[U-Boot-Users] about embedded assembly

hello,all The following program is from MARVELL U-Boot

if(mvCtrlModelGet() == MV_5281_DEV_ID) /* Orion 2 */ { __asm__ __volatile__("mrc p15, 0, %0, c14, c0, 0" : "=r" (temp):: "memory"); if (temp & 0x10000000) { printf("CPU: Write allocate enabled\n"); } else { printf("CPU: Write allocate Disabled\n"); } }

I don't understand what's the following sentense mean,please detailed explain it,thanks

__asm__ __volatile__("mrc p15, 0, %0, c14, c0, 0" : "=r" (temp):: "memory");

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