FreeCalypso > hg > freecalypso-tools

annotate target-utils/compalstage/README @ 416:30f6d1c32c6f

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doc/Flash-boot-defect article removed (no longer relevant) This article is no longer relevant because the issue in question only affected one (1) defective FCDEV3B board which was not and never will be sold.
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 26 Oct 2018 07:11:08 +0000
parents 56b1bab3e09b
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1 FreeCalypso loadtools have been designed from the beginning to work through
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2 the Calypso chip's own boot ROM. This approach works great for Openmoko and
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3 Pirelli targets, but Compal phones unfortunately have this Calypso boot ROM
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4 disabled at the board level. To run our own code in these phones instead of
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5 booting the regular firmware, we need to go through Compal's own boot code.
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6 The latter allows loading code into IRAM and jumping to it, but not in the
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7 same way as how we do it through the Calypso boot ROM.
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9 One could argue that the "proper" way to support these Compal phones would be
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10 to build a different version of our loadagent that is designed to be loaded
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11 through Compal's boot code instead of the Calypso boot ROM, and then redesign
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12 our fc-loadtool and fc-xram utilities to work with different loadagents loaded
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13 in different ways on different target devices. But I don't feel like doing
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14 that - too invasive to the once-clean design of loadtools.
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16 Hence I am adopting a different solution that works in the same way as
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17 OsmocomBB's "chain loading": the IRAM image that is fed to Compal's boot code
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18 is not our real loadagent, but a tiny piece of code that enables the Calypso
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19 boot ROM and jumps to it. All loadtools host programs will include this
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20 optional "Compal stage" at the beginning, enabled for targets that need it,
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21 but will then always fall into the Calypso boot ROM IRAM download path.
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23 The approach I'm adopting is doubly inefficient for Mot C139/140 phones whose
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24 bootloader effectively requires that the downloaded image be ~15 KiB long
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25 even when we only need to download 32 bytes. But hey, our ultimate goal is to
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26 produce our own Calypso phones, rather than hack those made by diabolical
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27 manufacturers who do not Respect Your Freedom; running our own firmware on the
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28 Mot C139 is only a transitional step, so making fc-loadtool/fc-xram entry
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29 slower by a second or two is probably an acceptable price for keeping the
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30 code clean for the boot-ROM-enabled free world.
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32 In this directory we build the several different versions of compalstage
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33 needed for different C1xx models.