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
