |
105 the list of power levels in dBm that will be the targets for the calibration. | |
106 | |
107 Crafting the txlevels calibration profiles for a new board design | |
108 ================================================================= | |
109 | |
110 If you are working with a new (or new-to-you) board design with no previous Tx | |
111 levels calibration experience, you need to begin by characterizing its Tx | |
112 output level behaviour so you can determine what APC values are appropriate for | |
113 the basis set, whether or not you need to shift the highest and/or lowest | |
114 target levels from their nominal spec values, and if some target shifting is | |
115 needed, which levels need to be shifted and by how much. | |
116 | |
117 The tool you will need for this investigation is fc-rfcal-txbasis. It requires | |
118 fc-cmu200d and rvinterf to be running, talking to the CMU200 and to the DUT, | |
119 respectively, and it takes the band number (850/900/1800/1900) and a set of | |
120 APC DAC values on the command line; no pre-existing txlevels profile is needed. | |
121 It commands the DUT to transmit at each of the specified APC DAC values in turn | |
122 and reports the power output levels measured by the CMU200. | |
123 | |
124 VERY IMPORTANT: You need to be very sure that your CMU200 or other measuring | |
125 instrument is itself in good calibration standing, i.e., that the measurements | |
126 it reports are trustworthy, and that the insertion loss in your cabling setup | |
127 (all the way from the actual DUT's antenna connector or RF test port to your | |
128 CMU200) really matches the numbers you have put in your cable configuration file | |
129 (see Cable-config-howto). If you fail to ensure these prerequisites, your | |
130 fc-rfcal-txbasis observations will be meaningless, as the cable insertion losses | |
131 are typically of the same order of magnitude as the transmitter differences you | |
132 are trying to determine. | |
133 | |
134 You will need to run fc-rfcal-txbasis with a guesstimated set of APC DAC values, | |
135 to be revised iteratively, and get a feel for what your DUT is putting out. | |
136 Are you able to hit the lowest spec power level consistently while the APC DAC | |
137 value remains well above zero? Are you able to hit the highest spec power level | |
138 as well, or does the measured power output fall short of this target no matter | |
139 how high you crank the APC DAC? These observations will tell you whether or not | |
140 you need to shift the highest and/or lowest target power levels in your new | |
141 txlevels calibration profile. | |
142 | |
143 Regular calibration runs | |
144 ======================== | |
145 | |
146 Once you have a good set of profiles for the type of Calypso GSM device you are | |
147 calibrating, just run fc-rfcal-txband with the band number and the name of your | |
148 profile. | |
149 | |
150 Checking existing calibration | |
151 ============================= | |
64 | 152 |
65 fc-rfcal-txcheck is a completely non-invasive program (does not make any writes | 153 fc-rfcal-txcheck is a completely non-invasive program (does not make any writes |
66 to any L1 RF tables or to FFS) that steps through all power levels for the | 154 to any L1 RF tables or to FFS) that steps through all power levels for the |
67 specified band (5-19 for EGSM or GSM850, or 0-15 for DCS or PCS), performs a | 155 specified band (5-19 for EGSM or GSM850, or 0-15 for DCS or PCS), performs a |
68 power measurement at each level, and displays the measured result. An | 156 power measurement at each level, and displays the measured result. |
69 equivalent operation will be the finishing sanity check step in the full Tx | |
70 power level calibration program. |