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The xArm has three means of communication.
- HID-USB
- TTL serial 9600 BAUD
- Game Controller which appearently does not function even though the controller and adapter are provided.
Uses https://github.com/mikeobrien/HidLibrary.
In general terms, a packet transmitted to the xArm will have the following format.
| id | header | length | command | parameters | |
|---|---|---|---|---|---|
| Bytes | 1 | 2 | 1 | 1 | 0 or more |
| Comments | Any number. | Always 0x5555. | Here to end. | See commands. | See commands. |
Commands are essentially request packets embedded into USB HID reports.
USB HID reports generally have output and input data block lengths of 64 bytes. A USB HID report prepends an id byte so that messages spanning more than one block may be identified by their sequential block id. How how this is implemented is application specific. For purposes of controlling the xArm, a message never exceeds the maximum report length.
Requests and Reqponses are described in the following syntax:
- Each field is seperated by a space.
- Each field is described by the type in parentheses.
- Curly braces denote that their content may be repeated more than once.
Read the offset value of one or more servos.
Request: (byte)count { (byte)id }
Response: (byte)count { (byte)id (sbyte)offset }
Parameters: count is the number of servos in id list. id is one or more servo ids. offset is a signed byte with valid range of -128 to 128.
ServoMove 3 (byte)count (ushort)time { (byte)id (ushort)position }
GroupRunRepeat 5 (byte)group[255=all] (byte)times
GroupRun 6 (byte)group (ushort)count[0=continuous]
GroupStop 7 -none-
GroupErase 8 (byte)group[255=all]
GroupSpeed 11 (byte)group (ushort)percentage
xServoOffsetWrite 12 *** not sure
xServoOffsetRead 13 *** not sure
xServoOffsetAdjust 14 *** not sure
GetBatteryVoltage 15 -none-; (ushort)millivolts
ServoOff 20 (byte)count { (byte)id }
ServoPositionRead 21 (byte)count { (byte)id }; (byte)count { (byte)id (ushort)position }
ServoPositionWrite 22 (byte)count { (byte)id (ushort)position }
ServoOffsetRead 23 (byte)count { (byte)id }; (byte)count { (byte)id (sbyte)offset }
ServoOffsetWrite 24 (byte)id (sbyte)offset
BusServoMoroCtrl 26 (byte)id (byte)??? (ushort)speed
**These commands will affect all attached servos. Use these commands with only one servi attached.**
BusServoInfoWrite 27 (byte)id (ushort)pos_min (ushort)pos_max (ushort)volt_min
(ushort)volt_max (ushort)temp_max (byte)led_status
(byte)led_warning
BusServoInfoRead 28 -none-; (byte)id (ushort)pos_min (ushort)pos_max (ushort)volt_min
(ushort)volt_max (ushort)temp_max (byte)led_status
(byte)led_warning (byte)dev_offset (ushort)pos (byte)temp
(ushort)volt
BusServoInfoWrite affects all servos attached. Each servo must be programmed individually with the BusServoInfoWrite command. Reading info from the servos must also be performed individually.
Temperature range 50C to 100C in 1C increments. Default is 85C. The 16-bit field value is expressed in Centigrade.
Voltage range 4.5V to 12V in 0.1V increments. Default is 4.5V(min) and 12V(max). The 16-bit field value is expressed in millivolts, 4500mV(min) and 12000mV(max).
I have not tested it but I believe the ServoOff command will toggle the servo on and off and any servo movement command will turn it on if it was off.
List<DispatcherTimer> dispatchTimers is declared as a private property in MainWindow.cs only for possible future reference and is not used anywhere else.
InitializeDispatcherTimers() is declared in MainWindow() and initializes 16-millisecond and 300-millisecond timers.
The DispatcherTimer will append up to one Tick to the Interval specified if that period exceeds one Tick's period. A Tick seems to be about slightly faster than 1/60th of a second. Put another way, the Tick event will fire when the master Tick has occured, even if the specified period has been exceeded.
This timer is the game loop for the application and has a nominal frequency of 60Hz. It has two functions:
- Perform scope's UI updates.
- Manage communication timing.