Due MONDAY November 30, 1998
Problem 1: Error Coding
A Hamming SEC code includes 11 data bits and 4 check bits according to the below table:
| d11 | d10 | d9 | d8 | d7 | d6 | d5 | c4 | d4 | d3 | d2 | c3 | d1 | c2 | c1 | |
| S4 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| S3 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 |
| S2 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 |
| S1 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 |
What are the syndrome equations?
Problem 2:
Which of the following two approaches to spin locks will result in better overall system performance, and why? Assume that you are running on a system which has 16 single-CPUscalar-issue processor boards plugged into a backplane. Each processor has its own cache, with snoopy coherence done over the single shared bus with sequential consistency. Both routines use a common test_and_set subroutine as follows:
int test_and_set(volatile int *addr)
{ /* sets address to 1, returns previous value
* 1 is locked, 0 is written elsewhere to free lock
*/
int old_value;
old_value = swap_atomic(addr, 1);
return(old_value); }
Approach 1:
void lock_a(volatile int *lock_status)
{ while (test_and_set(lock_status) == 1); }
Approach 2:
void lock_b(volatile int *lock_status)
{ while (test_and_set(lock_status) == 1)
{ while (*lock_status) == 1); }
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