1. Download and install toolchain and openocd-k210
$ 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. Build openocd-k210
$ git clone https://github.com/kendryte/openocd-kendryte
$ cd openocd-kendryte
$ ./bootstrap & ./configure & make
3. Configure and build NuttX
$ mkdir ./nuttx; cd ./nuttx
$ git clone https://bitbucket.org/nuttx/nuttx.git
$ git clone https://bitbucket.org/nuttx/apps.git
$ cd nuttx
$ make distclean
$ ./tools/configure.sh maix-bit:nsh
$ make V=1
4. Download and run the nuttx from SRAM (not SPI-Flash)
$ picocom -b 115200 /dev/ttyUSB0
$ sudo ./src/openocd -s ./tcl -f ./tcl/kendryte.cfg -m 0
$ riscv64-unknown-elf-gdb ./nuttx
(gdb) target extended-remote :3333
(gdb) load nuttx
(gdb) c
5. TODO
PLL setting (currently CPU clock freq is assumed to be 416MHz)
Boot from SPI-Flash
Support peripherals such as GPIO/SPI/I2C/...
Support FPU
Support RISC-V User mode
