Difference between revisions of "CAN Communication"

Revision as of 13:46, 2 July 2019

CAN Communication Tutorial

Please download CAN_tutorial.zip file and follow below steps. File:CAN tutorial.zip
CAN_tutorial.zip contains CMakeList.txt, README and grasp directory.

This tutorial will show how to open & close CAN communication. Also, how to get position data and send pwm to operate Allegro Hand. You will follow step by step with adding sample codes. Source code assumes you have a peak-systems pcan to usb adapter so if you are not using PEAK CAN device, please check your own device CAN api and channel.

simple diagram

Below picture shows a structure of a sample program for this tutorial.

main.cpp

You can find main.cpp in grasp directory. There are 3 functions you have to edit.

Initialize CAN I/O thread and start.

// Open a CAN data channel
bool OpenCAN()
{
    printf(">CAN(%d): open\n", CAN_Ch);
 
    // CAN open
    int ret = command_can_open(CAN_Ch);
    if(ret < 0)
    {
        printf("ERROR command_can_open !!! \n");
        return false;
    }
 
    // initialize CAN I/O thread
    ioThreadRun = true;
    pthread_create(&hThread, NULL, ioThreadProc, 0);
    printf(">CAN: starts listening CAN frames\n");
 
    // set periodic communication parameters(period)
    printf(">CAN: Comm period set\n");
    short comm_period[3] = {3, 0, 0}; // millisecond {position, imu, temperature}
    ret = command_set_period(CAN_Ch, comm_period);
    if(ret < 0)
    {
        printf("ERROR command_set_period !!! \n");
        command_can_close(CAN_Ch);
        return false;
    }
 
    // servo on
    printf(">CAN: servo on\n");
    ret = command_servo_on(CAN_Ch);
    if(ret < 0)
    {
        printf("ERROR command_servo_on !!! \n");
        command_set_period(CAN_Ch, 0);
        command_can_close(CAN_Ch);
        return false;
    }
 
    return true;
}

Get CAN raw data and identify data to get position values.

// CAN communication thread
static void* ioThreadProc(void* inst)
{
    int id;
    int len;
    unsigned char data[8];
    unsigned char data_return = 0;
    int i;
 
    while (ioThreadRun)
    {
        /* wait for the event */
        while (0 == get_message(CAN_Ch, &id, &len, data, FALSE))
        {
            switch (id)
            {
            case ID_RTR_FINGER_POSE_1:
            case ID_RTR_FINGER_POSE_2:
            case ID_RTR_FINGER_POSE_3:
            case ID_RTR_FINGER_POSE_4:
            {
                int findex = (id & 0x00000007);
                vars.enc_actual[findex*4 + 0] = (short)(data[0] | (data[1] << 8));
                vars.enc_actual[findex*4 + 1] = (short)(data[2] | (data[3] << 8));
                vars.enc_actual[findex*4 + 2] = (short)(data[4] | (data[5] << 8));
                vars.enc_actual[findex*4 + 3] = (short)(data[6] | (data[7] << 8));
 
                // convert encoder count to joint angle
                for (i=0; i<MAX_DOF; i++)
                {
                    q[i] = (double)(vars.enc_actual[i])*(333.3/65536.0)*DEG2RAD;
                }
 
                // print joint angles
                for (int i=0; i<4; i++)
                {
                    printf(">CAN(%d): Joint[%d] Pos : %5.1f %5.1f %5.1f %5.1f\n"
                        , CAN_Ch, i, q[i*4+0]*RAD2DEG, q[i*4+1]*RAD2DEG, q[i*4+2]*RAD2DEG, q[i*4+3]*RAD2DEG);
                }
                break;
            }
 
            default:
                printf(">CAN(%d): unknown command %d, len %d\n", CAN_Ch, id, len);
            }
        }
    }
    return NULL;
}

CloseCAN()

// Close CAN data channel
void CloseCAN()
{
    printf(">CAN: stop periodic communication\n");
 
    //close CAN listening thread
    if (ioThreadRun)
    {
        printf(">CAN: stoped listening CAN frames\n");
        ioThreadRun = false;
        int status;
        pthread_join(hThread, (void **)&status);
        hThread = 0;
    }
 
    // CAN close
    printf(">CAN(%d): close\n", CAN_Ch);
    int ret = command_can_close(CAN_Ch);
    if(ret < 0) printf("ERROR command_can_close !!! \n");
}

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@@ Line 15: / Line 15: @@
 <br><br>
-OpenCAN() function initialize CAN I/O thread and start it.
+Initialize CAN I/O thread and start.
 <syntaxhighlight lang="cpp">
 // Open a CAN data channel
@@ Line 62: / Line 62: @@
 <br><br>
+Get CAN raw data and identify data to get position values.
-ioThreadProc(void* inst)
 <syntaxhighlight lang="cpp">
 // CAN communication thread