create random values on PIC?

MIOS programming (C)
1

Hi all,

I need to create random values in the range 1-10 or so in my application. Is there an easy way to achieve this within the PIC?

Thanks, ilmenator

2

Well..

Many people have found this secret “hidden” function, by using compiled Midibox64 application and failing to reading the documentation :smiley:

I don’t know the software solution (see the examples), but if you leave analog input pin floating and read the value and scale it down to 1-10, would that be random enough?  ;D

Moebius

3

There’s already a RNG in MBSEQ :slight_smile:

;; --------------------------------------------------------------------------

;;  This function generates a new random number

;;  OUT: new random number in SEQ_RANDOM_SEED_[LH]

;; --------------------------------------------------------------------------

SEQ_CORE_GenRandomNumber

SET_BSR SEQ_BASE

movf SEQ_RANDOM_SEED_L, W, BANKED

mulwf SEQ_RANDOM_SEED_H, BANKED

movf TMR0L, W

addwf PRODL, W

movwf SEQ_RANDOM_SEED_L, BANKED

movlw 0x69

addwfc PRODH, W

movwf SEQ_RANDOM_SEED_H, BANKED

return

Scope the Humanizer functions out for a scaling example:

;; --------------------------------------------------------------------------

;;  this function applies a random value to a byte

;;  IN: pointer to byte in FSR1

;;      intensity in TMP1

;;  OUT: modified byte

;; --------------------------------------------------------------------------

SEQ_HUMANIZE_Modify

call SEQ_CORE_GenRandomNumber ; generate new random number

;; scale depending on intensity

rlf TMP2, W

rlf WREG, W

rlf WREG, W

andlw 0x78

mulwf SEQ_RANDOM_SEED_L, BANKED ; scaled result in PRODH

;; add/subtract depending on SEQ_RANDOM_SEED_H[0]

BIFCLR SEQ_RANDOM_SEED_H, 0, BANKED, rgoto SEQ_HUMANIZE_Modify_Add

SEQ_HUMANIZE_Modify_Sub

movf PRODH, W

subwf INDF1, W

;; saturate on overflow

IFSET WREG, 7, movlw 0x00

movwf INDF1

;; value should never be 0x00

movf INDF1, W

skpnz

incf INDF1, F

return

SEQ_HUMANIZE_Modify_Add

movf PRODH, W

addwf INDF1, W

;; saturate on overflow

IFSET WREG, 7, movlw 0x7f

movwf INDF1

return

:slight_smile: TK beat us to it again!

4

Okay,

thanks for that piece of code - I wouldn’t have found it, as I have no MBSEQ  :stuck_out_tongue:

Now, I don’t know much about Assembler, what does the code do? What is the range of the values that are created? How can I use it in my C code?

In my app generating the random values is not a real-time issue, so is there any other piece of [tt]C[/tt] code that might be easier to understand for me and which does the same?

Sorry for my ignorance, I’m still learning…  ::slight_smile:

Thanks a lot, ilmenator

5 
The "sid_random" application gets use of an external "real random" generator

In C, the "software random generator" in SEQ_CORE_GenRandomNumber function would look similar to this:
[code]
unsigned char random_seed_l;
unsigned char random_seed_h;

void gen_random_number(void)
{
  unsigned int tmp = random_seed_l * random_seed_h;
  random_seed_l = TMR0L + (unsigned char)(tmp & 0xff);
  random_seed_h = 0x69 + (unsigned char)(tmp >> 8);
}
[/code]


Maybe with some additional XOR operations the random value distribution could be improved, but I'm not an expert on this topic...

Best Regards, Thorsten.
[/code]