Serial Communication

The information on this page refers to firmware v2.69a and higher.

Communication with the STorM32 board is possible through the serial interfaces USB, UART, and UART2 (Bluetooth and Wifi can be achieved by using corresponding dongles). Three sets of commands are available for serial communication:

• Simple Commands: This set has a very simple command structure, and is used for major tasks of the GUI.
• RC Commands: This set is targeted at a remote control of the STorM32 gimbal.
• Mavlink Commands: This set is "real" MAVLink.

The simple and the RC commands share many similarities, and could be considered the two sides of a coin (they both are in fact processed by the same code part in the firmware). They tend to be more efficient than the MAVLink commands. Any command of any set can be processed through any of the serial interfaces. However, when the MAVLink Gimbal or MAVLink Camera component is activated, then the serial port selected for MAVLink accepts only MAVLink commands, and on v1.3x boards also Bluetooth may not be used anymore.

The commands of each of the three command sets can be used interchangeably. The command set whih the command belongs to is determined by the first received character. This implies that in case of a communication error, the message parser may misinterpret characters which follow the error. The message parser is reset after a timeout.

For understanding all details of the communication, it is generally best to peek into the source code of the GUI (which is included in any firmware package). It's written in Perl, and Perl is sufficiently primitive to understand the code easily.

Serial Communication - Simple Commands

This protocol for the communication via the serial interfaces follows these rules:

• The board responds to incoming commands by sending back a data stream of one or more characters, which is determined by the received command.
• The board is never sending/transmitting anything by itself, that is, a transmission is always started only as a reaction to an incoming command.
• The board is responding to any incoming command, be it valid or not.

Any data packet returned by the board ends with one of these characters:

• 'o': indicates that everything is ok, i.e. that the received command has been identified
• 'e': indicates that an error has occurred, i.e. that an invalid command has been received
• 't': indicates that a timeout has occurred, i.e. that a command which consists of several characters was not completed within a certain time window
• 'c': indicates that a checksum error has occurred

A checksum is invoked whenever data are transmitted, as e.g. for the 'p','g', and 'd' commands.

Comment: Only the most important simple commands are listed below. There are many more for interacting with the GUI; please inspect the GUI source code to identify them and their usage.

Command 't'

This command simply returns the character 'o'. Can be used by the host to check if the board is still connected.

Command 'v'

This command returns information on the installed firmware version, the name of the board, and the type of the board. The data packet is appended by a crc, and closed with the character 'o'.

Command 'g'

This command returns a data packet containing all parameter values. The data packet is appended by a crc, and closed with the character 'o'.

Command 'p'

This command sets all parameter values. The command character 'p' needs to be followed by a data packet containing all parameter values, plus a crc. It returns the character 'o'.

Command 'd'

Upon receipt of the command 'd' a data packet containing the current live data is transmitted. The live data is appended by a crc, and closed with the character 'o'. The respective C code snippet is as follows:

 //send 32 data values
 uart_prepare_transmit();
 ((u16*)buf)[pos++] = STATE; //state
 ((u16*)buf)[pos++] = status; //status
 ((u16*)buf)[pos++] = status2; //status2
 ((u16*)buf)[pos++] = status3; //status3
 ((u16*)buf)[pos++] = (s16)(Performance.MaxLoopdone*10); //performance
 ((u16*)buf)[pos++] = imu_ntbus_geterrocnt() + imu_onboard_geterrocnt(); //errors
 ((u16*)buf)[pos++] = lipo_voltage(); //lipo_voltage;
 ((u16*)buf)[pos++] = (u16)looptime.millis_32; //timestamp
 ((u16*)buf)[pos++] = (u16)(1.0E6f*FDT); //cycle time
 ((u16*)buf)[pos++] = (s16)(100*aImu1Angle.Pitch); //Imu1 angles, in 0.01°
 ((u16*)buf)[pos++] = (s16)(100*aImu1Angle.Roll);
 ((u16*)buf)[pos++] = (s16)(100*aImu1Angle.Yaw);
 ((u16*)buf)[pos++] = (s16)(10000*Imu1AHRS.R.x); //Imu1 R estimates, in 0.0001 g
 ((u16*)buf)[pos++] = (s16)(10000*Imu1AHRS.R.y);
 ((u16*)buf)[pos++] = (s16)(10000*Imu1AHRS.R.z);
 if( IS_ENCODERS_ENABLED ){
   ((u16*)buf)[pos++] = (s16)(100*cPID[PITCH].Cntrl); //PID output, in 0.01°
   ((u16*)buf)[pos++] = (s16)(100*cPID[ROLL].Cntrl);
   ((u16*)buf)[pos++] = (s16)(100*cPID[YAW].Cntrl);
 }else{
   ((u16*)buf)[pos++] = (s16)(100*cPID[PITCH].Cntrl - aImu1Angle.Pitch); //relative PID output, in 0.01°
   ((u16*)buf)[pos++] = (s16)(100*cPID[ROLL].Cntrl - aImu1Angle.Roll);
   ((u16*)buf)[pos++] = (s16)(100*cPID[YAW].Cntrl - aImu1Angle.Yaw);
 }
 ((u16*)buf)[pos++] = InputSrc.Pitch; //Rc Input values
 ((u16*)buf)[pos++] = InputSrc.Roll;
 ((u16*)buf)[pos++] = InputSrc.Yaw;
 ((u16*)buf)[pos++] = (s16)(100*aImu2Angle.Pitch); //Imu2 angles, in 0.01°
 ((u16*)buf)[pos++] = (s16)(100*aImu2Angle.Roll);
 ((u16*)buf)[pos++] = (s16)(100*aImu2Angle.Yaw);
 if( IS_ENCODERS_ENABLED ){
   ((u16*)buf)[pos++] = (s16)(100*motorfoc_aEncoderAngle(PITCH)); //Encoder angles, in 0.01°
   ((u16*)buf)[pos++] = (s16)(100*motorfoc_aEncoderAngle(ROLL));
   ((u16*)buf)[pos++] = (s16)(100*motorfoc_aEncoderAngle(YAW));
 }else{
   ((u16*)buf)[pos++] = (s16)(100*cPID[PITCH].MotorCntrl); //Motor angles, in 0.01°
   ((u16*)buf)[pos++] = (s16)(100*cPID[ROLL].MotorCntrl);
   ((u16*)buf)[pos++] = (s16)(100*cPID[YAW].MotorCntrl);
 }
 ((u16*)buf)[pos++] = (s16)(0.0f);
 ((u16*)buf)[pos++] = (s16)(0.0f); //link yaw
 ((u16*)buf)[pos++] = (s16)(10000*Imu1AHRS._acc_magnitude);
 ((u16*)buf)[pos++] = (s16)(10000*Imu1AHRS._acc_confidence);
 ((u16*)buf)[pos++] = pack_functioninputvalues(&FunctionInputPulse);  //Function input values
 (*len)*=2;
 //add crc
 uint16_t crc= do_crc( fbuf, fbuf_len );
 fbuf[fbuf_len++]= (u8)crc; //low byte
 fbuf[fbuf_len++]= (u8)(crc>>8); //high byte
 //end character
 uart_transmit_ackchar( closewith ); //this sends a 'o'

Command 's'

Upon receipt of the command 's' a data packet containing the current status data is transmitted. The data packet is appended by a crc, and closed with the character 'o'. The command is essentially identical to the 'd' command, except that it transmits only the first seven data values.

Checksum

The checksum for protecting some data packets is the x25 16-bit crc used by MAVLink. C code can be found here.

Serial Communication - RC Commands

In addition to the simple serial commands described in the previous section, the STorM32 controller also understands some messages targeted at remote control of the gimbal. These messages have a stricter data format, and provide a higher level of transmission reliability. They also provide a much richer command set and allow access to STorM32's full potential.

The rules of the communication are exactly as before:

• The STorM32 board emits a message only upon request, but never by itself.
• Any received message is acknowledged by a message send back to the host.

The general structure of a data frame is:

* Startsign: 0xFA for incoming messages, and 0xFB for outgoing messages
* Length: length of the payload, i.e. number of bytes of the data packet excluding
           Start sign, Length byte, Command byte, and crc word
* Command: the command byte
* Payload: as many bytes as expected by the command
* Checksum: x25 16-bit crc excluding start byte, as used by MAVLink; C code can be found here

Comment: The response can be suppressed by using a 0xF9 start sign, instead of a 0xFA.

The following commands can be send to the STorM32 controller:

CMD_GETVERSION (#1)

0xFA 0x00 0x01 crc-low-byte crc-high-byte

If an error occurred a CMD_ACK message will be emitted. Otherwise a message containing the firmware version, the setup layout version and board capabilities in this format will be emitted:

0xFB 0x06 0x01 data1-low data1-high data2-low data2-high data3-low data3-high crc-low-byte crc-high-byte

Data1 is the firmware version, data2 the setup layout version, and data3 holds the board capabilities value.

CMD_GETVERSIONSTR (#2)

0xFA 0x00 0x02 crc-low-byte crc-high-byte

If an error occurred a CMD_ACK message will be emitted. Otherwise a message containing the version string, name string and board string in this format will be emitted:

0xFB 0x30 0x02 data-stream crc-low-byte crc-high-byte

The data stream contains the 16 bytes version string, the 16 bytes name string and the 16 bytes board string.

CMD_GETPARAMETER (#3)

0xFA 0x02 0x03 data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and represents the number of the parameter which is requested. If an error occurred a CMD_ACK message will be emitted. Otherwise a message containing the parameter value in this format will be emitted:

0xFB 0x04 0x03 data1-low-byte data1-high-byte data2-low-byte data2-high-byte crc-low-byte crc-high-byte

Data1 is the parameter number and data2 holds the parameter value.

CMD_SETPARAMETER (#4)

0xFA 0x04 0x04 data1-low-byte data1-high-byte data2-low-byte data2-high-byte crc-low-byte crc-high-byte

Data1 is the parameter number and data2 holds the parameter value. As response to this command a CMD_ACK message will be emitted.

CMD_GETDATA (#5)

0xFA 0x01 0x05 type-byte crc-low-byte crc-high-byte

Type specifies the type of the requested data stream; currently only type 0 is supported. If an error occurred a CMD_ACK message will be emitted. Otherwise a message containing the data stream in this format will be emitted:

0xFB 0x4A 0x05 type-byte 0x00 data-stream crc-low-byte crc-high-byte

The data stream contains the same data as send by the 'd' command.

CMD_GETDATAFIELDS (#6)

0xFA 0x02 0x06 data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and represents a bitmask to specify which data should be send. If an error occurred a CMD_ACK message will be emitted. Otherwise a message containing the bitmask word and all the requested data in this format will be emitted:

0xFB LEN 0x06 data1-low-byte data1-high-byte data-stream crc-low-byte crc-high-byte

Data1 is the bitmask word, and data-stream holds the data. The following bits can be raised:

0x0002 = LIVEDATA_TIMES
0x0004 = LIVEDATA_IMU1GYRO
0x0008 = LIVEDATA_IMU1ACC
0x0010 = LIVEDATA_IMU1R
0x0020 = LIVEDATA_IMU1ANGLES
0x0040 = LIVEDATA_PIDCNTRL
0x0080 = LIVEDATA_INPUTS
0x0100 = LIVEDATA_IMU2ANGLES
0x0400 = LIVEDATA_STORM32LINK
0x0800 = LIVEDATA_IMUACCSTATS
0x1000 = LIVEDATA_ATTITUDE_RELATIVE
0x2000 = LIVEDATA_STATUS_V2
0x4000 = LIVEDATA_ENCODERANGLES

Comment: These flags have slightly changed in v2.61, so are slightly different in older firmware versions.

CMD_SETPITCH (#10)

0xFA 0x02 0x0A data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and can assume the values 700...2300. It represents the pitch input value. If the value 0 is send, then the pitch axis will be recentered. Any other values are ignored. As response to this command a CMD_ACK message will be emitted.

CMD_SETROLL (#11)

0xFA 0x02 0x0B data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and can assume the values 700...2300. It represents the roll input value. If the value 0 is send, then the roll axis will be recentered. Any other values are ignored. As response to this command a CMD_ACK message will be emitted.

CMD_SETYAW (#12)

0xFA 0x02 0x0C data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and can assume the values 700...2300. It represents the yaw input value. If the value 0 is send, then the yaw axis will be recentered. Any other values are ignored. As response to this command a CMD_ACK message will be emitted.

CMD_SETPANMODE (#13)

0xFA 0x01 0x0D data-byte crc-low-byte crc-high-byte

The data is of type uint8_t and can assume these values: 0 = off, 1 = HOLDHOLDPAN, 2 = HOLDHOLDHOLD, 3 = PANPANPAN, 4 = PANHOLDHOLD, 5 = PANHOLDPAN, 6 = HOLDPANPAN. As response to this command a CMD_ACK message will be emitted.

CMD_SETSTANDBY(#14)

0xFA 0x01 0x0E data-byte crc-low-byte crc-high-byte

The data is of type uint8_t and can assume these values: 0 = off, 1 = on. As response to this command a CMD_ACK message will be emitted.

CMD_DOCAMERA(#15)

0xFA 0x06 0x0F dummy-byte data-byte dummy-byte dummy-byte dummy-byte dummy-byte crc-low-byte crc-high-byte

The data is of type uint8_t and can assume these values: 0 = off, 1 = SHUTTER, 2 = SHUTTERDELAYED, 3 = VIDEOON, 4 = VIDEOOFF. As response to this command a CMD_ACK message will be emitted.

CMD_SETSCRIPTCONTROL (#16)

0xFA 0x02 0x10 data1-byte data2-byte crc-low-byte crc-high-byte

The data1 and data2 are of type uint8_t. Data1 is the number of the script (0 = scritp1, 1 = script2, etc) and data2 can assume these values: 0 = off, 1 = CASE#DEFAULT, 2 = CASE#1, 3 = CASE#2, 4 = CASE#3, 5 = CASE#4. As response to this command a CMD_ACK message will be emitted.

CMD_SETANGLES (#17)

0xFA 0x0E 0x11 float1 float2 float3 flags-byte type-byte crc-low-byte crc-high-byte

The float1, float2, float3 fields represent 4 bytes each. They are of type float, and correspond to the pitch, roll, and yaw angles in degree. The flags and type bytes are not used and have to be set to zero. As response to this command a CMD_ACK message will be emitted. Comment: In previous firmware versions the flags byte allowed to set the behavior of the angle setting for each axis to unlimited or limited mode. The behavior now corresponds to flags 0, or unlimited mode for all axes.

CMD_SETPITCHROLLYAW (#18)

0xFA 0x06 0x12 data1-low-byte data1-high-byte data2-low-byte data2-high-byte data3-low-byte data3-high-byte crc-low-byte crc-high-byte

The data1, data2 and data3 are each of type uint16_t and can assume the values 700...2300. They represent the pitch, roll, yaw input values. If a value 0 is send, then the respective axis will be recentered. Any other values are ignored. As response to this command a CMD_ACK message will be emitted.

CMD_SETPWMOUT (#19)

0xFA 0x02 0x13 data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and can assume the values 700...2300. It represents the pwm pass through input value. As response to this command a CMD_ACK message will be emitted.

CMD_RESTOREPARAMETER (#20)

0xFA 0x02 0x14 data-low-byte data-high-byte crc-low-byte crc-high-byte

The data is of type uint16_t and holds the parameter number. This command sets the parameter to the value in the EEPROM. As response to this command a CMD_ACK message will be emitted.

CMD_RESTOREALLPARAMETER (#21)

0xFA 0x00 0x15 crc-low-byte crc-high-byte

This command sets all parameters to the values stored in the EEPROM. As response to this command a CMD_ACK message will be emitted.

CMD_SETINPUTS (#22)

0xFA 0x17 0x16 data-bytes crc-low-byte crc-high-byte

This overwrites the data received from virtual inputs, if Virtual Channel Configuration = “serial” is configured. The data bytes are formatted similarly to sbus: 16 channels of 11 bit values combined into 22 bytes, plus a status byte. The range is 0...2047, and 1500 equals center. As response to this command a CMD_ACK message will be emitted.

CMD_SETHOMELOCATION (#23)

Deprecated.

CMD_SETTARGETLOCATION (#24)

Deprecated.

CMD_SETINPUTCHANNEL (#25)

0xFA 0x04 0x19 data1-low data1-high data2-low data2-high crc-low-byte crc-high-byte

This overwrites the data received from virtual inputs for the specified channel, if Virtual Channel Configuration = “serial” is configured. The data1 and data2 are of type uint16_t each. Data1 is the channel number. Data2 is the channel value, the range is 700...2300, and 1500 equals center. As response to this command a CMD_ACK message will be emitted.

CMD_SETCAMERA (#26)

0xFA 0x04 0x1A data1-low data1-high data2-low data2-high crc-low-byte crc-high-byte

The data1 and data2 are of type uint16_t each, and can assume the values 700...2300, and 1500 equals center. If the value 0 is send, then the respective input is cleared. Any other values are ignored. Data1 and data2 represent the camera control and camera control2 input values, respectively. As response to this command a CMD_ACK message will be emitted.

CMD_SENDCAMERACOMMAND (#27)

0xFA 0x01-0x12 0x1B data1 ... data24 crc-low-byte crc-high-byte

The data1 to data18 are of type uint8_t. The message can have 1 to 24 of them, i.e., length byte can vary from 0x01 to 0x12. The data are send to the NT Camera uart port. As response to this command a CMD_ACK message will be emitted.

CMD_SETANGLES_UNRESTRICTED (#28)

0xFA 0x18 0x1C float1 float2 float3 float4 float5 float6 crc-low-byte crc-high-byte

The float1 - float6 fields represent 4 bytes each. They are of type float. Float1, float2, float3 correspond to the desired pitch, roll, and yaw angles in degrees. Float4, float5, float6 correspond to the desired pitch rate, roll rate, and yaw rate in degrees per second (only positive values are admitted). A value of zero means that no rate is applied. Comment: The rates are not the components of the angular velocity vector, but indeed the rates of the respective angles. As response to this command a CMD_ACK message will be emitted.

CMD_ACTIVEPANMODESETTING (#100)

0xFA 0x01 0x64 data-byte crc-low-byte crc-high-byte

The data is of type uint8_t and is a bit field related to the pan mode setting: default setting = 0x00, setting #1 = 0x01, setting #2 = 0x02, setting #3 = 0x03. As response to this command a CMD_ACK message will be emitted.

CMD_ACK (#150)

0xFB 0x01 0x96 data-byte crc-low-byte crc-high-byte

This command is send by the STorM32 controller to acknowledge execution of a received RC command message (if the message itself doesn't lead to a response, such as e.g. the get parameter command). The data is of type uint8_t and can assume these values:

0 = SERIALRCCMD_ACK_OK
1 = SERIALRCCMD_ACK_ERR_FAIL
2 = SERIALRCCMD_ACK_ERR_ACCESS_DENIED
3 = SERIALRCCMD_ACK_ERR_NOT_SUPPORTED
150 = SERIALRCCMD_ACK_ERR_TIMEOUT
151 = SERIALRCCMD_ACK_ERR_CRC 
152 = SERIALRCCMD_ACK_ERR_PAYLOADLEN

CMD_CONNECT (#210)

Deprecated.

CMD_GETDATADISPLAY (#213)

Deprecated.

CMD_WIFICONNECTEDPING (#215)

Deprecated.

CMD_STORM32LINK_V1 (#217)

Deprecated.

CMD_STORM32LINK_V2 (#218)

Special command: Is used for transmitting from a flight controller to the STorM32 for the STorM32-Link.

Mavlink Communication

In addition to the commands described in the previous sections, the STorM32 controller also understands MAVLink messages, as defined in the MAVLink standard. The STorM32 controller's MAVLink support is in fact quite rich, and quite complex, and actually provides two MAVLink components. Therefore, the description is placed in a separate article MAVLink Communication.

The STorM32's MAVLink Gimbal component is enabled by opening the [GUI:Interfaces Tool] window, which is accessible via the [GUI:Tools] menu, and setting Mavlink Gimbal to “Gimbal1”, which also sets the component ID. For further details see MAVLink Communication.

Code Examples

Please see Code Examples: Serial Communication.