FreeCalypso > hg > freecalypso-tools
annotate doc/Binary-file-formats @ 699:c354c261f635
CHANGES: fc-iram fix documented
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Tue, 31 Mar 2020 03:37:24 +0000 |
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doc: new articles Binary-file-formats and Flash-programming
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1 In FreeCalypso we use 3 different file formats for Calypso binary images, i.e., |
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2 code images to be loaded into either flash or RAM or retrieved flash dumps. |
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3 These 3 different file formats are straight binary (*.bin), moko-style m0 (*.m0) |
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4 and little-endian S-records (*.srec). |
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5 |
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6 Straight binary (*.bin) |
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7 ======================= |
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8 |
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9 Straight binary is our preferred format for flash dumps. It is written in the |
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10 native little-endian byte order of the Calypso ARM7 processor, i.e., the order |
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11 of bytes in the raw binary file directly corresponds to incrementing byte |
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12 addresses as visible to the ARM7 - any ASCII strings in the image thus appear |
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13 naturally. We also use the same straight binary format in native LE byte order |
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14 for flashable code images generated with the gcc+binutils toolchain (as opposed |
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15 to TI's TMS470), generated with arm-elf-objcopy -O binary - although we don't |
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16 have too many such code images currently given that neither FC Citrine nor FC |
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17 Selenite ever achieved production quality. |
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18 |
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19 Another unrelated use of this straight binary format is for RAM-loadable code |
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20 images that are fed to Compal's bootloader (Motorola C1xx and Sony Ericsson |
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21 J100) as opposed to Calypso boot ROM. Our generally preferred image format for |
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22 RAM-loadable code pieces is little-endian S-records (*.srec, see below), but |
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23 for Compal's bootloader we use straight binary instead because of the way this |
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24 bootloader protocol works. |
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25 |
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26 moko-style m0 |
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27 ============= |
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28 |
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29 This format is a variant of Motorola hex (S-records), a variant invented by TI |
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30 rather than by us. This format is produced by TI's hex470 tool when run with |
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31 -m -memwidth 16 -romwidth 16 options, which is the configuration used by TI in |
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32 the Calypso program, and is read by TI's flash programming tool called FLUID. |
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33 TI used this format not only for flashable firmware images, but also for various |
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34 RAM-loadable code pieces, particularly those that comprise the target-side |
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35 component of FLUID. |
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36 |
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37 The special quirk of this S-record variant format is its peculiar byte order. |
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38 TI viewed it as "16-bit hex", meaning that the image is logically viewed as |
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39 consisting of 16-bit words rather than 8-bit bytes, each S3 record carries an |
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40 even number of bytes to be loaded at an even address, and each 16-bit word |
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41 (4 hex digits) appears in these S3 records with its most-significant hex nibble |
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42 toward the left, just like the address field of each S-record. But if this |
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43 image gets interpreted by some more naive tool (for example, objcopy from GNU |
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44 binutils) as bytes rather than 16-bit words, the result will be a reversed byte |
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45 order, with all strings etc messed up. |
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46 |
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47 In FreeCalypso we use this moko-style m0 format (our new name for what TI called |
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48 16-bit hex) only for flashable firmware images built with TI's TMS470 toolchain |
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49 (can be our own FC Magnetite or historical ones built by Openmoko or other |
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50 similar historical vendors), but never for any RAM-loadable code pieces - we use |
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51 little-endian SREC for the latter as explained below. |
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52 |
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53 And what about the name? Why do we call it moko-style m0 rather than just m0? |
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54 The reason is because Compal muddied our waters by introducing their own *.m0 |
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55 files that were generated with -memwidth 8 -romwidth 8 instead of -memwidth 16 |
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56 -romwidth 16, producing 8-bit hex instead of 16-bit hex. We do not support |
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57 Compal's different *.m0 files at all, and we needed some name to specifically |
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58 identify TI-style m0 files rather than Compal-style. We ended up with the name |
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59 moko-style rather than TI-style because we already had our mokosrec2bin program |
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60 going back to 2013-04-15, one of the very first programs written in the |
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61 FreeCalypso family of projects: our very first encounter with this file format |
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62 were mokoN firmware images put out in this *.m0 format by That Company. |
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63 |
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64 Little-endian S-records (*.srec) |
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65 ================================ |
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66 |
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67 Back at the beginning of FreeCalypso in the spring/summer of 2013 I (Mother |
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68 Mychaela) decided to use S-records instead of straight binary for our |
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69 RAM-loadable code pieces, i.e., code that is loaded into RAM either through the |
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70 Calypso boot ROM (fc-iram) or by chain-loading via loadagent (fc-xram). I made |
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71 this decision based on two factors: |
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72 |
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73 1) ARM code generated by common toolchains (both TI's TMS470 and gcc+binutils) |
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74 without special contortions is not position-independent: a code image that |
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75 was linked for a given address needs to be loaded at that specific address, |
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76 not some other. |
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77 |
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78 2) An S-record image has its load address embedded in the image itself, whereas |
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79 a raw binary naturally does not carry any such extra metadata. |
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80 |
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81 With SREC as the standardized hand-off format from code generation tools to |
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82 loadtools, the choice of load address is made entirely on the code generation |
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83 side; loadtools do not impose a fixed load address, nor do they require it to |
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84 be communicated via extra command line arguments or options. |
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85 |
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86 However, the variant of SREC we use for RAM-loadable code pieces is not the same |
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87 as moko-style m0 - the byte order is the opposite, with our RAM-loadable code |
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88 pieces using the native little-endian byte order of the ARM7 processor as the |
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89 byte order within S3 records. Prior to the introduction of RAM-loadable FC |
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90 Magnetite fw images for Pirelli DP-L10 in late 2016 (and then likewise for our |
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91 own FCDEV3B), the only RAM-loadable code pieces we have had were built with |
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92 gcc+binutils, not with TMS470, and GNU binutils got a different take on the |
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93 S-record format than TI did: they generate byte-oriented SREC files, with the |
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94 byte order being the same as it would be in a straight binary file, matching |
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95 the target processor's memory byte addressing order. Thus GNU-style SREC has |
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96 been adopted as the format for our RAM-loadable code images for both fc-iram |
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97 and fc-xram, as opposed to TI-style SREC aka moko-style m0. The convention we |
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98 have adopted is that *.m0 filename suffix means TI-style aka moko-style, |
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99 whereas *.srec means GNU-style. |
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100 |
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101 Besides the S3 record byte order, there is one other difference between TI-built |
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102 *.m0 code images and GNU-built *.srec ones: the final S7 record carries the |
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103 entry point address in GNU-built *.srec images, whereas TI's *.m0 images always |
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104 have a zero dummy address in there. Our fc-iram and fc-xram tools require the |
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105 real entry point address in the S7 record. |
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106 |
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107 How do we generate ramimage.srec RAM-loadable images for fc-xram in FC |
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108 Magnetite? Answer: FC Magnetite build system includes a special ad hoc |
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109 converter program that reads ramimage.m0 produced by TI's hex470 tool and |
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110 produces ramimage.srec: it reverses the order of bytes, adds another S3 record |
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111 that writes the boot-ROM-redirected interrupt and exception vectors and |
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112 generates an S7 record with the right entry point address. |
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113 |
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114 This little-endian *.srec format is actively used only for RAM-loadable code |
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115 pieces in FreeCalypso, not for anything that goes into or gets read from flash. |
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116 We do have flash dump2srec and flash program-srec commands in fc-loadtool, they |
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117 were implemented back in the founding stage of FreeCalypso in 2013 for the sake |
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118 of completeness and symmetry (it seemed right to support both binary and |
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119 S-record formats), but they never got any practical use: if you are making a |
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120 flash dump, you would normally want to examine it afterward, and any such |
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121 examination almost always needs a straight binary image, not S-records. |