Introduction
Many people bought many different phones, and some of them whish to help replicant and/or to port replicant to their phones or devices.
This guide will show what was done for the htc dream, so these people can understand the process better.
When talking about porting, this page talks about re-using existing product definitions. You will not learn how to
build Android for a device not currently supported by Android. Instead, you will learn how to build a version of
[Cyanogenmod http://www.cyanogenmod.com/] without proprietary parts.
To gain more insight in the Android build system, refer to [http://source.android.com/porting/build_system.html Android Build System documentation] which is part of
[http://source.android.com/porting/ Android Platform Developer's Guide]. You should find an answer there if you have any questions about the Makefiles referenced in this document. Terminology
The RIL is the radio interface library, that is to say, a library that talks to the modem, usually (but not always) trough AT commands.
Basically the modem runs on a separate CPU,and there is some sort of communication needed between the main CPU and the modem CPU to make telephony work. For instance, the modem must tell you when you've got a call, and you must tell the modem that you want to call someone.
TODO: point to 0707 standard or newer Help with source code
Keep in mind that on most devices, the full source code of the kernel is released.
However, some userspace libraries, or dlopened libraries (libraries loaded at runtime after the application started) are proprietary software,
so if you're porting to a new CPU/SOC keep in mind that you have the source code to the kernel interfaces.
That can help a lot, and sometimes there is even some sort of documentation in the headers. Build the source

The first thing to do is to download the replicant sources:
[wiki:BuildDream] can be used as a reference: download and build the sources for your device.
Let's say the user has a HTC Wildfire. It is useful to know the codename of the device in question, which is "Buzz" in case
of the Wildfire.

You need to configure the build tree for our device. By default, a generic image
for the Android emulator will be built.
In [wiki:BuildDream], you would use the following command to set up the build: {{{
lunch cyanogen_dream_sapphire-eng
}}}
Now, since you are not building for the HTC dream, you need to identify the right command that corresponds to your device.
In order to do that, run the following command and look at its output. {{{
$ source build/envsetup.sh
including device/geeksphone/one/vendorsetup.sh
including device/htc/ace/vendorsetup.sh
including device/htc/bravoc/vendorsetup.sh
including device/htc/bravo/vendorsetup.sh
including device/htc/buzz/vendorsetup.sh
including device/htc/glacier/vendorsetup.sh
including device/htc/heroc/vendorsetup.sh
including device/htc/inc/vendorsetup.sh
including device/htc/legend/vendorsetup.sh
including device/htc/liberty/vendorsetup.sh
including device/htc/supersonic/vendorsetup.sh
including device/htc/vision/vendorsetup.sh
including device/motorola/sholes/vendorsetup.sh
including device/nvidia/harmony/vendorsetup.sh
including vendor/cyanogen/vendorsetup.sh
}}}
The last line is important: {{{
$ cat vendor/cyanogen/vendorsetup.sh
add_lunch_combo cyanogen_ace-eng
add_lunch_combo cyanogen_bravo-eng
add_lunch_combo cyanogen_bravoc-eng
add_lunch_combo cyanogen_buzz-eng
add_lunch_combo cyanogen_dream_sapphire-eng
add_lunch_combo cyanogen_espresso-eng
add_lunch_combo cyanogen_glacier-eng
add_lunch_combo cyanogen_harmony-eng
add_lunch_combo cyanogen_hero-eng
add_lunch_combo cyanogen_heroc-eng
add_lunch_combo cyanogen_inc-eng
add_lunch_combo cyanogen_legend-eng
add_lunch_combo cyanogen_liberty-eng
add_lunch_combo cyanogen_one-eng
add_lunch_combo cyanogen_passion-eng
add_lunch_combo cyanogen_sholes-eng
add_lunch_combo cyanogen_supersonic-eng
add_lunch_combo cyanogen_vibrant-eng
add_lunch_combo cyanogen_vision-eng
add_lunch_combo cyanogen_z71-eng

PATH=$PATH:$PWD/vendor/cyanogen/tools ; export PATH
}}}
The output include the list of supported (by cyanogenmod) devices.
For instance if you have the Wildfire (codename 'buzz') phone do: {{{
lunch cyanogen_buzz-eng
}}}

Then build the source, backup what's on your device, including the operating system, and flash the new replicant image.

Then test what works and what doesn't.

The images are located in {{{
out/target/product/dream_sapphire
}}}
in the case of the HTC Dream. You need to look in the path that corresponds to your device.

Trying free replacements

The source code you just built contains some free replacements for the proprietary
libraries shipped by your phone vendor with the default firmware.

A list of proprietary libraries is available in {{{
device/htc/dream_sapphire/extract-files.sh
}}}
Note: don't run this file, just look at it. If you run it, the proprietary files will be copied from your phone into the build tree. A build containing proprietary files would put you and
your users at risk. Additionally, it is illegal to redistribute such build, because the libraries are not redistributable(the copyright owner didn't allow you to redistribute them).

=== RIL test ===
I will take the example of how to use the free RIL (Radio Interface Library) to see if it works fine without modifications:
The proprietary RIL library (which you don't have in the phone) location is found looking at the extract-files.sh
here's a part of extract-files.sh: {{{
adb pull /system/lib/libhtc_ril.so ../../../vendor/htc/$DEVICE/proprietary/libhtc_ril.so
}}}
Note: don't run this command, just look at it. If you run it, the proprietary files will be copied from your phone into the build tree. A build containing proprietary files would put you and
your users at risk. Additionally, it is illegal to redistribute such build, because the libraries are not redistributable(the copyright owner didn't allow you to redistribute them).

So looking at the above line the proprietary RIL is located here on the phone: {{{
/system/lib/libhtc_ril.so
}}}
while the free ril is located here (known fact): {{{
/system/lib/libreference-ril.so
}}}
In order to test the free RIL you could be tempted to do that: {{{
  1. ./adb remount
  2. ./adb shell
    mv /system/lib/libreference-ril.so /system/lib/libhtc_ril.so
    }}}
    But that wouldn't work as it wouldn't be using the right serial port, the correct way to try that is to use getprop/setprop: {{{
  3. ./adb shell
  4. setprop
    usage: setprop <key> <value>
    }}}
    What you can do to set the libre RIL is - possibly - this: {{{
    ./adb shell
    setprop rild.libpath /system/lib/libreference-ril.so
    setprop rild.libargs -d/dev/smd0
    }}}
    Here's how it looks on a working replicant on the HTC Dream: {{{
  5. ./adb shell
  6. getprop | grep ril
    [ro.ril.hsxpa]: [2]
    [ro.ril.gprsclass]: [10]
    [rild.libpath]: [/system/lib/libreference-ril.so]
    [rild.libargs]: [-d/dev/smd0]
    [init.svc.ril-daemon]: [running]
    [ro.ril.def.agps.mode]: [2]
    [gsm.version.ril-impl]: [android reference-ril 1.0]
    }}} * /dev/smd0 is the (emulated) serial port * /system/lib/libreference-ril.so is where to look for the RIL hardware specific library

Then, you can kill the ril daemon: {{{
./adb shell killall rild
}}}
Then try the reference RIL. You can see debugging things and such by doing: {{{
./adb logcat -b radio
}}}

That's also tested and worked on the gtklocker's HTC Hero, so I suppose it will work for the most HTC devices out there. If your device isn't listed anywhere, don't dare to try it.

Replacing proprietary libraries for real

On the HTC Dream the following proprietary libraries were replaced:
(Refer to [wiki:ProprietaryHtcDreamLibsReplacement] for more up to date details(or fix it if it's less recent))

The first thing you will have to do is to modify the build system.
The key thing to do is to change

=== RIL ===
If the RIL you previously tried works fine, why not switching to it...directly in the build system.
Here's the diff between A working RIL and a non-working RIL for the htcdream: {{{
android_device_htc_dream_sapphire$ git diff 5593d2899203ec378c306701788f1c43af9a6935 -- full_dream_sapphire.mk
diff --git a/full_dream_sapphire.mk b/full_dream_sapphire.mk
index 9ec7feb..eb1b956 100644
--- a/full_dream_sapphire.mk
+++ b/full_dream_sapphire.mk
@ -40,7 +40,8 @ PRODUCT_PROPERTY_OVERRIDES := \
ro.media.dec.jpeg.memcap=10000000

PRODUCT_PROPERTY_OVERRIDES = \
-    rild.libpath=/system/lib/libhtc_ril.so \
    rild.libpath=/system/lib/libreference-ril.so \
+    rild.libargs=-d/dev/smd0 \
     wifi.interface=tiwlan0
  1. Time between scans in seconds. Keep it high to minimize battery drain.

}}}
Note that full_dream_sapphire.mk is located here: {{{
device/htc/dream_sapphire/full_dream_sapphire.mk
}}}
The diff is self-explanatory and how to do the change is left as an exercise to the reader.

In case the RIL need to be modified the sources are in : {{{
hardware/ril/reference-ril
}}}
They are written in C.

=== Audio libraries ===
On the HTC dream the audio libraries were modified.
If your device is an msm7k "CPU" (in reality it's called a SOC, or system on a chip), it already contain [http://gitorious.org/replicant/android_hardware_msm7k/commit/e0b55a19b2fc004915503ebdfd7c4c02c4264611 the routing fix].
Note several things on [http://gitorious.org/replicant/android_hardware_msm7k/commit/e0b55a19b2fc004915503ebdfd7c4c02c4264611 the commit]: * the routing was disabled, I had to re-enable it * I had to replace some non-existant functions, for that I used public playwav2.c source code that the author released to us under the apache 2.0 license. * I had nearly no knowledge of C++ * it was easy

Re-using source code
The previous source code re-used some public source code that was licensed under the Apache 2.0 license.
The ril will also re-use some public source code licensed under Apache 2.0.
That is the advised way to do it as it save some time and is easier to do, however proper credit must be attributed, at least in the commit message.
It is even advised to look at the public apache 2.0 source code of other rils libraries or components of android.

=== Ril === * vilvord ril * openmoko (android on freerunner) ril

Source organization and commit access
Until now we made some changes in the tree, but we want the changes to land upstream in replicant.
For instance let's say we modified only the ril path like in the ril section in {{{
device/htc/dream_sapphire/full_dream_sapphire.mk
}}}
first we save our modifications: {{{
cd device/htc/dream_sapphire/
git diff > git_diff.patch
}}}
then we find where is the root of the git repository we are in: {{{
cd replicant-2.2 #top replicant directory where everything is in
cd .repo
cat manifest.xml
}}}
and we find that: {{{
<project path="device/htc/buzz" name="CyanogenMod/android_device_htc_buzz" remote="github" />
}}}
so...now our repository is in device/htc/buzz
We will now look where the source repository is: {{{
cd device/htc/buzz
cd .git
cat config
}}}
We find that: {{{
url = git://github.com/CyanogenMod/android_device_htc_buzz.git
}}}

Then create a directory, not under the replicant-2.2 directory that will contain your repositories: {{{
mkdir repo
cd repo
}}}
and clone the source: {{{
git clone git://github.com/CyanogenMod/android_device_htc_buzz.git
cd android_device_htc_buzz
}}}
apply the previous patch: {{{
git apply path/to/git_diff.patch
}}}
commit locally the result: {{{
git commit -s
}}}
Note that the commit message should have the following format:
The first line should be a summary
Followed by a linebreak
And then the details explaining the commit
If you made an error writing the commit message do {{{
git commit --amend
}}}

TODO: complete for sending the git patch(git format-patch -1,git send-email)

==== Pushing to replicant ====
TODO: git remote add+git push