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问题:

When I try to build for Raspberry Pi2, the option is raspi-2, right?

$ gyp_cobalt raspi-2

$ ninja -C out/raspi-2_debug cobalt

回答1:

There currently is no raspi-2 configuration, but the raspi-1 configuration will run on a Raspberry Pi Zero, 1, 2, and 3. It won't take advantage of the Neon instruction set available on a Raspberry Pi 2, but it will run. Both the Broadcom 2835 (RasPi 0,1) and 2836 (RasPi 2) are 32-bit ARM chips, so binaries compiled to a common subset of the instruction set should run on both devices.

Creating a raspi-2 configuration wouldn't be too difficult.

$ cd src/starboard/raspi
$ cp -R 1/ 2

And modify src/starboard/rapi/2/gyp_configuration.gypi and src/starboard/rapi/2/gyp_configuration.py to refer to 'raspi-2' where they refer to 'raspi-1'.

Then one could furthet modify gyp_configuration.gypi to pass in more appropriate compiler flags for a Raspberry Pi 2. One might also want to set these properties, to enable Neon assembly optimizations in libwebp:

'arm_version': 7,
'armv7': 1,
'arm_neon': 1,

回答2:

Thanks. I put it all together.

    $ cd ~/
    $ git clone https://cobalt.googlesource.com/cobalt
    $ cd cobalt/src/startboard/raspi
    $ cp -R 1/ 2
    $ cd 2/
    $ vi gyp_configuration.gypi

Edit line 37-40 and change rasp-1 to rasp-2 at line 167-180.

    # RasPi 2 is ARMv7
    'arm_version': 7,
    'armv7': 1,
    'arm_neon': 1,

    ....

    'default_configuration': 'raspi-2_debug',
    'configurations': {
      'raspi-2_debug': {
        'inherit_from': ['debug_base'],
      },
      'raspi-2_devel': {
        'inherit_from': ['devel_base'],
      },
      'raspi-2_qa': {
        'inherit_from': ['qa_base'],
      },
      'raspi-2_gold': {
        'inherit_from': ['gold_base'],
      },

Then,

    $ vi gyp_configuration.py

Edit line 14 and change rasp-1 to rasp-2 at line 25.

    """Starboard Raspberry Pi 2 platform configuration for gyp_cobalt."""

    ....

    return _PlatformConfig('raspi-2')

Then, set $RASPI_HOME like the description of a manual.

    $ export RASPI_HOME=~/raspi-tools
    $ cd ~/cobalt/src/
    $ cobalt/build/gyp_cobalt raspi-2
    $ ls out/
    ./
    ../
    raspi-2_debug/
    raspi-2_devel/
    raspi-2_gold/
    raspi-2_qa/
    $ ninja -C out/raspi-2_debug cobalt

But clang++ command is not found. And there is not llvm-build in the following path