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在python中使用ctypes和mmap进行c++代码转换

debian-jessie ctypes cython python-3.x c++

0

vivek patel · 技术社区 · 7 年前

int fd_vdma = open("/dev/mem", O_RDWR|O_SYNC);  // open uiox device for vdma access
    if (fd_vdma < 1) {
        printf("Invalid mem device file\n");
    }
    // mmap the vdma device for vdma access

    unsigned int *ptr_vdma;
    ptr_vdma = (unsigned int*)mmap(NULL, VDMA_MAP_SIZE,PROT_READ|PROT_WRITE, 
    MAP_SHARED, fd_vdma, VDMA_ADDR);
    printf("DMA 1 virtual address: 0x%08x \n",ptr_vdma);

    *(ptr_vdma+5) = FRBUF_ADDR_0;
    *(ptr_vdma+7) = 2;  // use internal fifos to trigger xfer
    *(ptr_vdma+8) = 20480;
    *(ptr_vdma+6) = (75 << 16) + (HORIZ_PIXELS_SMALL+75);
    *(ptr_vdma+0x0D) = 200;  // no. FIFO threshhold .. max.. 240

到目前为止我已经做到了,

# vdm memory check
try:
    fd_vdm_path = "/dev/mem"
    mode = "rb+"
    fd_vdm =  open(fd_vdm_path, mode)
    # print(fd_vdm.fileno())
    print("[INFO] " + fd_vdm_path + " checked")

except Exception as error:
    print("{}".format(error))

 # mmap the VDMA device for VDM access
vdma_buf = mmap.mmap(fd_vdm.fileno(), int(VDMA_MAP_SIZE), 
mmap.MAP_SHARED, mmap.PROT_READ|mmap.PROT_WRITE, 0)

ptr_vdm = ctypes.c_uint.from_buffer(vdma_buf)
print(type(ctypes.addressof(ptr_vdm)))
print("[INFO] " + fd_vdm_path + " has allocated virtual address : " + 
hex(ctypes.addressof(ptr_vdm)))

但我一直停留在这里,我不知道如何在python中执行下面的操作。

*(ptr_vdma+5) = FRBUF_ADDR_0;
*(ptr_vdma+7) = 2;  // use internal fifos to trigger xfer
*(ptr_vdma+8) = 20480;
*(ptr_vdma+6) = (75 << 16) + (HORIZ_PIXELS_SMALL+75);
*(ptr_vdma+0x0D) = 200;  // no. FIFO threshhold .. max.. 240

我已经试过了 vdma_buf.write(FRBUF_ADDR_0) 但它不工作,我在网上找不到任何东西(可能是我没有搜索好)

1 回复 | 直到 7 年前

1

3

Igor 7 年前

你可以用 memoryview struct.pack :

...
mm = memoryview(vdma_buf)

mm[5*4:6*4] = struct.pack("I", FRBUF_ADDR_0)
mm[7*4:8*4] = struct.pack("I", 2)
mm[8*4:9*4] = struct.pack("I", 20480)
mm[6*4:7*4] = struct.pack("I", (75 << 16) + (HORIZ_PIXELS_SMALL+75))
mm[0x0D*4:0x0E*4] = struct.pack("I", 200)

.

假设你想在索引处写一个无符号int N . 首先,你打电话 struct.pack("I", ...) 获取int的字节表示。然后必须计算目标内存地址。因为unsigned int的大小是4字节,所以地址等于 N*4个

memoryview支持切片

mm[StartAddress:EndAddress] = BytesYouWantToWrite

其中StartAddress等于N*4,EndAddress为(N+1)*4