Speeding up a loop?

[richard]

(ex: =x*22/14-47/21249*x^2-7*x^3/(2^16) with x in binary radians has an error of about 1.7%, assuming I can implement it without being killed time-wise with DIV32)

.

on a esp8266 @ 160mhz clk or a esp32 , pic16fxx never

[tumbleweed]

audio tones up to 10kHz on a 16Fxx architecture with a 20Mhz OSC

16Fxx isn't the best choice

For comparison:
16Fxx @ 20MHz executes instructions at 5 MIPS,
16F1xxxx @ 32MHz -> 8 MIPS,
18F @ 64MHz -> 16 MIPS

Looking back at your original pseudo code with lookup table SINB array in ram:

loop1:
lookbyte=timebyte and 31
ampvar=SINB(lookbyte)
PORTB=ampvar
timebyte=timebyte+1
goto loop1

On a PIC18F @ 64MHz this executes in 1us/loop (1MHz update rate)
If you put the SINB table in ROM (which is more likely) it slows down to 1.25us/loop (800KHz update rate)

I didn't do those evaluations using PBP, so I don't know if it's much slower than that.

[richard]

a 16f648a@20mhz just passes 8khz with a 32 step lu in asm for a 4 bit r2r ladder on portb
my lu values may be dodgy i just guessed them, result looks awful @ any freq

#CONFIG  __config  _INTOSC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_OFF & _MCLRE_ON & _BODEN_ON & _LVP_OFF & _DATA_CP_OFF & _CP_OFF
#ENDCONFIG
    
DEFINE OSC 20 


inx var byte  bank0
trisb=%11110000
goto overasm
asm
    
table
    addwf   PCL, F                                          
    retlw    8
    retlw 	 9
    retlw    10
    retlw 	 11
    retlw    12
    retlw 	 13
    retlw    14
    retlw 	 14
    retlw 	 15
    retlw    14
    retlw 	 14
    retlw 	 13
    retlw    12
    retlw 	 11
    retlw    10
    retlw 	 9  
    retlw    8
    retlw    6
    retlw 	 5
    retlw 	 4  
    retlw    3
    retlw    2
    retlw 	 1   
    retlw 	 1
    retlw 	 0
    retlw 	 1   
    retlw 	 1
    retlw    2
    retlw    3
    retlw 	 4
    retlw 	 5
    retlw    6     
_lu  
    movf _inx ,w
    call table
    MOVE?AB PORTB
    RETURN
ENDASM         
overasm:
inx=0
loopp:
CALL lu
 inx=inx+1
 inx =inx&31 
goto loopp

[CuriousOne]

There is another approach. Check this video.

https://www.youtube.com/watch?v=ophqt_RmiS0

Code in description.

[Ioannis]

This guy has done unbelievable things with low end PIC and also a color video game with multi channel sound and VGA output on a PIC18F2550!
http://pic24.ru/doku.php/en/osa/articles/vga_game

Using an RTOS...

Ioannis

[CuriousOne]

Yeah, in his creations, 16F690 outperforms some guys with RPI

[Ioannis]

I dare to say that he is a Case Study! Wish I was proficient in C to run through his code.

Ioannis