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comparison target-utils/compalstage/README @ 314:48c08499cede

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compalstage binaries built
author Michael Spacefalcon <msokolov@ivan.Harhan.ORG>
date Wed, 02 Apr 2014 08:02:14 +0000
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313:9df7f9c72e17 314:48c08499cede
1 FreeCalypso loadtools have been designed from the beginning to work through
2 the Calypso chip's own boot ROM. This approach works great for Openmoko and
3 Pirelli targets, but Compal phones unfortunately have this Calypso boot ROM
4 disabled at the board level. To run our own code in these phones instead of
5 booting the regular firmware, we need to go through Compal's own boot code.
6 The latter allows loading code into IRAM and jumping to it, but not in the
7 same way as how we do it through the Calypso boot ROM.
8
9 One could argue that the "proper" way to support these Compal phones would be
10 to build a different version of our loadagent that is designed to be loaded
11 through Compal's boot code instead of the Calypso boot ROM, and then redesign
12 our fc-loadtool and fc-xram utilities to work with different loadagents loaded
13 in different ways on different target devices. But I don't feel like doing
14 that - too invasive to the once-clean design of loadtools.
15
16 Hence I am adopting a different solution that works in the same way as
17 OsmocomBB's "chain loading": the IRAM image that is fed to Compal's boot code
18 is not our real loadagent, but a tiny piece of code that enables the Calypso
19 boot ROM and jumps to it. All loadtools host programs will include this
20 optional "Compal stage" at the beginning, enabled for targets that need it,
21 but will then always fall into the Calypso boot ROM IRAM download path.
22
23 The approach I'm adopting is doubly inefficient for Mot C139/140 phones whose
24 bootloader effectively requires that the downloaded image be ~15 KiB long
25 even when we only need to download 32 bytes. But hey, our ultimate goal is to
26 produce our own Calypso phones, rather than hack those made by diabolical
27 manufacturers who do not Respect Your Freedom; running our own gsm-fw on the
28 Mot C139 is only a transitional step, so making fc-loadtool/fc-xram entry
29 slower by a second or two is probably an acceptable price for keeping the
30 code clean for the boot-ROM-enabled free world.
31
32 In this directory we build the several different versions of compalstage
33 needed for different C1xx models.