On 10/13/2014 04:24 AM, Sébastien Bourdeauducq wrote: > On 08/12/2014 05:32 PM, Robert Jordens wrote: >> n = core.coerce(1.2345*ns) # [n] = core.cycle >> for i in range(1000): >> core.delay(n) >> f = dds.coerce(345*MHz) >> t = dds.coerce(core.coerce(1000*n, to=ns)) >> phi = dds.coerce(f*t, to=rad) # [f*t] = dds.ftw*dds.cycle > > It's implementable right now as: > > # n is RTIO cycle count (dimensionless int64) > n = time_to_cycles(1.2345*ns) > > for i in range(1000): > # cycles_to_time is exact (uses rational arithmetic) > # compiler optimizes to "now += n" (int64 operation) > delay(cycles_to_time(n))
> # ftw is raw int32 frequency tuning word > ftw = self.dds.frequency_to_ftw(345*MHz) > > # f is exact (rational) frequency in Hz > f = self.dds.ftw_to_frequency(ftw) > > # phi is in turns, rational number > phi = 1000*cycles_to_time(n)*f Looks good! The numeric types do not seem to have units atached to them and no typechecking is done on the units level. Doing delay(dds.frequency_to_ftw(123*MHz)) would not fail/err. That is ok by me. > When running on the device (running on the host in the interpreter is > also possible), the transforms turn that into the following code before > passing it to py2llvm (with 1GHz RTIO and DDS clocks): > > now = int64(0) > n = int64(1) > for i in range(1000): > now += n > frequency_to_ftw_return = 1481763717 > ftw = frequency_to_ftw_return > ftw_to_frequency_return = ((ftw * Fraction(1000000000, 1)) / 4294967296) > f = ftw_to_frequency_return > phi = ((1000 * (n * Fraction(1, 1000000000))) * f) > > The obvious performance optimization here is to have the constant > folding transform work across statements. The llvm optimizer passes should be able to do that, right? > Since there is only one FUD sampling by the DDS chip every 8 RTIO/DDS > cycles, this phase difference computation is correct only if "now" is > increased by a multiple of 8 in the block of code. You mean a multiple of 8 in total after the loop? I would think it is correct in any case just that you can not change POW (correctly) if now.microcycle != 0. Having known phase even for the microcycles is valuable since then we can e.g. turn on and off a dds pulse with microcycle phase accuracy using the rf switches. Robert. _______________________________________________ ARTIQ mailing list https://ssl.serverraum.org/lists/listinfo/artiq
