--- /sys/src/9/pc/sdata.c
+++ /sys/src/9/pc/sdata.c
@@ -1496,8 +1496,10 @@ atagenio(Drive* drive, uchar* cmd, int clen)
 {
 	uchar *p;
 	Ctlr *ctlr;
-	vlong lba, len;
-	int count, maxio;
+	int maxio;
+	ulong count;
+	vlong len;
+	uvlong lba;
 
 	/*
 	 * Map SCSI commands into ATA commands for discs.
@@ -1603,17 +1605,11 @@ atagenio(Drive* drive, uchar* cmd, int clen)
 	}
 
 	ctlr = drive->ctlr;
-	if(clen == 16){
+	if(clen == 16)
 		/* ata commands only go to 48-bit lba */
 		if(cmd[2] || cmd[3])
 			return atasetsense(drive, SDcheck, 3, 0xc, 2);
-		lba = (uvlong)cmd[4]<<40 | (uvlong)cmd[5]<<32;
-		lba |= cmd[6]<<24 | cmd[7]<<16 | cmd[8]<<8 | cmd[9];
-		count = cmd[10]<<24 | cmd[11]<<16 | cmd[12]<<8 | cmd[13];
-	}else{
-		lba = cmd[2]<<24 | cmd[3]<<16 | cmd[4]<<8 | cmd[5];
-		count = cmd[7]<<8 | cmd[8];
-	}
+	scsilbacount(cmd, clen, &lba, &count);
 	if(drive->data == nil)
 		return SDok;
 	if(drive->dlen < count*drive->secsize)