[Simh] Losing Time In SIMH

[Sergey Oboguev]

It has been a long while since I touched SIMH, but when I did in the 3.9.x timeframe (and I do not know if the design has changed since then), I made the following note:

... the tendency of SIMH idea of system time (such as OpenVMS system time, when OpenVMS is executed on SIMH) to fall behind wall clock time. This “falling behind” happens because of a number of [...] reasons: host timer events are fired later then requested; it takes time for the hibernating thread to resume and start tracking time; accumulating rounding errors in time data obtained from the host, SIMH timing mechanisms dependence on the VCPU calibration (i.e. instructions per second rate) which is subject to variations because of a concurrent host load and also inherently – because of the inherent variations in the composition of the executed instruction set, page faults, synchronous IO operations executed on the VCPU thread etc.; because of OpenVMS suspension while SIMH console is in use or ROM console is in use; because of OpenVMS suspension while host system was suspended and similar reasons.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.trailing-edge.com/pipermail/simh/attachments/20170131/75098ad2/attachment.html>