On Tue, Mar 06, 2012 at 03:01:50PM +0100, Florian Fainelli wrote: > > hi all: > > I have some questions about mips_hpt_frequency: > > 1. is mips_hpt_frequency == mips cpu frequency? > > No, it is usually cpu frequency / 2. The architecture specification leaves the counter clock rate up up to the implementation and only says the clock rate is a function of the pipeline clock. In all reality this means the counter is running at the full or half frequency. Just don't build on it, clock := pipeline_clock * next_weeks_lottery_number % 42 would by compliant ;-) On some CPUs the frequency can even be selected through a configuration bitstream at reset time so you can't always count on a fixed relation between CPU clock and count rate. Some older CPU manuals contain a confusing wording saying the counter increments at half (or full) instruction issue rate. That just means the pipeline clock, no reason to be confused. Ralf
