Thread: Need suggestions for control/variable storage structures

I am working on a embedded project using a Microchip PIC, a Radio Controlled robot lawnmower. I live on a farm and have a very large yard, you see - which I hope to eventually make autonomous. I want to be sure I make the program extensible. I have the basic functionality down (finally!), and am trying to expand my programming ability by incorporating additional features.

I am including a variety of error messages & display LEDs, for one thing, and am trying to figure out a logical hierarchy for controlling them. I will be using one or more Maxim MAX7221 SPI LED Controllers, and I plan to use one segment line from the '7221 per sub-system. I have the hardware working, no problems there, but I want to organize the control logic so it is uniform and expandable.

I am thinking about an array of structs, each made up of three other struct arrays, as follows:

Code:

#define NUMBER_OF_MOTORS      4 
#define NUMBER_OF_ENGINES     3 
#define NUMBER_OF_MCUS        7 

struct MOTOR[ NUMBER_OF_MOTORS ] { 
   temperature : 16 
   speed : 16 
   voltage : 8 
   current : 8 
   is_running : 1 
   is_over_voltage : 1 
   is_over_current : 1 
   is_over_temperature : 1 
   is_over_speed : 1 
   has_CAN_comms : 1 
   } 

struct ENGINE[ NUMBER_OF_ENGINES ] { 
   temperature : 16 
   speed : 16 
//   voltage : 8 
//   current : 8 
   is_running : 1 
//   over_voltage : 1 
//   over_current : 1 
   is_over_temperature : 1 
   is_over_speed : 1 
   has_CAN_comms : 1 
   } 

struct MCU[ NUMBER_OF_MCUS ] { 
   temperature : 16 
   voltage : 8 
   current : 8 
   has_power : 1 
   is_over_voltage : 1 
   is_over_current : 1 
   is_over_temperature : 1 
   has_CAN_comms : 1 
   } 

struct LOCATION[ item_location ] {   // e.g.   front_left.motor.temperature = 235 
   struct MOTOR[]                    // e.g.   middle_engine.mcu.has_power = TRUE 
   struct ENGINE[]                   // e.g.   master_mcu.has_CAN_comms = TRUE 
   struct MCU[]                      // e.g.   right_rear.motor.speed = 1250                  // Captured pulses 
   } 

//========================================== 

typedef enum { 
   rear_left, 
   front_left, 
   front_right, 
   rear_right, 
   left_engine, 
   middle_engine, 
   right_engine, 
   master_mcu, 
   engine_mcu, 
   contact_sensor_mcu 
   }; item_location

While this looks like it will work, it also looks like it will take up a lot of RAM. I have (a relatively large amount!) 3.8KB, but am already using half of it. Again, this is not a show stopper, as I am looking for something that works, but I also would like something that makes sense.

The actual members of the structs are not important as I am certain they will change as the execution is refined, but does this look like a reasonable solution?

Thanks for your time,
Brad

Originally Posted by Sergeant82d

I am working on a embedded project using a Microchip PIC, a Radio Controlled robot lawnmower.

I want one too!!!! I hope you also have a large fence, btw

Having never programmed an LED controller, I dunno how these fields are used. Why do you need 16-bit numbers for temp and speed? Isn't that a bit much?

This could be a lot of work if you have to keep downloading to hardware each time.
Abstraction (computer science) - Wikipedia, the free encyclopedia

Think about how you might prototype this on your PC.
For example,

Code:

#ifdef PC
void turnMotor ( int motorID, int direction, int numSteps ) {
  printf("Turning motor %d in direction %d for %d steps\n", motorID, direction, numSteps );
}
#else
void turnMotor ( int motorID, int direction, int numSteps ) {
  // here you write some bits to some I/O ports on the device to cause
  // a motor to turn.
}
#endif

Sensors are a little trickier; simple tests could be

Code:

#ifdef PC
// version 2 could read from a file of actual data recorded from
// your real device
int readTemperature ( int sensorID ) {
  static int samples[] = { 10, 11, 12, 3, 99, 12, 12, 13 };
  static int count = 0;
  int result = samples[count];
  count = ( count + 1 ) % 8;
  return result;
}
#else
int readTemperature ( int sensorID ) {
  // do something with a sensor, and return value
}
#endif

By creating a lot of little functions like these to describe the environment on the hardware, you should be able to get a LOT of testing done quite quickly on your PC. When you're happy with some progress, then recompile it for the target.

> I want to be sure I make the program extensible.
If you're that short on resources, go for something simple that works.
Extensibility comes with price tags (more CPU, more memory, more time to develop).

@ MK27 - I expect temps - at least on the engne - to be greater than 255; and the speed will be counting pulses from a gear-tooth sensor, which could be as high as 400 RPM x 64 pulses per revolution at full speed. Not while mowing, mind you... just while I'm joy-riding on it! To see my inspiration for this, see here: http://www.rediculouslygoodlooking.com/

@Salem - I do sincerely appreciate the advice regarding prototyping on the PC, but loading the firmware is not a problem... figuring out what to put in, and how to organize it is. I have been researching error handling, but have not located anything useful on writing a coherant overview of data.

Any further advice gratefully accepted!


// edited to add: I am using a number of functions such as you mention for sensors to collect data/command hardware; I really need help in storing and presenting the data in a comprehensive format. I apologize if I was not clear.