SMRD communication
Normally, the SMR C library copes with communication between a user's program and the SMR sensor daemon SMRD.
This page documents this communication.
Connect
SMRD listens for TCP/IP connections on port 24901. Multiple clients (up to ten) can be connected at once.
Data Packets
The communication protocol is byte oriented and binary coded.
Data both from client to server, and from server to client, is sent in packets. Each packet starts with a length byte, specifying the number of bytes to follow. For example:
0x04 0x10 0x20 0x30 0x40
Only the lower 5 bits of the first byte give the length. The upper 3 bits describe the source/destination of the packet:
0b000?????: RS485 master/slave serial bus 0b001?????: RS232 serial port 0b011?????: AU simulator packet 0b111?????: SMRD control packet
Poll
Clients start the communication by sending a client ready packet:
0xE1 0x02
The server responds with a number of packets. First, a start of period. This is followed by a series of data packets. Finally, an end of period packet is sent.
Start of period
0xE9 0x00 <sample no.>
Motor data
The two motors on an SMR are numbered 1 and 2. In the following, replace i with the motor number.
Some motor modules return more data than others. The length byte distinguishes between module types.
0x03 0xAi <encoder position> 0x05 0xAi <encoder position> <status> <pwm> <encoder position>: 2 byte (integer). 2000 positions per wheel turn. <status>: 1 byte status <pwm>: 1 byte motor drive voltage
MSB is to the left, for example: encoder position = 256*byte2 + byte3.
IR proximity data
0x09 0x88 <proximity data> <proximity data>: 8 bytes (array of bytes) proximity data. The first 6 bytes contain measurement data.
Serial line sensor
The serial port line sensor sends 16 bytes of sensor data; typically split into 2 or more packets. So, the length fields can vary from packet, and from sample to sample. A typical period might look like this:
0x27 0x73 <6 bytes serial data> 0x2B 0x73 <10 bytes serial data> <serial data>: Up to 16 bytes (array of bytes) serial data. The first 8 bytes contain measurement data.
Other packets may be received between serial port packets.
RS485 line sensor
0x09 0x17 <line sensor data> <line sensor data>: 8 bytes (array of bytes) line sensor data.
Power module
0x08 0x19 0b<fedcbaAA> 0b<BBCCDDEE> 0b<AAAAAAAA> 0b<BBBBBBBB> 0b<CCCCCCCC> 0b<DDDDDDDD> 0b<EEEEEEEE> fedcba: Digital input channels 5 to 0. AAAAAAAAAA...EEEEEEEEEE: Analog input (10 bits) channels 0 to 4. The two MSBs come from one of the pairs in byte 2 or 3. LSB is to the right.
The module inputs are connected as follows:
Digital input 0: Power on. Digital input 1...5: Unused. Analog input 0: Battery voltage. Analog input 1: External supply voltage. Analog input 2,3,4: Unused.
To convert analog input readings to volts:
Vin = 4.1 * 3.5 / 1.1 / 1024 * ADin
New Power Module v. 3.3b
Data is sent in same format as the old module
The module inputs are connected as follows:
Digital input 0 (a): Power on. Digital input 1 (b): External Power Connected. Digital input 2 (c): Robot is charging. Digital input 3..5 (d..f): Unused. Analog input 0 (A): Battery voltage. Analog input 1 (B): Robot Power Supply voltage. Analog input 2 (C): Battery charge current. Analog input 3 (D): Battery temperature sensor 1. Analog input 4 (E): Battery temperature sensor 2.
To convert analog input readings into usable values:
Battery voltage: Vbatt = 4.1 * 3.5 / 1.1 / 1024 * ADin. [V] Robot PSU voltage: Vpsu = 4.1 * 3.5 / 1.1 / 1024 * ADin. [V] Battery Chg Current: Ichg = ADin * 3 [mA]. Battery Temp 1 & 2: Tbatt = ADin [0.1 °C].
End of period
SMRD signals that the period is finished by sending end of period.
0xE1 0x01
No more packets will be sent to the client until a new poll is started.
Simulation time
When SMRdemo is connected to the simulator, it will receive the simulation time just before the end of period packet.
0x69 0x01 <simulation time> <simulation time>: 8 byte (double) simulation time.
