python - 转换 mmap 对象(mmaps 不支持串联)/将 c 代码转换为 python

Question

大家好，我正在尝试将下面的代码转换为 python(访问树莓派 1Mhz 计时器)，我不知道什么时候要映射对象，我们需要 + TIMER_OFFSET (timer = (long long int *) ((char *)st_base + TIMER_OFFSET);) 当我尝试在 Python 中执行此操作时，我得到了 SystemError: mmaps don't support concatenation。我一直在寻找转换 mmap 对象，但我什么也没找到，我们可以解决这个问题吗？可以将整个代码转换为 python 吗？我的意思是现在我对它有了第二个想法？

#include <stdio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#define ST_BASE (0x3F003000)
#define TIMER_OFFSET (4)

int main(int argc, char *argv[]) {
    long long int t, prev, *timer; // 64 bit timer
    int fd;
    void *st_base; // byte ptr to simplify offset math

    // get access to system core memory
    if (-1 == (fd = open("/dev/mem", O_RDONLY))) {
        fprintf(stderr, "open() failed.\n");
        return 255;
    }

    // map a specific page into process's address space
    if (MAP_FAILED == (st_base = mmap(NULL, 4096,
                        PROT_READ, MAP_SHARED, fd, ST_BASE))) {
        fprintf(stderr, "mmap() failed.\n");
        return 254;
    }

    // set up pointer, based on mapped page
    timer = (long long int *)((char *)st_base + TIMER_OFFSET); //<- here is problem

    // read initial timer
    prev = *timer;
    // and wait
    sleep(1);

    while (1==1) { // forever
        // read new timer
        t = *timer;
        printf("Timer diff = %lld    \r", prev);
        fflush(stdout);
        // save current timer
        prev = t;
        // and wait
        sleep(1);
    }
    // will never get here
    return 0;
}

Python 代码(现在我跳过这个 ifs):

ST_BASE = 0x3F003000
TIMER_OFFSET = 4
import struct
sizeof_long_long = struct.calcsize('q')

def timer():
    while True:
        fd = os.open("/dev/mem",os.O_RDWR | os.O_SYNC)
        stBase = mmap.mmap(fileno=fd,length=4096,offset=ST_BASE)
        timer_bytes = stBase[TIMER_OFFSET:TIMER_OFFSET + sizeof_long_long]
        #print(timer_bytes)
        timer_value, = struct.unpack('q', timer_bytes)
        print(timer_value)
        os.close(fd)

Answer 1

差不多好了 :) 只需 unpack_from 而不是 off unpack

import os, mmap, sys
import struct

ST_BASE = 0x3F003000
TIMER_OFFSET = 4
sizeof_long_long = struct.calcsize("Q")
LENGTH = TIMER_OFFSET + sizeof_long_long

def timer():
    fd = os.open("/dev/mem", os.O_RDONLY | os.O_SYNC)
    stBase = mmap.mmap(fileno=fd, length=4096, access=mmap.ACCESS_COPY, offset=ST_BASE)
    os.close(fd)

    while True:
        timer_value = struct.unpack_from("Q", stBase, TIMER_OFFSET)[0]
        print("timer_value")