:add lab7 spoc exercise related codes

related_info/lab7/software-hardware-locks/yield.s

@@ -0,0 +1,29 @@
+.var mutex
+.var count
+
+.main
+.top	
+
+.acquire
+mov  $1, %ax        
+xchg %ax, mutex     # atomic swap of 1 and mutex
+test $0, %ax        # if we get 0 back: lock is free!
+je .acquire_done    
+yield               # if not, yield and try again
+j .acquire
+.acquire_done
+
+# critical section
+mov  count, %ax     # get the value at the address
+add  $1, %ax        # increment it
+mov  %ax, count     # store it back
+
+# release lock
+mov  $0, mutex
+
+# see if we're still looping
+sub  $1, %bx
+test $0, %bx
+jgt .top	
+
+halt