1. Download and install toolchain
$ curl https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.3.0-2019.08.0-x86_64-linux-ubuntu14.tar.gz
2. Download and install J-Link Software Documentation Pack
https://www.segger.com/downloads/jlink/
$ sudo apt install JLink_Linux_V656b_x86_64.deb
3. Configure and build NuttX
$ mkdir ./nuttx; cd ./nuttx
$ git clone https://github.com/apache/incubator-nuttx.git
$ git clone https://github.com/apache/incubator-nuttx-apps.git
$ cd nuttx
$ make distclean
$ ./tools/configure.sh hifive1-revb:nsh
$ make V=1
4. Flash the nuttx with J-Link and run
$ picocom -b 115200 /dev/ttyACM0
$ /opt/SEGGER/JLink_V656b/JLinkGDBServer -device FE310
$ riscv64-unknown-elf-gdb ./nuttx
(gdb) target extended-remote:2331
(gdb) load nuttx
(gdb) c
5. TODO
Support GPIO/SPI/I2C/RTC/WDT/PWM
Support RISC-V User mode
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