我们使用libmodbus库从支持Modbus over RTU的电能表EM6400读取寄存器值。我们正面临以下两个问题。modbus_read_register - 错误连接超时
1)我们所面临的问题与modbus_read_registers
API,这个API返回-1,该错误信息是:
错误连接超时:请选择。
在调试库之后,我们发现这个问题是由于响应消息中请求字节的回显。 read()
_modbus_rtu_recv
中的API调用首先返回请求字节,然后返回响应字节。因此,length_to_read
基于请求字节而不是响应字节(其中包含读取的字节数)在compute_data_length_after_meta()
中计算,并且发生连接超时问题。 我们尝试使用3.0.6和3.1.2 libmodbus版本,但在两个版本中都会出现相同的问题。
2)modbus_rtu_set_serial_mode
(ctx,MODBUS_RTU_RS485)返回“BAD文件描述符”。
请确认是否有任何API调用缺失或任何参数设置不正确。
我们用于读取寄存器值的示例代码如下。这个样本的
int main()
{
modbus_t *ctx;
uint16_t tab_reg[2] = {0,0};
float avgVLL = -1;;
int res = 0;
int rc;
int i;
struct timeval response_timeout;
uint32_t tv_sec = 0;
uint32_t tv_usec = 0;
response_timeout.tv_sec = 5;
response_timeout.tv_usec = 0;
ctx = modbus_new_rtu("/dev/ttyUSB0", 19200, 'E', 8, 1);
if (NULL == ctx)
{
printf("Unable to create libmodbus context\n");
res = 1;
}
else
{
printf("created libmodbus context\n");
modbus_set_debug(ctx, TRUE);
//modbus_set_error_recovery(ctx, MODBUS_ERROR_RECOVERY_LINK |MODBUS_ERROR_RECOVERY_PROTOCOL);
rc = modbus_set_slave(ctx, 1);
printf("modbus_set_slave return: %d\n",rc);
if (rc != 0)
{
printf("modbus_set_slave: %s \n",modbus_strerror(errno));
}
/* Commented - Giving 'Bad File Descriptor' issue
rc = modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
printf("modbus_rtu_set_serial_mode: %d \n",rc);
if (rc != 0)
{
printf("modbus_rtu_set_serial_mode: %s \n",modbus_strerror(errno));
}
*/
// This code is for version 3.0.6
modbus_get_response_timeout(ctx, &response_timeout);
printf("Default response timeout:%ld sec %ld usec \n", response_timeout.tv_sec, response_timeout.tv_usec);
response_timeout.tv_sec = 60;
response_timeout.tv_usec = 0;
modbus_set_response_timeout(ctx, &response_timeout);
modbus_get_response_timeout(ctx, &response_timeout);
printf("Set response timeout:%ld sec %ld usec \n", response_timeout.tv_sec, response_timeout.tv_usec);
/* This code is for version 3.1.2
modbus_get_response_timeout(ctx, &tv_sec, &tv_usec);
printf("Default response timeout:%d sec %d usec \n",tv_sec,tv_usec);
tv_sec = 60;
tv_usec = 0;
modbus_set_response_timeout(ctx, tv_sec,tv_usec);
modbus_get_response_timeout(ctx, &tv_sec, &tv_usec);
printf("Set response timeout:%d sec %d usec \n",tv_sec,tv_usec);
*/
rc = modbus_connect(ctx);
printf("modbus_connect: %d \n",rc);
if (rc == -1) {
printf("Connection failed: %s\n", modbus_strerror(errno));
res = 1;
}
rc = modbus_read_registers(ctx, 3908, 2, tab_reg);
printf("modbus_read_registers: %d \n",rc);
if (rc == -1) {
printf("Read registers failed: %s\n", modbus_strerror(errno));
res = 1;
}
for (i=0; i < 2; i++) {
printf("reg[%d]=%d (0x%X)\n", i, tab_reg[i], tab_reg[i]);
}
avgVLL = modbus_get_float(tab_reg);
printf("Average Line to Line Voltage = %f\n", avgVLL);
modbus_close(ctx);
modbus_free(ctx);
}
}
输出如下:
created libmodbus context
modbus_set_slave return: 0
modbus_rtu_set_serial_mode: -1
modbus_rtu_set_serial_mode: Bad file descriptor
Default response timeout:0 sec 500000 usec
Set response timeout:60 sec 0 usec
Opening /dev/ttyUSB0 at 19200 bauds (E, 8, 1)
modbus_connect: 0
[01][03][0F][44][00][02][87][0A]
Waiting for a confirmation...
ERROR Connection timed out: select
<01><03><0F><44><00><02><87><0A><01><03><04><C4><5F><43><D4><C6><7E>modbus_read_registers: -1
Read registers failed: Connection timed out
reg[0]=0 (0x0)
reg[1]=0 (0x0)
Average Line to Line Voltage = 0.000000
我查看了libmodbus文档,没有读/忽略回显响应的标志。所以,如果OP有一个强制本地回声的RS-485适配器,可能没有太多可以做的事情...... –