Look in /nvram.
 [rsc] --rw-rw-r-- M 1428987 glenda sys 8809 Jan 28 12:26 sys/src/libauthsrv/readnvram.c
	/n/sourcesdump/2006/0128/plan9/sys/src/libauthsrv/readnvram.c:40,45 - 
	/n/sourcesdump/2006/0129/plan9/sys/src/libauthsrv/readnvram.c:40,46
	  	"mips", "#r/nvram", 1024+900, sizeof(Nvrsafe),
	  	"power", "#F/flash/flash0", 0x440000, sizeof(Nvrsafe),
	  	"power", "#r/nvram", 4352, sizeof(Nvrsafe),	/* OK for MTX-604e */
	+ 	"power", "/nvram", 0, sizeof(Nvrsafe),	/* OK for Ucu */
	  	"debug", "/tmp/nvram", 0, sizeof(Nvrsafe),
	  };