FreeCalypso > hg > freecalypso-sw
annotate doc/Roadmap @ 664:d36f647c2432
gsm-fw/comlib: initial import of TI's source
cl_des.c and cl_imei.c are from the Leonardo semi-src; others are from LoCosto
author | Michael Spacefalcon <msokolov@ivan.Harhan.ORG> |
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date | Sun, 28 Sep 2014 05:09:53 +0000 |
parents | 6500e1817d9b |
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1 The ultimate goal of the FreeCalypso project is to produce a GSM firmware |
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2 version that: |
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3 |
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4 a) runs on the Calypso targets of interest to us: not only the FIC/Openmoko |
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5 GTA0x GSM modem, but also some complete dumbphones like Mot C139 and/or |
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6 Pirelli DP-L10; |
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7 |
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8 b) operates each target device it runs on in a way that is practically usable: |
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9 to me (lead developer Space Falcon) practical usability means providing a |
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10 standard AT command interface on modems like GTA0x and operating as a self- |
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11 contained standard cellphone with a UI on complete "dumbphone" targets; |
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12 |
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13 c) is rebuildable from source in a way that would allow us to exercise the |
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14 traditional Four Freedoms of free software as defined by the FSF. |
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15 |
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16 Our starting point is TI's Leonardo reference firmware version from Sotovik, a |
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17 mixture of source and linkable binary object modules. It can be built into a |
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18 complete and functional firmware image with TI's TMS470 compiler+linker+etc |
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19 toolchain, and can run on two hardware targets: |
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20 |
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21 a) TI's Leonardo development board for the Calypso/Iota/Rita chipset - |
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22 legendary unobtainium hardware; |
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23 |
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24 b) FIC/Openmoko GTA0x GSM modem - while this device is *not* what I wish to use |
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25 with the "end user" hat on, it is an available and working hw platform for |
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26 development. |
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27 |
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28 This Leonardo starting point does kinda-sorta satisfy the "rebuildable from |
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29 source" requirement, as I was able to port it from the Leonardo board to the |
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30 GTA0x modem, but it is still quite far from what the FreeCalypso project |
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31 ultimately seeks to achieve. |
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32 |
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33 What I, the lead developer, ultimately seek is not an AT-controlled modem |
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34 embedded in a "Linux" smartphone, but a complete and standalone "dumbphone", |
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35 with the UI driven by the Calypso. Transforming our starting and working |
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36 reference version from something that runs on the GTA0x modem and presents an |
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37 AT command interface into something that can run on a complete "dumbphone" and |
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38 present a self-contained UI can be done in several possible ways: |
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39 |
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40 1. One could proceed further with the same approach that was used to produce |
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41 leo2moko: keep making small incremental changes to the Leonardo semi-src, |
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42 while keeping most of the binary object blobs intact at least initially, and |
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43 sticking with the original proprietary TMS470 compiler toolchain (running |
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44 under wine, as it's a bunch of M$ Windows binaries) throughout the journey. |
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45 |
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46 Advantage: no massive "forklift" step required at the very beginning of the |
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47 journey, one can do small incremental steps instead. One possible roadmap |
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48 with this approach might be (just thinking out loud here) to start with |
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49 finding a way to redirect the AT command channel to something wrapped inside |
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50 RVTMUX, then port the fw to run on a target like Pirelli DP-L10, still |
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51 controlled via AT commands but passed via RVTMUX, and then try to add the |
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52 "dumbphone" UI layers. Some of the binary object blobs would certainly need |
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53 to be "cracked" and modified in this process, most sensibly by replacing |
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54 each blob in need of modification with a reconstructed source piece, but |
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55 this work would be done incrementally, rather than in a massive "forklift" |
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56 step upfront. |
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57 |
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58 Disadvantage: this approach requires sticking with the original proprietary |
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59 compiler toolchain throughout at least most of the journey, which means |
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60 keeping the Weendoze poison that toolchain comes with. This aspect was |
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61 enough to turn me personally away from this approach. |
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62 |
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63 2. One could move away from the proprietary compiler toolchain and replace it |
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64 with gcc, while still retaining those parts of the Leonardo firmware for |
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65 which we only have linkable binary objects but no C source, by teaching the |
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66 GNU toolchain (gcc+binutils) to emulate the TMS470 compiler's ABI: COFF |
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67 objects, a very different way of doing ARM/Thumb interworking, and a host of |
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68 other differences from how the GNU toolchain for ARM normally does things. |
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69 (I've done similar work on GCC and GNU Binutils in the past; let us not |
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70 forget that GNU started out by emulating various inter-component interfaces, |
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71 including ABIs, of various proprietary Unix versions.) |
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72 |
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73 The advantage of this approach should be obvious. While in the long run we |
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74 would certainly like to get rid of all binary object blobs and replace them |
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75 with reconstructed source pieces, life would be much easier if we could do |
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76 this work incrementally, one blob at a time in a regression-tested working |
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77 fw version, rather than all upfront. |
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78 |
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79 Disadvantage: teaching gcc and binutils to emulate TI's TMS470 ABI well |
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80 enough to where one could compile some sources with gcc, link the resulting |
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81 .o's with TI's blobs and get a working fw image at the end would be no easy |
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82 matter. In fact, it would be a massive amount of work, and considering that |
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83 this work would serve absolutely no purpose but to allow linking with some |
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84 proprietary binary blobs, finding the justification for the effort would be |
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85 difficult. |
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86 |
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87 3. The approach I am currently following is the most ambitious one: start by |
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88 deblobbing the firmware, i.e., replacing all binary object blobs with |
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89 reconstructed source pieces, and then simply compile the all-C source with |
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90 the GNU toolchain for ARM7 in its default ABI. |
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91 |
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92 Advantage: having the firmware in the form of full C source that builds with |
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93 a free compiler (a compiler that is itself bona fide Free Software) is |
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94 obviously the ultimate best. No blobs means no need to waste creative energy |
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95 on emulating proprietary compiler ABIs. |
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96 |
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97 Disadvantage: all the hardest work is upfront, and needs to be done in a |
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98 "forklift" manner. |
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99 |
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100 It should be obvious that incrementality, or division into manageable, bite- |
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101 sized pieces, is an essential requirement for successful execution of any large |
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102 scale project, and FreeCalypso is no different. Because our chosen approach |
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103 unfortunately does not allow us to make small incremental modifications to a |
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104 fully functional fw version, I currently achieve the needed incrementality in a |
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105 different way: by starting out with a firmware "skeleton" that compiles into an |
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106 image and runs on the hardware, but does nothing useful yet, and then slowly |
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107 adding chunks of "meat" to this skeleton in incremental steps aiming in the |
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108 direction of the complete & working fw version that is our reference. As I add |
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109 each "chunk of meat" to our gcc-built gsm-fw, I test it on the hardware and |
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110 compare its operation against the leo2moko reference version - that is our form |
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111 of pseudo-regression testing. |
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112 |
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113 Where the missing source bits come from |
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114 ======================================= |
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115 |
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116 How can we replace a binary object blob with a corresponding source piece if we |
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117 lack the original source? In two ways: |
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118 |
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119 1. In many cases we can lift the corresponding source piece from another TI |
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120 source leak, e.g., the LoCosto one. Calypso and LoCosto chipsets are |
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121 different, so code specific to LoCosto hardware won't run on Calypso targets, |
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122 but much of the code is chipset-independent. The LoCosto source leak is |
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123 important because it contains real C source for many of the chipset- |
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124 independent components for which our Leonardo reference version has only |
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125 binary blobs. |
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126 |
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127 2. When no original or suitable substitute source can be found anywhere, we |
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128 have to bite the bullet, pass the blob through a suitable disassembler (I |
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129 wrote one that is specifically taylored for reversing code built with the |
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130 TMS470 compiler), and then write a piece of new C code that replicates the |
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131 logic found in the disassembled blob. |