FreeCalypso > hg > freecalypso-tools
comparison target-utils/compalstage/README @ 0:e7502631a0f9
initial import from freecalypso-sw rev 1033:5ab737ac3ad7
| author | Mychaela Falconia <falcon@freecalypso.org> |
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| date | Sat, 11 Jun 2016 00:13:35 +0000 |
| parents | |
| children | 56b1bab3e09b |
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| 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. |