Difference between revisions of "Communication"
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==Elcano CAN Commands==
==Elcano CAN Commands==
Latest revision as of 19:43, 12 July 2019
- 1 Elcano CAN Commands
Elcano CAN Commands
Controller Area Network (CAN) is a standard introduced by Bosch in the 1980s. It is widely used to link automotive microprocessors and is required on all cars sold in North America and Europe. Physically there are four wires: Ground, 12V, CanHi and CanLo. A dominant bit has a significant difference between CanHi and CanLo; for a recessive bit the two lines are essentially the same. The interesting parts of a CAN packet are given in the table. The message ID is 11 bits, with low numbers getting priority. A CAN packet contains 0 to 8 bytes of data. The size of a CAN packet is larger, since CAN has significant error detection capability. CAN is a host-less network with most of the work done in hardware.
|CAN ID||Origin||Byte 1||Byte 2||Byte 3||Byte 4||Byte 5||Byte 6||Byte 7||Byte 8||Function|
|0x350||Hi-Level||xx||xx||Drive Speed cm/s|
|0x350||Hi-Level||xx||xx||Drive angle (10 times degrees)|
|0x400||Lo-Level||xx||xx||Actual Speed cm/s|
|0x400||Lo-Level||xx||xx||Actual angle (10 times degrees)|
|0x4A0||Camera||xx||xx||yy||yy||zz||zz||Right road edge|
|0x4A1||Camera||xx||xx||yy||yy||zz||zz||Left road edge|
|0x4C1||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 1 Position|
|0x4C2||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 2 Position|
|0x4C3||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 3 Position|
|0x4C4||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 4 Position|
|0x4C5||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 5 Position|
|0x4C6||?||xx||xx||xx||xx||yy||yy||yy||yy||Goal 6 Position|
** Please be aware of the initial CAN-Bus baud rate. If you use MCP2515 module for testing, the baud rate needs to be set to twice the due CAN baud rate
Not all commands will be implemented. All data are given in integer; floating point is not used.
Command 0x50, 0x100, and 0x200 (status change)
use Byte 1.
If bit 0x80 is set, emergency stop is active.
Bit 0x40 when set puts the trike in autonomous mode; reset puts it in manual mode.
If bit 0x04 is zero, the trike is going forward. When the receiver (0x50) sets bit 0x04, it is requesting reverse. Low Level responds with a 0x200 message with bit 0x04 set meaning that reverse is active, bit 0x02 set meaning that reverse is pending or bit 0x01 set meaning that reverse is not available.
The Receiver would output a 0x50 message only when the status changes. It expects to receive a 0x200 message for e-stop active shortly afterwards (maybe 100 ms), and will resend 0x50 until it receives a 0x200.
Goal Reached (CANID 0x101)
If 0x80 is set, all goals have been reached and the vehicle should stop.
Bit 0x01: goal one has been reached and goal two is next.
Bits 0x02, 0x04, 0x08, 0x10, 0x20: Reached goals 2, 3, 4, 5, and 6 respectively.
gives the relative amount to go, stop or turn. For each, 12 bits will suffice, and fewer bytes than indicated could be used. These are uncalibrated relative amounts from minimum to maximum. At present, positive values are throttle and negative values are brake, and it is impossible to accelerate of brake at the same time. In the future, we may want to allow both simultaneously. At present brakes are either on or off; we may use intermediate values to pulse the brakes. A negative steering value indicates left; positive value indicates right; 0 is straight.
DRIVE (CANID 0x350)
0x350 ComandedSpeed, Brake, ComandedSteerAngle
ID350 gives the command drive speed, brake and angle.
This utilizes 6 of the 8 data bytes
ComandedSpeed is a 16-bit signed integer giving the speed for the rear wheel in centimeters per second. It occupies data bytes 1 and 2. The value is the speed, in centimeters / second. Maximum value is 0x7FFF = 32767 cm/s = 730 mph.
Brake is a 16-bit signed integer giving signal to brake. Currently brake is only on or off, but could have pulses added later to be different levels of braking.
ComandedSteerAngle is a16-bit signed integer that specifies the steer angle (in degrees times 10) of the vehicle. Negative value indicates left; positive value indicates right; 0 is straight. It occupies data bytes 5 and 6. Maximum value is 1800; Minimum value is -1800. The trikes are not capable of turning more than ±30°, but other vehicles could be holomorphic.
e.g. commanding 1.5 m/s with a 2.1° left turn gives
|120||05 DC||FF EB||hex|
ACTUAL (CANID 0x400)
0x400 ActualSpeed, ActualAngle
ID400 gives the reports the actual speed and angle from the low-level board to the high-level.
This utilizes 4 of the 8 data bytes
ActualSpeed is a 16-bit signed integer giving the speed for the rear wheel in centimeters per second. It occupies data bytes 1 and 2, formatted identically to ComandedSpeed in DRIVE(0x350) above.
ActualAngle is a16-bit signed integer that specifies the steer angle (in degrees times 10) of the vehicle. It occupies data bytes 5 and 6, formatted identically to ComandedSteerAngle in DRIVE(0x350) above.
Obstacle Data (0x420, 0x440, 0x460)
Uses 6 or 8 bytes
Bytes 1,2: Range to obstacle centroid in cm.
Bytes 3,4: Bearing to obstacle centroid in degrees times 10. Negative is left; positive is right.
Byte 5: Obstacle half-width in degrees times 10. If bearing is b and half-width is w, obstacle extends from b-w to b+w. For sensors with limited resolution, byte 5 gives the resolution. For example, a sonar that covers 30 degrees would set byte 5 to 150.
Byte 6: Quality of the signal/data. 0 = no data; 255 = highest quality
Bytes 7,8: Obstacle slant in degrees times 10 (optional). If omitted or 0, the obstacle is perpendicular to the bearing. Otherwise a negative angle indicates that the left side of the obstacle is closer, and a positive angle means the left side is farther than the centroid.
Cone Position (0x480)
Position of the next cone, using 6 bytes in the same format as obstacle data.
Byte 5 is the half-width of the cone at the base.
Road Edge (0x4A0, 0x4A1)
Estimated distance from vehicle edge to road edge in cm based on present trajectory.
Bytes 1,2: At present vehicle position
Bytes 3,4: At a near future position (to be defined)
Bytes 5,6: At a farther future position (to be defined)
Goal Positions (0x4C1 … 0x4C6)
Positions of cones or other goals. Not defined how this would be input; perhaps from a user interface. They can be hard coded for now.
Bytes 1-4: East position in cm
Bytes 5-8 North position in cm.