This README contains extended details about FPGA mining with cgminer


Icarus

There is a hidden option in cgminer when Icarus support is compiled in:

--icarus-timing <arg> Set how the Icarus timing is calculated - one setting/value for all or comma separated
           default       Use the default Icarus hash time (2.6316ns)
           short         Calculate the hash time and stop adjusting it at ~315 difficulty 1 shares (~1hr)
           long          Re-calculate the hash time continuously
           value         Specify the hash time in nanoseconds (e.g. 2.6316)

     Icarus timing is required for devices that do not exactly match a default Icarus Rev3 in
     processing speed
     If you have an Icarus Rev3 you should not normally need to use --icarus-timing since the
     default values will maximise the MH/s and display it correctly

     Icarus timing is used to determine the number of hashes that have been checked when it aborts
     a nonce range (including on a LongPoll)
     It is also used to determine the elapsed time when it should abort a nonce range to avoid
     letting the Icarus go idle, but also to safely maximise that time

     'short' or 'long' mode should only be used on a computer that has enough CPU available to run
     cgminer without any CPU delays (an active desktop or swapping computer would not be stable enough)
     Any CPU delays while calculating the hash time will affect the result
     'short' mode only requires the computer to be stable until it has completed ~315 difficulty 1 shares
     'long' mode requires it to always be stable to ensure accuracy, however, over time it continually
     corrects itself

     When in 'short' or 'long' mode, it will report the hash time value each time it is re-calculated
     In 'short' or 'long' mode, the scan abort time starts at 5 seconds and uses the default 2.6316ns
     scan hash time, for the first 5 nonce's or one minute (whichever is longer)

     In 'default' or 'value' mode the 'constants' are calculated once at the start, based on the default
     value or the value specified

     To determine the hash time value for a non Icarus Rev3 device or an Icarus Rev3 with a different
     bitstream to the default one, use 'long' mode and give it at least a few hundred shares, or use
     'short' mode and take note of the final hash time value (Hs) calculated
     You can also use the RPC API 'stats' command to see the current hash time (Hs) at any time

     The Icarus code currently only works with a dual FPGA device that supports the same commands as
     Icarus Rev3 requires and also is less than ~840MH/s and greater than 2MH/s
     If a dual FPGA device does hash faster than ~840MH/s it should work correctly if you supply the
     correct hash time nanoseconds value

     The timing code itself will affect the Icarus performance since it increases the delay after
     work is completed or aborted until it starts again
     The increase is, however, extremely small and the actual increase is reported with the
     RPC API 'stats' command (a very slow CPU will make it more noticeable)
     Using the 'short' mode will remove this delay after 'short' mode completes
     The delay doesn't affect the calculation of the correct hash time