我的设置是这样的:一台旧的Windows XP计算机仍然具有真实的串行端口,而一台更新的Windows 7计算机使用USB串行适配器。我正在尝试运行如下所示的librs232示例:
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include "librs232/rs232.h"
unsigned int err(unsigned int e);
unsigned int rs232_simple_test(void);
unsigned int err(unsigned int e)
{
printf("%s (%s)\n", rs232_strerror(e), errno > 0 ? strerror(errno) : "");
return e;
}
unsigned int rs232_simple_test(void)
{
unsigned int try = 0;
unsigned int bytes = 0;
unsigned char data[1];
unsigned int ret = 0;
struct rs232_port_t *p = NULL;
p = rs232_init();
if (p == NULL)
return 1;
#ifdef WIN32
rs232_set_device(p, "COM1");
#else
rs232_set_device(p, "/dev/ttyUSB0");
#endif
ret = rs232_open(p);
if (ret) {
rs232_end(p);
return err(ret);
}
rs232_set_baud(p, RS232_BAUD_9600);
printf("[*] port settings: %s\n", rs232_to_string(p));
rs232_flush(p);
while (try++ < 10) {
printf("%02d. [*] read: ", try);
data[0] = 0x00;
ret = rs232_read_timeout(p, data, 1, &bytes, 1000);
if (ret)
err(ret);
else
printf("0x%02x len: %d\n", data[0], bytes);
data[0] = 0x05;
bytes = 0;
printf("%02d. [*] write: ", try);
ret = rs232_write_timeout(p, data, 1, &bytes, 1000);
if (ret)
err(ret);
else
printf("len: %d\n", bytes);
}
rs232_end(p);
return 0;
}
int main()
{
return rs232_simple_test();
}
此代码连续十次向COM1发送字符0x05。我在Win7机器上运行测试程序。但是,WinXP计算机上的输出是这样的:
0x05
0x05
0x05
0x05
0x05
0x05
0x05
0x05
0x05
0x0500fc
您可以看到在最后一次串行写入操作中,突然多了两个字节(0x00fc)。这是为什么?那两个人从哪里来?我不明白同样,上面显示的测试程序的输出清楚地表明仅发送了1个字节:
[*] port settings: device: COM1, baud: 9600, data bits: 8, parity: none, stop bits: 1, flow control: off
01. [*] read: timeout error (No such file or directory)
01. [*] write: len: 1
02. [*] read: timeout error (No such file or directory)
02. [*] write: len: 1
03. [*] read: timeout error (No such file or directory)
03. [*] write: len: 1
04. [*] read: timeout error (No such file or directory)
04. [*] write: len: 1
05. [*] read: timeout error (No such file or directory)
05. [*] write: len: 1
06. [*] read: timeout error (No such file or directory)
06. [*] write: len: 1
07. [*] read: timeout error (No such file or directory)
07. [*] write: len: 1
08. [*] read: timeout error (No such file or directory)
08. [*] write: len: 1
09. [*] read: timeout error (No such file or directory)
09. [*] write: len: 1
10. [*] read: timeout error (No such file or directory)
10. [*] write: len: 1
那么为什么在最后一次写入操作中3个字节到达WinXP PC?
我检查了两台机器上的波特率,数据位,奇偶校验,流控制和停止位设置是否相同,并且它们也与上述代码中设置的波特率(9600波特)匹配,所以我真的不知道那里怎么了这里的任何人都可以告诉更多信息吗?