linux - OMAP5432 evm 处理器时钟周期

Question

我正在为 OMAP5432 (Cortex A15) 编写一个 linux 驱动程序，它将处理器周期计数器值读取到每个 IRQ。计数器初始化如下：

static inline void init_perfcounters(int32_t do_reset, int32_t enable_divider) 
{
    // in general enable all counters (including cycle counter)
    int32_t value = 1;

    // peform reset:
    if (do_reset) {
        value |= 2;     // reset all counters to zero.
        value |= 4;     // reset cycle counter to zero.
    }

    if (enable_divider)
        value |= 8;     // enable "by 64" divider for CCNT.

    value |= 16;

    // program the performance-counter control-register:
    asm volatile ("MCR p15, 0, %0, c9, c12, 0\t\n" :: "r"(value));

    // enable all counters:
    asm volatile ("MCR p15, 0, %0, c9, c12, 1\t\n" :: "r"(0x8000000f));

    // clear overflows:
    asm volatile ("MCR p15, 0, %0, c9, c12, 3\t\n" :: "r"(0x8000000f)); 
}

分频器被禁用。Linux 内核是 4.0，频率缩放选项被禁用，只有 1 个 CPU 正在运行。我每秒都有一个 IRQ，我读到这样的值：

static inline unsigned int get_cyclecount(void)
{
  unsigned int value;

  // Read CCNT Register
  asm volatile ("MRC p15, 0, %0, c9, c13, 0\t\n": "=r"(value));  
  return value;
}

我不明白为什么两个 IRQ 之间的周期数约为 20M，而处理器应该以 2GHz 运行。有人有想法么 ？

先感谢您。