FreeCalypso > hg > fc-tourmaline

annotate doc/Voice-pseudo-modem @ 283:d9e3f3e293ac

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etm_audio.c: fix off-by-one error in auw of FIR coefficients The implementation of auw operation for UL or DL FIR upload had this bug: the number of 16-bit shortwords copied into the RVF-allocated temporary buffer was one too many, causing memory corruption errors. The present change fixes this bug.
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 08 Nov 2021 02:54:04 +0000
parents a62e5bf88434
children
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1 Back when TI's TCS211 fw existed in the traditional world of phone handset and
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2 cellular modem manufacturers, there were only two principal classes of target
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3 devices for it: handsets and modems. The former have local UI hardware (LCDs
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4 and keypads) and run firmware that works with this UI hw, the latter have no
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5 such hw and run firmware that expects to be controlled by an external host via
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6 AT commands.
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7
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8 But the peculiar circumstances under which our FreeCalypso family of projects
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9 operates give rise to a third possibility: what happens if one were to run
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10 non-UI-capable firmware that expects control via AT commands on a hardware
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11 target device that was originally designed to be an end user phone handset, in
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12 our case either Motorola C1xx or Pirelli DP-L10? The result is what I call a
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13 voice pseudo-modem (VPM): the phone's LCD stays dark, the buttons do nothing
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14 and the device expects to be controlled via AT commands as if it were a modem
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15 like the one in GTA01/02 smartphones, but there is no practically usable way to
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16 make use of any data services, only voice and SMS, hence my VPM term.
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17
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18 It needs to be noted clearly that the VPM hack described in this article is NOT
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19 a substitute for proper modem hardware - if your area of interest is Standard
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20 Modem functionality (the full set of GSM and GPRS services accessed via AT
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21 commands), then you need a proper hardware platform for it, either FCDEV3B or
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22 Caramel2. However, support for VPM operation in FreeCalypso exists for the
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23 following purposes:
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24
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25 * On some hw targets the VPM configuration can be an intermediate stepping stone
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26 toward potential future UI-enabled firmware - this situation holds on the
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27 C139.
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28
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29 * Being able to run FreeCalypso fw in the VPM configuration on Mot C1xx hw that
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30 many people already have and that may still be readily and cheaply available
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31 makes our firmware accessible to those who are not able to buy new FreeCalypso
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32 hardware.
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33
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34 * If you have a Pirelli DP-L10 phone (now very rare and hard to get, but were
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35 readily available in early 2013 when I started FreeCalypso): while there is
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36 unfortunately very little chance of being able to turn it into a practically
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37 usable Libre Dumbphone with FreeCalypso (the unwanted extra chips sans docs
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38 which we don't know how to power down are a killer), running FreeCalypso fw
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39 on the Pirelli in the VPM configuration is so easy and convenient that I do
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40 it all the time during development and testing.
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41
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42 Playing with FreeCalypso VPM on C1xx phones
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43 ===========================================
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44
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45 If a Mot C1xx phone is flashed with a FreeCalypso firmware image in the VPM
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46 configuration, it will behave as follows:
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47
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48 * The LCD will remain dark and the buttons will do nothing no matter what.
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49
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50 * If you plug in Motorola's charging adapter (it's a regulated 5 VDC power
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51 source, but with a non-USB connector) and you had properly installed the
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52 charging config file when creating the aftermarket FFS for FreeCalypso, the
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53 battery will charge. When you unplug the charging adapter, if there is no
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54 host computer running FC host program rvinterf connected to the phone
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55 serially, the phone will power off some 15 to 20 s after the charger unplug.
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56
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57 * If you press the power button while the phone is off, even momentarily, the
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58 phone will power on and boot (with nothing on the LCD as usual), but if the
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59 headset jack serial port is not connected to a computer running rvinterf, the
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60 firmware will execute a power-off after at most 20 s.
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61
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62 * In order to make the phone-turned-VPM do anything useful, you will need to
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63 connect the headset jack serial port to a host computer running FC host tools,
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64 run rvinterf to keep the phone alive (keep it from automatically powering
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65 off), and use FC host utility fc-shell to issue AT commands to it over the
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66 RVTMUX channel managed by rvinterf.
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67
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68 * The phone will remain on (i.e., the fw won't execute an automatic power-off)
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69 for as long as there is either a charging power adapter plugged in or a
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70 connected host computer running rvinterf - if there is no charging power,
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71 the fw will send periodic keepalive queries to check for the presence of a
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72 connected rvinterf process.
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73
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74 Playing with FreeCalypso VPM on a Pirelli DP-L10
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75 ================================================
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76
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77 There are two ways in which one can play with FC VPM firmware on a Pirelli:
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78
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79 * FC VPM fw can be flashed into the phone just like on Mot C1xx. To make this
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80 approach sensible, you will also need to craft and install a charging config
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81 file that will cause our FCHG driver to initiate the charging process
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82 automatically when the battery voltage falls below some sensible threshold,
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83 without requiring manual charging start via AT@CHG=1. In this case the
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84 reflashed phone will behave like C1xx in the previous section, except that
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85 the charging power source and the host computer connection are one and the
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86 same in the case of Pirelli's USB.
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87
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88 * The other approach is to keep Pirelli's original fw in the flash, let the
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89 phone function normally when not in the middle of a FreeCalypso VPM session,
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90 and load our FC VPM fw into RAM via fc-xram, making use of this phone's huge
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91 RAM that can hold an entire functional fw image without flashing. This is
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92 the Mother's preferred method.