When is it advisable to value inventory at lower of cost?

in case of market value is less than carrying amount but this is differ from standard to another for example Us.gaap said that we can make valuation for inventory as a comparisopn between market value and CRC and market value no way to be higher tham net realizable value or to be lower than nrv and the other point if we have loss as result of market value we can make wright up for this loss according ifrs but no permission to do it according us.gaap

The statement of financial position should be its cost as determined.