> > > > -#define COUNT_TO_USEC(x) ((x) * 16 / 133) > > > > +#define COUNT_TO_USEC(x) ((x) / 133 * 16) > > > > > > Before the change, the result is useful for all values of x in the > > > interval from 0 through UINT_MAX/16 = 268435455 = 268 seconds, i. e. > > > for all values that make sense to be measured in microseconds. > > > > We're actually discussing this elsewhere. I don't have > > permission to paste the other side of the conversation, but > > I can show you my calculations: > > > > > The original implementation is fine until we reach 32.28 seconds, which > > > as you predicted is 0x1000_0000: > > > > > 0x10000000 * PRESCALER) / (CLOCK_SPEED_133_MHZ) > > > (268435456 * 16 ) / (133 * 1000 * 1000) == 32.28 seconds > > > > > If we spend >30 seconds at the u-boot commandline, which is not > > > unreasonable by any stretch, then the kernel assumes responsibility for > > > the remaining of the time spent at the prompt, which is obviously not > > > acceptable for this usecase. > > This makes no sense to me. An overflow will not happen before > UINT_MAX/16 = 268435455 = 268 seconds.
Right, but that's the timer. The issue here is not that the timer is overflowing, it's the arithmetics that takes place once the timer value is obtained. If a value of >0x10000000 is read, then we carry out the arithmetic above, then other registers overflow. > Anyway. If you have overflof problems, then use proper arithmetics. > > > > If you need a bigger number range, then use proper arithmetics. It';s > > > available, just use it. > > > > Would you be able to lend a hand here, as I'm no mathematician? > > > > What are the correct arithmetics? > > There are routines like do_div() or lldiv() etc. that can be used when > 32 bit arithmetics is really not good enough. Ah ha, thanks. > However, I fail to see why that should even be needed here. As above. -- Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
