Microcontrollers

[Steve B]

Anyone here familiar with microcontrollers?
I'm coding up a program for an M16C, which doesn't have a temperature sensor onboard.
I'm required to create a random number generator, but as i have no timing capabilities, or no temperature sensor, i can't think of any way to pull a seed for the rand() function.

Anyone shed any light on this?

[DanceswithUnix]

Ideally you want to sample a noise source on an AtoD as that has known biasses (so not totally random) but is rather cheap.

How random do you need it? To security standards is Dead Hard.

If it is for user interaction of some sort then throwing away generated random numbers whilst waiting for a keypress can make it hard to predict the sequence even given the start value.

Look at the design and tot up any environmentally influenced inputs you might have.

[aidanjt]

Doesn't it have a clock generator you can use?
Generally speaking the more sources you can seed from the better.

[Steve B]

Its for a game of Simon (the one with 4 coloured lights and you have to follow the sequence)

So i need to produce 3 arrays of random numbers, 20,40 and 60 integers in length, depending on difficulty level set.

The arrays are initialised before the game is started, which is where i have the problem with my non-existant seed value. Every time I ran the program on the M16, it produced the same array.

I've thought about using the ADC register, but dont know how to access it I'm also considering using an external analogue influence, like the temperature sensor.

Cheers for the input chaps

[Steve B]

Doesn't it have a clock generator you can use?
Generally speaking the more sources you can seed from the better.

theres no timing on it at all, except for the timers that we initialise when the software is run. Hence, the array is executed at the same time every time, and the time seed is the same

[aidanjt]

theres no timing on it at all, except for the timers that we initialise when the software is run. Hence, the array is executed at the same time every time, and the time seed is the same

Well bugger :/

If you wanted to go the ADC register route, you could inline some assembly to access the register and assign it's value to your programs own register, nifty thing about inlining assembly is you don't need to worry about which register is yours, you just use the variable name you want to use and the compiler deals with the messy bits. I've never used the M16 before, so I can't be very specific, just tossing out some ideas that are generally relevant.

[Steve B]

i think i've stumbled across potentially the most efficient method:

1) Program Instantiation - Start
2) Activate Timer - every 5ms: i++
3) Wait for user to select options, choose difficulty level, e.g. 2 and push button.
4) Timer value used as seed

[aidanjt]

Ohhh, that'd work, simple, generic, relies on totally random user input.

[Steve B]

i know, i was rather pleased with myself