--hfa-options Set hashfast options name:clock@voltage0@voltage1@voltage2@voltage3:clk0:clk1:clk2:clk3

This command allows you to set options for each discrete hashfast device by
its name (if the firmware has naming support, i.e. version 0.3+). Currently
this takes as option the clock speed, 4 voltages and 4 clock offsets (voltage and
clock offset for each of the 4 cores of the ASIC)
e.g.:
--hfa-options "rabbit:650,turtle:550@800,bee:950@905@925@975@985:-100:-50:0:25"

Would set a device named rabbit to clock speed 650 MHz using default voltage, the
one named turtle to 550 MHz using a voltage of 800 mV for all cores and the one
named bee is set with different clock and voltage for each ASIC core as following:
> core 0 at 850 MHz (950 MHZ base clock with -100 MHz clock offset) and voltage of 905mV
> core 1 at 900 MHz (950 MHZ base clock with -50 MHz clock offset) and voltage of 925mV
> core 2 at 950 MHz (950 MHZ base clock with 0 MHz clock offset) and voltage of 975mV
> core 3 at 975 MHz (950 MHZ base clock with 25 MHz clock offset) and voltage of 985mV
Starting the device at a speed where it is most stable will give more reliable
hashrates long term and prevent it interacting with other devices, rather than
depending on the clockdown feature in cgminer.

Note: Setting voltage may cause a board reset and hotplug event on cgminer startup.