If you’re an Arduino IDE user, we’ve released v1.0.2 of the Board Support Package.
If you’ve already installed earlier versions, you should see an “Update” button when you do Tools-> Boards-> Board Manager and search for the SiFive boards.
What’s changed?
Updated OpenOCD to make uploading more reliable
Updated the version of GDB to allow debugging ‘C’ extension programs.
Cleaned up the delay(), millis(), and micros() functions to be more efficient and avoid glitches.
Added a ~320MHz clock option for the HiFive1
Fixed issues uploading to the Arty Dev Kit Board.
You can browse or contribute to the the source code here:
Note that the PLL is only rated to 384Mhz and we only qualified the boards at +320MHz. If you try to program something the board can’t handle, you’ll probably need to use the “safe” bootloader to recover, so you should learn to use it before going nuts with the clock rate.
The problem with just using those to change the clock is that the rest of the Arduino code needs F_CPU for UART Baud Rate, delay(), etc, so redefining this is the most reliable way to play with this in Arduino-land. See:
(on linux, this is placed in ~/.arduino15/packages/sifive when you download the package).