#define RT_HW_HEAP_BEGIN (void*)&__bss_end
    #define RT_HW_HEAP_END (void*)(RT_HW_HEAP_BEGIN + 64 * 1024 * 1024)

    char *p = rt_malloc(60000 * 28 * 28);
    rt_kprintf("rt_malloc done\n");
    rt_thread_mdelay(500);
    int cnt = 0;
    for (int i = 0; i < 60000 * 28 * 28; ++i) {
        p[i] = (char)i;
        if (cnt++ > 1000) {
            rt_kprintf("%d\n", i);
            cnt = 0;
        }
    }