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annotate doc/SIM-hardware-debugging @ 792:44e034f21916

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fc-simint: brown paper bag
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 19 Mar 2021 04:47:32 +0000
parents 0f138858ff39
children
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10e168596dfd doc/SIM-hardware-debugging: article written
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1 This article is only going to be of interest to those who are physically
10e168596dfd doc/SIM-hardware-debugging: article written
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2 producing Calypso-based hardware and therefore get to deal with the joys of
10e168596dfd doc/SIM-hardware-debugging: article written
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3 yield troubleshooting and failure analysis. If you are a mere user or software
10e168596dfd doc/SIM-hardware-debugging: article written
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4 developer working on known-good hardware made by someone other than you, then
10e168596dfd doc/SIM-hardware-debugging: article written
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5 none of the following applies to you.
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6
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7 Testing the SIM interface on a Calypso device
10e168596dfd doc/SIM-hardware-debugging: article written
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8 =============================================
10e168596dfd doc/SIM-hardware-debugging: article written
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9
10e168596dfd doc/SIM-hardware-debugging: article written
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10 A basic pass/fail test of the SIM interface is quite straightforward: simply
10e168596dfd doc/SIM-hardware-debugging: article written
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11 insert a test SIM into the socket (at FreeCalypso hw manufacturing we currently
10e168596dfd doc/SIM-hardware-debugging: article written
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12 use Sysmocom SIMs for this purpose) and issue an AT+CFUN=1 command to the
10e168596dfd doc/SIM-hardware-debugging: article written
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13 standard firmware; if the SIM interface hardware is good, the command will
10e168596dfd doc/SIM-hardware-debugging: article written
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14 complete successfully with an OK response, otherwise it will throw up an error.
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15
10e168596dfd doc/SIM-hardware-debugging: article written
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16 But what do you do when this basic test fails? If you get a "SIM not inserted"
10e168596dfd doc/SIM-hardware-debugging: article written
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17 error even though the SIM *is* in fact inserted, how do you debug it further?
10e168596dfd doc/SIM-hardware-debugging: article written
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18 In order to facilitate lower-level debugging of SIM interface woes, we have
10e168596dfd doc/SIM-hardware-debugging: article written
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19 implemented a standalone simtest program described in this article. To run
10e168596dfd doc/SIM-hardware-debugging: article written
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20 this simtest program on your Calypso device, run an fc-iram command like this:
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21
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22 fc-iram -h fcfam /dev/ttyXXX /opt/freecalypso/target-bin/simtest.srec
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23
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24 Like other interactive programs in our target-utils suite, this simtest program
10e168596dfd doc/SIM-hardware-debugging: article written
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25 will present a '=' prompt for you to type further commands. The following
10e168596dfd doc/SIM-hardware-debugging: article written
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26 sequence of commands should bring up the SIM interface if the hardware is good:
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27
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28 abbinit
10e168596dfd doc/SIM-hardware-debugging: article written
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29 volt 1.8
10e168596dfd doc/SIM-hardware-debugging: article written
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30 setup
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31 poll on
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32 reset 1
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33
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34 (Update for fc-host-tools-r11: the explicit abbinit command is no longer needed,
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35 but it is harmless to issue this extra command like before.)
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36
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37 You can change volt 1.8 to volt 3 if needed, but all recently made SIMs prefer
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38 1.8 V and merely tolerate higher voltages. TI's Iota ABB chip, which is what
10e168596dfd doc/SIM-hardware-debugging: article written
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39 we target in FreeCalypso, does not support 5V SIMs - it doesn't have a charge
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40 pump or any other boost converter to produce 5 V from lower battery voltages.
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41 (It is not just TI but all mobile chipset vendors; it has been a very long time
10e168596dfd doc/SIM-hardware-debugging: article written
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42 since anyone made a phone that can power 5V SIMs, and any old 5V-only SIMs have
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43 thus stopped being usable just as long ago.)
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44
10e168596dfd doc/SIM-hardware-debugging: article written
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45 If the hardware is good and you have a working SIM inserted in the socket as
10e168596dfd doc/SIM-hardware-debugging: article written
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46 you execute the above commands, you should see ATR bytes from your SIM appear
10e168596dfd doc/SIM-hardware-debugging: article written
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47 in your terminal window the moment you issue the last reset 1 command: that
10e168596dfd doc/SIM-hardware-debugging: article written
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48 final command transitions the SIM reset line from low to high, if the SIM has
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49 been given good power and clock prior to this event, this transition causes it
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50 to initialize and emit its Answer To Reset, and once you issue the poll on
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51 command, our simtest program listens for incoming bytes from the SIM at the
461
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52 same time while it listens for you to type further commands.
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53
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54 If you execute the above command sequence with a known-good SIM inserted in the
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55 socket and you don't see any ATR bytes on the final reset 1 command, then you
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56 have confirmed with a lower-level tool that your SIM interface hardware is
10e168596dfd doc/SIM-hardware-debugging: article written
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57 having some issues. Give it a poweroff command, rerun the fc-iram command to
10e168596dfd doc/SIM-hardware-debugging: article written
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58 get a fresh session, and get your oscilloscope ready. Now execute the commands
10e168596dfd doc/SIM-hardware-debugging: article written
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59 slowly, probing with your o'scope at each step:
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60
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61 abbinit
10e168596dfd doc/SIM-hardware-debugging: article written
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62 volt 1.8
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63
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64 The volt command enables the VRSIM regulator in the Iota ABB chip and causes it
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65 to put out the selected voltage. You should see this voltage appear on SIM
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66 socket contact C1 (VCC); if it fails to appear there, then trace out the circuit
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67 coming from VRSIM, and the VRSIM regulator itself (inside the chip) may also be
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68 suspect.
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69
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70 setup
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71
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72 This command puts the SIM interface block inside the Calypso into a sensible
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73 state and enables the SIM interface level shifters in the Iota ABB. After this
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74 command you should see a good 3.25 MHz clock (13 MHz divided by 4) with selected
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75 SIM voltage levels on the SIM CLK line (socket contact C3), the RST line (socket
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76 contact C2) should be low, and the I/O line (socket contact C7) should be high.
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77 The SIM clock is produced in the Calypso and then voltage-translated by a
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78 unidirectional buffer in the Iota ABB, thus if the clock fails to appear at the
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79 SIM socket, look for issues in that signal path. For the I/O line to be high
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80 at this point in the bring-up sequence, the resistor pull-ups on both DBB-to-ABB
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81 and ABB-to-socket sides need to be working; if the I/O line is high on the
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82 DBB-to-ABB side and the pull-up on the ABB-to-socket side is good, but the I/O
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83 line on the ABB-to-socket side is still low, then there may be something wrong
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84 with the level shifter in the ABB holding it low.
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85
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86 poll on
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87 reset 1
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88
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89 (The poll on command can be omitted if you are doing o'scope probing on an empty
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90 socket and thus not expecting any ATR.) As you issue that reset 1 command, hold
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91 your oscilloscope probe on SIM socket contact C2, which is the RST line - it
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92 should go from low to high. Our simtest utility's reset command (reset 0 or
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93 reset 1) manipulates one bit in one Calypso register that controls the Calypso
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94 chip's SIM_RST output, which then passes through a unidirectional level shifter
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95 in the Iota ABB on its way to SIM socket contact C2.
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96
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97 On those two FCDEV3B V2 boards that have been rejected as defective because of a
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98 non-working SIM interface and which are now being revisited for a more thorough
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99 investigation, we have not yet seen any problems with the SIM power supply
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100 voltage, with the SIM CLK line or with the I/O line pull-up, but on both boards
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101 the SIM RST line is not working: we see a constant low at socket contact C2
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102 (the only probe-able point in the entire SIM reset signal path), and reset 1
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103 produces no effect. Unfortunately there is no way to probe the DBBSRST signal
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104 going from Calypso to Iota (it goes from one BGA to the other on an inner layer
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105 without coming up to the surface except right under the two ball pads), thus it
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106 is too difficult to tell where the breakage occurs: is it the Calypso failing
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107 to put out a high on its SIM_RST output when commanded to do so by the register
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108 setting, is it some fault in the PCB shorting this signal to GND before it
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109 reaches Iota's DBBSRST input, is it some fault inside the Iota chip itself that
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110 causes it to put out a low on its SIMRST output even though the DBBSRST input
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111 is high, or is it some fault in the PCB shorting the ABB-to-socket SIM RST
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112 output to GND?
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113
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114 Given that FCDEV3B is not intended to be a high-volume product (we only need to
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115 make enough good boards to provide one to every interested developer or
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116 tinkerer), it will probably make more economic sense to simply reject SIM-
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117 defective boards and write them off as a loss than to spend astronomical amounts
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118 on PCB microsurgery to expose the DBBSRST signal for probing or other in-depth
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119 troubleshooting measures along those lines. For future board designs that may
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120 need to be produced in higher volumes, the Mother's current plan is to add
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121 probe-able test points on DBBSCK and DBBSRST lines, so that if similar problems
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122 recur, we'll be able to quickly isolate them to the Calypso side or the Iota
10e168596dfd doc/SIM-hardware-debugging: article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
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123 side.