-set RTTC_RTMR [expr $AT91C_BASE_RTTC + 0x00]
-set RTTC_RTAR [expr $AT91C_BASE_RTTC + 0x04]
-set RTTC_RTVR [expr $AT91C_BASE_RTTC + 0x08]
-set RTTC_RTSR [expr $AT91C_BASE_RTTC + 0x0c]
+set RTTC_RTMR [expr {$AT91C_BASE_RTTC + 0x00}]
+set RTTC_RTAR [expr {$AT91C_BASE_RTTC + 0x04}]
+set RTTC_RTVR [expr {$AT91C_BASE_RTTC + 0x08}]
+set RTTC_RTSR [expr {$AT91C_BASE_RTTC + 0x0c}]