UART RX implementation on PIC32 devices

[francois-berder]

Contribution description

This PR finally implements UART RX on PIC32 devices and makes it possible to run examples/default on pic32-clicker and pic32-wifire.

GPIO

Have a look at PR #12475. GPIOs are now working very similarly that on STM32.

Interrupts

Interrupts were refactored: we assume devices use EIC (that is true since Malta board was removed from RIOT) and the implementation is similar to RISCV FE310 CPU EIC.
I also found out that updating the MIPS toolchain completely broke interrupts due to a missing file (mips_excpt_isr.S) in 2018.09-03 that used to be present in 2016.05-03 version. So mips_excpt_isr.S is now present in cpu/misp32r2_common.

UART

UART peripheral driver was also refactored to make it more similar to STM32 UART driver implementation. UART configuration is now defined in board periph_conf.h file.
The major novelty of this PR is that is now possible to receive data over serial.

miscellaneous

pm_reboot was implemented in cpu/mips_pic32_common such that all commands available when running examples/default are now working on pic32-clicker and pic32-wifire.

Testing procedure

I ran examples/default and checked that I could execute commands on pic32-clicker and pic32-wifire.

Issues/PRs references

Depends on #12475.

[francois-berder]

This PR is now ready for review.
@benpicco Could you remove the "waiting for other PR" label ?

[francois-berder]

Interestingly, a previous murdock build revealed that MIPS toolchain uses a different type for size_t than other embedded toolchains.

$ echo | gcc -E -xc -include 'stddef.h' - | grep size_t
typedef long unsigned int size_t;
$ echo | arm-none-eabi-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | avr-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | mips-mti-elf-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef long unsigned int size_t;
$ echo | msp430-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | riscv-none-embed-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | xtensa-esp32-elf-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | xtensa-esp8266-elf-gcc -E -xc -include 'stddef.h' - | grep size_t
typedef unsigned int size_t;
$ echo | clang -E -xc -include 'stddef.h' - | grep size_t
typedef long unsigned int size_t;

Operating System Environment
-----------------------------
         Operating System: "Ubuntu" "18.04.4 LTS (Bionic Beaver)"
                   Kernel: Linux 5.3.0-28-generic x86_64 x86_64
             System shell: /bin/dash (probably dash)
             make's shell: /bin/dash (probably dash)

Installed compiler toolchains
-----------------------------
               native gcc: gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0
        arm-none-eabi-gcc: arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 8-2019-q3-update) 8.3.1 20190703 (release) [gcc-8-branch revision 273027]
                  avr-gcc: avr-gcc (GCC) 5.4.0
         mips-mti-elf-gcc: mips-mti-elf-gcc (Codescape GNU Tools 2018.09-03 for MIPS MTI Bare Metal) 6.3.0
               msp430-gcc: msp430-gcc (GCC) 4.6.3 20120301 (mspgcc LTS 20120406 unpatched)
     riscv-none-embed-gcc: riscv-none-embed-gcc (GNU MCU Eclipse RISC-V Embedded GCC, 64-bit) 8.2.0
     xtensa-esp32-elf-gcc: xtensa-esp32-elf-gcc (crosstool-NG crosstool-ng-1.22.0-80-g6c4433a5) 5.2.0
   xtensa-esp8266-elf-gcc: xtensa-esp8266-elf-gcc (crosstool-NG crosstool-ng-1.22.0-80-g6c4433a5) 5.2.0
                    clang: clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)

Installed compiler libs
-----------------------
     arm-none-eabi-newlib: "3.1.0"
      mips-mti-elf-newlib: "2.5.0"
  riscv-none-embed-newlib: "3.0.0"
  xtensa-esp32-elf-newlib: "2.2.0"
xtensa-esp8266-elf-newlib: "2.2.0"
                 avr-libc: "2.0.0" ("20150208")

Installed development tools
---------------------------
                   ccache: ccache version 3.4.1
                    cmake: cmake version 3.10.2
                 cppcheck: Cppcheck 1.82
                  doxygen: 1.8.13
                      git: git version 2.17.1
                     make: GNU Make 4.1
                  openocd: Open On-Chip Debugger 0.10.0
                   python: Python 2.7.17
                  python2: Python 2.7.17
                  python3: Python 3.6.9
                   flake8: 3.5.0 (mccabe: 0.6.1, pycodestyle: 2.3.1, pyflakes: 1.6.0) CPython 3.6.9 on Linux
               coccinelle: spatch version 1.0.4 with Python support and with PCRE support

[francois-berder]

In the last Murdock build, all lwip related tests failed because it could not clone lwip repository. However, I was able to do it on my machine.

[aabadie]

This is a major refactoring and unfortunately, I don't have the hardware to test this.

I have a couple of comments regarding the changes related to the build system.

[francois-berder]

This is a major refactoring and unfortunately, I don't have the hardware to test this.

Indeed but I could split this PR in several parts:

1. EIC refactoring
2. UART refactoring
3. pm_reboot implementation for PIC32 devices

Let me know what is preferred.

Concerning the lack of hardware, I do have a spare WiFire board. Send me an email if you are interested.

[aabadie]

@francois-berder, I can't test this PR and I don't who is able to test except you. If you could paste the output of the build/flash/term of example/default, call help, reboot, that would be enough for me to merge this PR.

[francois-berder]

In this case, here are some logs for both clicker and wifire:
build-clicker.log
build-wifire.log
term-clicker.log
term-wifire.log

[aabadie]

All good from my side. Thanks for providing the output @francois-berder !

ACK and go!