Difference between revisions of "Self-driving Car"

Revision as of 20:47, 27 May 2014

This project is about a team of 20 getting a car to self-drive to a selected destination. This involves working with an RTOS running on a low power processor and various different processor boards working together over a CAN bus.

Schedule

<TODO>

Controllers

Given below are the controllers, their duties, and the number of people involved. It is quite possible that one team gets done with their part, but that doesn't mean your job is done. If you are done, help others. If you are done, and the primary objective is met (the car can self-drive), then add more features. There are many things you can do, and the 16-week semester definitely won't provide an opportunity to sit and relax. Get up and learn!.

Sensor Controller (2 members)

• Interfaced to front and rear vision.

  Consider Sonar, and/or IR sensors with long distance vision

• Sensors must be "filtered" and must provide reliable "vision"
• Provide "battery voltage" sense capability

  Better yet, provide percentage of remaining charge of the battery

• What else can you incorporate as additional features?

  Acceleration sensor to provide tilt? (for hill hold assist)

  Light sensor to turn on automatic headlights?

Motor Controller (2 members)

• Interfaced to motor control system of the car

  Provide a means to steer, and drive the car

• Provide feedback of the speed using a wheel encoder or speed sensor

I/O Unit (2 members)

• Provide an LCD screen to report car status

  Errors and communication status

  Sensor values

• Buttons to start and stop the car
• Button hard-coded to set a specific destination
• Provide means to turn on/off the headlights

Communication Bridge + Android (3 members)

• Provide means to communicate and display status on an Android/iPhone device
• Allow a user to see sensor values, car speed (etc)
• Allow a user to select a destination from Google Earth

Geographical Controller (3 members)

• Interface to a 5Hz or faster GPS
• Interface to a backup GPS in case primary one fail (use a different manufacturer)
• Interface to a compass
• Allow a GPS coordinate to be "set"

  Based on the set coordinate, calculate, and provide CAN data regarding

  the current heading, and the desired heading to reach the destination

• This unit needs to compute the "heading degree" to reach the destination

Master Controller(3 members)

• This is the primary unit that communicates with every controller to drive the car
• This unit shall also turn on headlights (etc), and be the "brain" of the car
• Upon a detection of a "Start" condition, work with different controllers to drive the car

  Motor Controller and Geographical Controller

  Command the Motor Controller based on Sensor Controller and Geographical Controller data

Communication

Each controller shall provide a means to communicate with the other controllers. Before you read any further, it requires that you have deep knowledge of the CAN bus. The most important thing to realize is that CAN bus is 1:1 communication rather than 1:many. Although most of the time, all the controllers should only communicate with the Master Controller, sometimes there may be a necessity for any one controller to communicate with a specific controller, therefore we need to provide a means to facilitate this. Given below is an example communication interface for one controller.

Each controller shall pick a controller number. The controller with the highest priority shall pick the lowest ID. Using this protocol, each controller can specifically send a message to any other controller, and likewise, upon a received message, we can tell who it came from.

Recommended CAN Message ID format

Example Controller Communication Table

byte 0: Front sensor value in inches
byte 1: Left sensor value in inches
byte 2: Right sensor value in inches
etc.

Sample Code

/**
 * Have an enumeration of controller IDs
 */
typedef enum {
    cid_geographical_controller = 50,
    cid_master_controller = 60,
} cid_t;

/**
 * Each controller shall then set its own ID
 */
const cid_t our_controller_id = cid_master_controller;

/**
 * Create a "union" whose struct overlaps with the uint32_t
 */
typedef union {
    struct {
        uint32_t id  : 12;  ///< Message ID
        uint32_t src : 8;   ///< Source ID
        uint32_t dst : 8;   ///< Destination ID
        uint32_t : 1;       ///< Unused (29th bit)
    };
    /// This "raw" overlaps with <DST> <SRC> <ID>
    uint32_t raw;

} __attribute__((packed)) controller_id_t;

/**
 * Creates a message ID based on the message ID protocol
 * @param [in] dst  The destination controller ID
 * @param [in] msg_id  The message number to send to the dst controller
 *
 * @returns  The 32-bit message ID created by the input parameters
 */
uint32_t make_id(uint8_t dst, uint16_t msg_id)
{
    controller_id_t cid;
    cid.src = our_controller_id;
    cid.id = msg_id;
    cid.dst = dst;
    return cid.raw;
}



int main(void)
{
    /**
     * We use magic numbers here, but each message ID (such as 0x301) should be
     * part of an enumeration that is shared between different controllers.
     */
    can_msg_t msg = { 0 };
    msg.msg_id = make_id(our_controller_id, cid_geographical_controller, 0x301);

    /**
     * Send the message to the geographical controller to subscribe to
     * GPS data to be sent at 5Hz:
     */
    msg.frame_fields.data_len = 1;
    msg.frame_fields.is_29bit = 1;
    msg.data.bytes[0] = 5;
    CAN_tx(can1, &msg, portMAX_DELAY);

    /**
     * Now, we should be able to retrieve our data from the geographical controller at 5Hz.
     * Since we may have subscribed to many messages, you will need to pCid->src of where
     * the message came from, and then also check the pCid->id to detect what message it is,
     * and then parse the data bytes into our variable types.
     */
    if (CAN_rx(can1, &msg, portMAX_DELAY)) {
        controller_id_t *pCid = &(msg.msg_id);

        /**
         * Check if we got the response from the GPS controller
         * If you subscribe to a lot of messages, you might want to put this 
         * in a large switch statement that calls functions.
         */
        if (pCid->src == cid_geographical_controller)
        {
            if (pCid->id == 0x401) /* 0x401 is a magic num, should be an enum */
            {
                float longitude = * (float*) &(msg.data.bytes[0]);
                float latitude  = * (float*) &(msg.data.bytes[4]);
            }
        }
    }

    return 0;
}

Features

The first feature to develop is the self-drive capability and everything else comes later. While some people in the team may be focusing on delivering this primary feature, other members can focus on other things such as automatic headlights, hill-hold capability etc.

Robustness

Your project is one project as a whole. So if it doesn't work, do not blame it on "hey, their controller crashed". If a controller crashes it will restart, and the subscribed messages will vanish. If subscribed messages vanish, other controllers should re-subscribe. So your code should be robust, and self-recover from any crashed event or any brief power disruptions.

Likewise, if you send a message, and it fails (in case the other controller is down), your CAN bus may go to abnormal state and turn off. In this condition, all of your messages will fail, and the entire communication needs to be re-done including all the subscriptions. I recommend the following:

• Attach a BUS off callback function that gives "can_bus_crashed" semaphore.
• If the semaphore is ever given, reset your CAN bus, and re-subscribe to the desired messages.

Considerations

You should consider and design your software for all of these events:

• Where is the kill switch?
• Can you remotely shut down the car in 3 seconds?
• Where is the kill switch?
• If controller A sends subscription message twice, are you sure you won't double subscribe?
• If your controller goes down, will it fully recover to "last known configuration"?
• If you stop receiving subscribed messages, what will you do?
• If critical sensor data stops coming, how will you stop the car?
• How can you quickly discover one or more controllers reaching an error state?
• Log the data on the SD card as much as possible.
• If something wrong happens, you need to know what happened.

Grade

Your grade is relative. The best team earns the best grade. Remember than three out of three features working 100% is far better than nine out of ten features working. Focus on less features, with highest quality.