Add experimental GCC ARM toolchain

[xiongyihui]

To support GCC ARM toolchain:

1. convert some attributes

   • __weak to __attribute__((weak))

   • __forceinline to inline __attribute__((always_inline))

   • __packed to __attribute__((__packed__)), also need to change its location, for example

     convert __packed struct { char a; int b; } c; to struct __attribute__((__packed__)) { char a; int b; } c;.
     it is used by USB stack

2. wide character array defined by L"a wide string"

   By default, gcc uses 4 bytes to store a wide char, while armcc uses 2 bytes. In order to be compatible with armcc, add -fshort-wchar to gcc compiler flags.

3. convert asm code

Right now, it work partially. To test it.

rm source/daplink/interface/SVC_Table.s
progen generate -f projects.yaml -p lpc11u35_archble_if_bm -t make_gcc_arm
cd projectfiles/make_gcc_arm/lpc11u35_archble_if_bm
make

[xiongyihui]

@0xc0170 Do you have any idea that the gccarm firmware shows an empty disk? Which part of code is related?

[brianesquilona]

@0xc0170 Do you have any idea that the gccarm firmware shows an empty disk? Which part of code is related?

@xiongyihui you might want to check all msc related codes in source/usb.

[xiongyihui]

I figured out the issue. It is that cfgrom and cfgram are not configured at the linker script.

[xiongyihui]

It seem armcc uses much less RAM and Flash than gccarm. LPC11U35 doesn't have enough to run the interface firmware compiled with gccarm, even if without RTX RTOS.
A workaround is to make target_device to a const variable

[flit]

See the latest on #197. I'm almost done with the official port to gcc. Very unfortunately coincidental timing between us! 😔 I do very much appreciate your collaborative interest and effort. If you'd like to help test my gcc port, this would be appreciated.

[xiongyihui]

I see. I will test that.

[0xc0170]

As these might not be related to GCC port, please send t hem separately or after GCC support lands on master.

[0xc0170]

@xiongyihui Thanks for the effort ! Please review and test https://github.com/flit/DAPLink/tree/feature/gcc