debug/programs/multicore.c

   1 #include <stdint.h>
   2
   3 typedef struct {
   4     int counter;
   5 } atomic_t;
   6
   7 static inline int atomic_xchg(atomic_t *v, int n)
   8 {
   9     register int c;
  10
  11     __asm__ __volatile__ (
  12             "amoswap.w.aqrl %0, %2, %1"
  13             : "=r" (c), "+A" (v->counter)
  14             : "r" (n));
  15     return c;
  16 }
  17
  18 #define csr_read(csr)                                   \
  19 ({                                                      \
  20     register unsigned long __v;                         \
  21     __asm__ __volatile__ ("csrr %0, " #csr              \
  22                   : "=r" (__v));                        \
  23     __v;                                                \
  24 })
  25
  26 static inline void mb(void)
  27 {
  28     __asm__ __volatile__ ("fence");
  29 }
  30
  31 void get_lock(atomic_t *lock)
  32 {
  33     while (atomic_xchg(lock, 1) == 1)
  34         ;
  35     mb();
  36 }
  37
  38 void put_lock(atomic_t *lock)
  39 {
  40     mb();
  41     atomic_xchg(lock, 0);
  42 }
  43
  44 static atomic_t buf_lock = { .counter = 0 };
  45 static char buf[32];
  46 static int buf_initialized;
  47 static unsigned hart_count[2];
  48
  49 static const char case_bit = 'a' - 'A';
  50 volatile int initialized;
  51
  52 int main()
  53 {
  54     uint32_t hartid = csr_read(mhartid);
  55     hart_count[hartid] = 0;
  56
  57     while (1) {
  58         get_lock(&buf_lock);
  59         hart_count[hartid]++;
  60
  61         if (!buf_initialized) {
  62             for (unsigned i = 0; i < sizeof(buf); i++) {
  63                 buf[i] = 'A' + (i % 26);
  64             }
  65             buf_initialized = 1;
  66         }
  67
  68         char first = buf[0];
  69         int offset = (first & ~0x20) - 'A';
  70         for (unsigned i = 0; i < sizeof(buf); i++) {
  71             while (buf[i] != (first - offset + ((offset + i) % 26)))
  72                 ;
  73
  74             if (hartid & 1)
  75                 buf[i] = 'A' + ((i + hartid + hart_count[hartid]) % 26);
  76             else
  77                 buf[i] = 'a' + ((i + hartid + hart_count[hartid]) % 26);
  78         }
  79         put_lock(&buf_lock);
  80     }
  81 }