/* * 24K Erratum 48: Lost Data on Stores During Refill. Problem: The FSB (fetch store buffer) acts as an intermediate buffer for the data cache refills and store data. The following describes the scenario where the store data could be lost. * A data cache miss, due to either a load or a store, causing fill data to be supplied by the memory subsystem * The first three doublewords of fill data are returned and written into the cache * A sequence of four stores occurs in consecutive cycles around the final doubleword of the fill: * Store A * Store B * Store C * Zero, One or more instructions * Store D The four stores A-D must be to different doublewords of the line that is being filled. The fourth instruction in the sequence above permits the fill of the final doubleword to be transferred from the FSB into the cache. In the sequence above, the stores may be either integer (sb, sh, sw, swr, swl, sc) or coprocessor (swc1/swc2, sdc1/sdc2, swxc1, sdxc1, suxc1) stores, as long as the four stores are to different doublewords on the line. If the floating point unit is running in 1:2 mode, it is not possible to create the sequence above using only floating point store instructions. In this case, the cache line being filled is incorrectly marked invalid, thereby losing the data from any store to the line that occurs between the original miss and the completion of the five cycle sequence shown above. * Run the data cache in write-through mode. * Insert a non-store instruction between Store A and Store B or Store B and Store C. */