FreeCalypso > hg > fc-rfcal-tools
changeset 35:5c0a6e536c70
doc/VCXO-notes renamed to VCXO-manual-cal
| author | Mychaela Falconia <falcon@freecalypso.org> |
|---|---|
| date | Tue, 23 May 2017 01:05:22 +0000 |
| parents | 99f753d4ccaf |
| children | d348d47f8a04 |
| files | doc/VCXO-manual-cal doc/VCXO-notes |
| diffstat | 2 files changed, 227 insertions(+), 227 deletions(-) [+] |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/doc/VCXO-manual-cal Tue May 23 01:05:22 2017 +0000 @@ -0,0 +1,227 @@ +How to calibrate the VCXO on your FreeCalypso development board +=============================================================== + +The process of calibrating the VCXO on a Calypso+Iota+Rita GSM MS consists of +the following fundamental parts: + +* The antenna needs to be disconnected and the FreeCalypso device's RF output + (SMA on the FCDEV3B) needs to be connected to an RF test station such as an + R&S CMU200. + +* The DUT is commanded to transmit semi-continuously as if it were transmitting + on TCH: Tx in one timeslot out of 8, but with the DUT running its own notion + of the TDMA frame not synchronized to anything, and keep transmitting + endlessly in 1/8 out of every 4.615 ms. + +* The RF test station connected to the DUT is used in the RF analyzer mode to + measure the frequency offset of the DUT's signal, relative to the ideal uplink + frequency corresponding to the selected ARFCN. + +* The above frequency offset measurement is performed with the AFC DAC on the + Calypso device set to different values, the results of the initial + measurements are used to guide some additional measurements, some computations + are made from these results, and the computed values are written into the + FreeCalypso device's FFS. + +This procedure is meant to be automated by way of a program that talks both to +the FreeCalypso DUT and to the RF test station and orchestrates all of the +measurement and computation steps, but until this program gets written (we +weren't able to get a hold of TI's original, hence we have to develop our own), +use the following instructions to perform the VCXO calibration procedure +manually. You still need a CMU200 or equivalent, though - it is not possible +to do any kind of calibration on a Calypso device by itself, without connecting +it to some appropriate RF test equipment. + +Reference documentation +======================= + +We have the following two TI documents which describe some of the RF calibration +procedures including the one for the VCXO: + +ftp://ftp.freecalypso.org/pub/GSM/Calypso/rf_calibration.pdf + +https://www.freecalypso.org/LoCosto-docs/Production%20test%20and%20calibration/i_sample_rf_test_and_calibration_13_03_04_01991%20-%20v026.pdf + +Unfortunately neither of them corresponds to the exact evolutionary time point +of interest to us: the first one corresponds to some chipset much earlier than +the one we are working with, and to firmware versions much earlier than ours, +whereas the second one is for TI's later LoCosto chipset. + +Commanding the DUT to transmit semi-continuously +================================================ + +There is only one VCXO calibration that is subsequently used for all bands in +normal MS operation. Both of the calibration instruction documents above +instruct the operator to run the Tx in GSM900 mode on ARFCN 40, hence we shall +do likewise until and unless we find some good reason to do differently. + +Issue the following commands through fc-tmsh to start the semi-continuous Tx: + +tms 1 # enter RF Test Mode +rfpw 7 6 0 # select GSM 900+1800 band pair, GSM900 band within the pair +rfpw 2 40 # set ARFCN to 40 +rfpw 8 0 # disable AFC algorithm, i.e., control the AFC DAC manually +txpw 1 12 # Tx power level +rfe 3 # start Rx & Tx without network sync + +WARNING: Before issuing the above commands, ensure that the antenna is +disconnected and that the RF output will be going into your test equipment, +not on the air! Do not EVER issue these commands with a real antenna connected, +unless your intent is to operate a rogue transmitter or jammer. + +At this point your CMU200 or equivalent should detect the uplink signal +generated by the DUT (on the CMU200 one needs to set TSC to 5, dunno about +other test equipment), and you should see some frequency offset. + +The actual calibration procedure +================================ + +1. Set the AFC DAC to -2048: + + rfpw 9 -2048 + + and measure the frequency offset. Note it down. + +2. Set the AFC DAC to +2048: + + rfpw 9 2048 + + and again measure the frequency offset. Note it down. + +Now you need to create an ASCII text file with your frequency offset +measurements. Each line represents one measurement and consists of two fields: +the first field is the DAC value and the second field is the measured frequency +offset in Hz. On my FCDEV3B S/N 001 the first two measurements were: + +-2048 -30008 ++2048 +21394 + +Next you need to apply a linear model to the VCXO frequency offset as a function +of the DAC input: if x is the DAC value and F is the resulting frequency offset, +then the linear model is F = ax + b, where a and b need to be determined from +two measured points (x1, F1) and (x2, F2). Then once you have a and b, find the +x value that should produce F = 0. The fc-vcxo-linear utility will do this math +for you: run it with the name of your text file with measurements as its only +argument. + +With my measurements, the DAC_CENTER value computed by fc-vcxo-linear is 343. +However, the linear model is not perfect, thus when you write this computed +value into the DAC with the rfpw 9 command, the resulting frequency offset on +the CMU200 screen may be quite far from 0. + +TI's instructions in the LoCosto document direct the calibration operator to do +two more measurements at DAC_CENTER-100 and DAC_CENTER+100, where DAC_CENTER is +the value we just computed by applying the linear model to the first two +measurements. However, in my case the frequency offset at DAC=343 (DAC_CENTER) +was so negative that at DAC=443 (DAC_CENTER+100) it was still negative - and I +assume that TI's intent was to capture a close range around the zero crossing. + +Therefore, when I get to writing the automated calibration program, I intend to +change this part of the algorithm as follows: instead of adding or subtracting +100 right now, first do an rfpw 9 with the DAC_CENTER value as computed from +the linear model, make a frequency offset measurement, and see if it is negative +or positive. Then step the DAC value in the appropriate direction by some +reasonable increment (e.g., 100) until the frequency offset changes sign. Then +take the two DAC values closest to the output frequency offset sign change. + +After doing the above, my measurement notes file became: + +-2048 -30008 ++2048 +21394 +443 -669 +543 634 + +This file needs to contain all four measurements, with the first two being at +the extreme DAC values and with the second two hugging the empirically located +zero crossing, when you feed it to the next step: + +fc-vcxo-param myvcxo.meas + +The fc-vcxo-param utility will compute the final math steps to produce the +actual calibration values which will need to be uploaded to the FreeCalypso +device and stored in its FFS. With my measurements above, I got the following +output: + +rf_table afcparams + + 3434 # Psi_sta_inv + 15 # Psi_st + 1000341 # Psi_st_32 + 4293 # Psi_st_inv + + 3954 # DAC_INIT * 8 + -5860 # DAC_MIN * 8 + 11351 # DAC_MAX * 8 + 2560 # snr_thr + +# DAC_INIT: rfpw 10 494 + +The output from fc-vcxo-param is in the rf_table format which our implementation +of the rftw command takes as input, and the latter is the fc-tmsh command which +you will need to issue in order to send this table to the FreeCalypso firmware +in the DUT. + +Explanation of the numbers: + +* The Psi constants are computed from the slope of the VCXO, and are + subsequently used for the steering: when the DSP reports a particular + frequency offset (in the form of an angle in radians), by how much should the + DAC value be adjusted? The slope I use for computing these Psi constants is + the one from the first two measurements at the extreme DAC values, as the + LoCosto document seems to indicate. + +* DAC_INIT is the DAC value at which the resulting frequency offset should be 0; + it is computed per the linear model from the second pair of measurements. + +* DAC_MIN and DAC_MAX are the DAC values which should produce frequency offsets + of -15 and +15 ppm, respectively, according to the LoCosto document. I + compute them per the linear model from the first pair of measurements (the + extreme DAC ones), as that is what the LoCosto document says. + +* The SNR threshold is a constant that never needs to change. + +The 3 dac_* values in the afcparams structure are stored in the times 8 form. +Examination of the afcparams values read out of several Openmoko-made GTA02 +units shows that the low 3 bits aren't necessarily zeros, indicating that TI's +calibration program probably multiplied by 8 before converting from floating +point to integer; I do likewise in fc-vcxo-param. + +Examination of the same afcparams values read out of Openmoko-made units also +shows that the center, min and max DAC values do vary quite a bit from one unit +to the next, whereas the Psi constants change very little. The Psi constants +which my program computed from my manual measurements on FCDEV3B S/N 001 are in +the same range as those read out of Openmoko-made units, which is definitely a +reassuring sign. + +Writing your VCXO calibration into FFS +====================================== + +Save the fc-vcxo-param output in a file, e.g.: + +fc-vcxo-param myvcxo.meas myvcxo.param + +Upload the generated afcparams table to your FreeCalypso device: + +rftw 9 myvcxo.param + +There is one more variable in the firmware, outside of the afcparams structure, +which also holds the DAC_INIT value. Set it with an rfpw 10 command as +instructed in the last comment line emitted by fc-vcxo-param; in my case it was: + +rfpw 10 494 + +Now save all of these values in the non-volatile flash file system: + +me 102 +me 103 + +Cleaning up +=========== + +To shut off the transmitter you started earlier, issue this command: + +rfe 0 + +Now power off your FreeCalypso device, disconnect the RF test setup, connect the +antenna back, insert a SIM, do a fresh boot and see if you can connect to a real +live GSM network with your VCXO calibration!
--- a/doc/VCXO-notes Tue May 23 00:33:10 2017 +0000 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,227 +0,0 @@ -How to calibrate the VCXO on your FreeCalypso development board -=============================================================== - -The process of calibrating the VCXO on a Calypso+Iota+Rita GSM MS consists of -the following fundamental parts: - -* The antenna needs to be disconnected and the FreeCalypso device's RF output - (SMA on the FCDEV3B) needs to be connected to an RF test station such as an - R&S CMU200. - -* The DUT is commanded to transmit semi-continuously as if it were transmitting - on TCH: Tx in one timeslot out of 8, but with the DUT running its own notion - of the TDMA frame not synchronized to anything, and keep transmitting - endlessly in 1/8 out of every 4.615 ms. - -* The RF test station connected to the DUT is used in the RF analyzer mode to - measure the frequency offset of the DUT's signal, relative to the ideal uplink - frequency corresponding to the selected ARFCN. - -* The above frequency offset measurement is performed with the AFC DAC on the - Calypso device set to different values, the results of the initial - measurements are used to guide some additional measurements, some computations - are made from these results, and the computed values are written into the - FreeCalypso device's FFS. - -This procedure is meant to be automated by way of a program that talks both to -the FreeCalypso DUT and to the RF test station and orchestrates all of the -measurement and computation steps, but until this program gets written (we -weren't able to get a hold of TI's original, hence we have to develop our own), -use the following instructions to perform the VCXO calibration procedure -manually. You still need a CMU200 or equivalent, though - it is not possible -to do any kind of calibration on a Calypso device by itself, without connecting -it to some appropriate RF test equipment. - -Reference documentation -======================= - -We have the following two TI documents which describe some of the RF calibration -procedures including the one for the VCXO: - -ftp://ftp.freecalypso.org/pub/GSM/Calypso/rf_calibration.pdf - -https://www.freecalypso.org/LoCosto-docs/Production%20test%20and%20calibration/i_sample_rf_test_and_calibration_13_03_04_01991%20-%20v026.pdf - -Unfortunately neither of them corresponds to the exact evolutionary time point -of interest to us: the first one corresponds to some chipset much earlier than -the one we are working with, and to firmware versions much earlier than ours, -whereas the second one is for TI's later LoCosto chipset. - -Commanding the DUT to transmit semi-continuously -================================================ - -There is only one VCXO calibration that is subsequently used for all bands in -normal MS operation. Both of the calibration instruction documents above -instruct the operator to run the Tx in GSM900 mode on ARFCN 40, hence we shall -do likewise until and unless we find some good reason to do differently. - -Issue the following commands through fc-tmsh to start the semi-continuous Tx: - -tms 1 # enter RF Test Mode -rfpw 7 6 0 # select GSM 900+1800 band pair, GSM900 band within the pair -rfpw 2 40 # set ARFCN to 40 -rfpw 8 0 # disable AFC algorithm, i.e., control the AFC DAC manually -txpw 1 12 # Tx power level -rfe 3 # start Rx & Tx without network sync - -WARNING: Before issuing the above commands, ensure that the antenna is -disconnected and that the RF output will be going into your test equipment, -not on the air! Do not EVER issue these commands with a real antenna connected, -unless your intent is to operate a rogue transmitter or jammer. - -At this point your CMU200 or equivalent should detect the uplink signal -generated by the DUT (on the CMU200 one needs to set TSC to 5, dunno about -other test equipment), and you should see some frequency offset. - -The actual calibration procedure -================================ - -1. Set the AFC DAC to -2048: - - rfpw 9 -2048 - - and measure the frequency offset. Note it down. - -2. Set the AFC DAC to +2048: - - rfpw 9 2048 - - and again measure the frequency offset. Note it down. - -Now you need to create an ASCII text file with your frequency offset -measurements. Each line represents one measurement and consists of two fields: -the first field is the DAC value and the second field is the measured frequency -offset in Hz. On my FCDEV3B S/N 001 the first two measurements were: - --2048 -30008 -+2048 +21394 - -Next you need to apply a linear model to the VCXO frequency offset as a function -of the DAC input: if x is the DAC value and F is the resulting frequency offset, -then the linear model is F = ax + b, where a and b need to be determined from -two measured points (x1, F1) and (x2, F2). Then once you have a and b, find the -x value that should produce F = 0. The fc-vcxo-linear utility will do this math -for you: run it with the name of your text file with measurements as its only -argument. - -With my measurements, the DAC_CENTER value computed by fc-vcxo-linear is 343. -However, the linear model is not perfect, thus when you write this computed -value into the DAC with the rfpw 9 command, the resulting frequency offset on -the CMU200 screen may be quite far from 0. - -TI's instructions in the LoCosto document direct the calibration operator to do -two more measurements at DAC_CENTER-100 and DAC_CENTER+100, where DAC_CENTER is -the value we just computed by applying the linear model to the first two -measurements. However, in my case the frequency offset at DAC=343 (DAC_CENTER) -was so negative that at DAC=443 (DAC_CENTER+100) it was still negative - and I -assume that TI's intent was to capture a close range around the zero crossing. - -Therefore, when I get to writing the automated calibration program, I intend to -change this part of the algorithm as follows: instead of adding or subtracting -100 right now, first do an rfpw 9 with the DAC_CENTER value as computed from -the linear model, make a frequency offset measurement, and see if it is negative -or positive. Then step the DAC value in the appropriate direction by some -reasonable increment (e.g., 100) until the frequency offset changes sign. Then -take the two DAC values closest to the output frequency offset sign change. - -After doing the above, my measurement notes file became: - --2048 -30008 -+2048 +21394 -443 -669 -543 634 - -This file needs to contain all four measurements, with the first two being at -the extreme DAC values and with the second two hugging the empirically located -zero crossing, when you feed it to the next step: - -fc-vcxo-param myvcxo.meas - -The fc-vcxo-param utility will compute the final math steps to produce the -actual calibration values which will need to be uploaded to the FreeCalypso -device and stored in its FFS. With my measurements above, I got the following -output: - -rf_table afcparams - - 3434 # Psi_sta_inv - 15 # Psi_st - 1000341 # Psi_st_32 - 4293 # Psi_st_inv - - 3954 # DAC_INIT * 8 - -5860 # DAC_MIN * 8 - 11351 # DAC_MAX * 8 - 2560 # snr_thr - -# DAC_INIT: rfpw 10 494 - -The output from fc-vcxo-param is in the rf_table format which our implementation -of the rftw command takes as input, and the latter is the fc-tmsh command which -you will need to issue in order to send this table to the FreeCalypso firmware -in the DUT. - -Explanation of the numbers: - -* The Psi constants are computed from the slope of the VCXO, and are - subsequently used for the steering: when the DSP reports a particular - frequency offset (in the form of an angle in radians), by how much should the - DAC value be adjusted? The slope I use for computing these Psi constants is - the one from the first two measurements at the extreme DAC values, as the - LoCosto document seems to indicate. - -* DAC_INIT is the DAC value at which the resulting frequency offset should be 0; - it is computed per the linear model from the second pair of measurements. - -* DAC_MIN and DAC_MAX are the DAC values which should produce frequency offsets - of -15 and +15 ppm, respectively, according to the LoCosto document. I - compute them per the linear model from the first pair of measurements (the - extreme DAC ones), as that is what the LoCosto document says. - -* The SNR threshold is a constant that never needs to change. - -The 3 dac_* values in the afcparams structure are stored in the times 8 form. -Examination of the afcparams values read out of several Openmoko-made GTA02 -units shows that the low 3 bits aren't necessarily zeros, indicating that TI's -calibration program probably multiplied by 8 before converting from floating -point to integer; I do likewise in fc-vcxo-param. - -Examination of the same afcparams values read out of Openmoko-made units also -shows that the center, min and max DAC values do vary quite a bit from one unit -to the next, whereas the Psi constants change very little. The Psi constants -which my program computed from my manual measurements on FCDEV3B S/N 001 are in -the same range as those read out of Openmoko-made units, which is definitely a -reassuring sign. - -Writing your VCXO calibration into FFS -====================================== - -Save the fc-vcxo-param output in a file, e.g.: - -fc-vcxo-param myvcxo.meas myvcxo.param - -Upload the generated afcparams table to your FreeCalypso device: - -rftw 9 myvcxo.param - -There is one more variable in the firmware, outside of the afcparams structure, -which also holds the DAC_INIT value. Set it with an rfpw 10 command as -instructed in the last comment line emitted by fc-vcxo-param; in my case it was: - -rfpw 10 494 - -Now save all of these values in the non-volatile flash file system: - -me 102 -me 103 - -Cleaning up -=========== - -To shut off the transmitter you started earlier, issue this command: - -rfe 0 - -Now power off your FreeCalypso device, disconnect the RF test setup, connect the -antenna back, insert a SIM, do a fresh boot and see if you can connect to a real -live GSM network with your VCXO calibration!