18F series performance not so good?

[CuriousOne]

Hello to all survivors of too many redirects....

I finally got PIC18F45K80 running, and settings are correct - run multiple PAUSE statements and measured times with scope. But I'm not impressed with performance at all.

The simple code

SOME:
HIGH PORTB.1
LOW PORTB.1
GOTO SOME:

On the 16F series, outputs frequency that of 1/4 of OSC speed- say osc is 8mhz, output will be 2mhz and so on (and contrary some recomendations, replacing HIGH/LOW with LATB=X or TRISB=X does not improve the speed).

Now I have 18F45K80 running at 64mhz.

#config
CONFIG RETEN = OFF	
CONFIG INTOSCSEL = HIGH
CONFIG SOSCSEL = DIG
CONFIG XINST = ON	    ;Enabled
CONFIG FOSC = INTIO1
CONFIG PLLCFG = OFF
CONFIG FCMEN = OFF	    ;Disabled
CONFIG PWRTEN = OFF	    ;Disabled
CONFIG BOREN = OFF	    ;Disabled in hardware, SBOREN disabled
CONFIG WDTEN = OFF	    ;WDT disabled in hardware; SWDTEN bit disabled
CONFIG CANMX = PORTB
CONFIG MCLRE = OFF


#endconfig


OSCTUNE.6 = 1 ; Enable 4x PLL
OSCCON = %01110000
ANCON1=0 'DISABLE ADC D3-D2-D1-D0-
ancon0=0
TRISC=%00000000 'set PORTC as output all
TRISD=%00000000 'set PORTD as output all
TRISB=%00000000 'set PORTB as output all
TRISA=%00000000 'set PORTA 2 as input, others as output
TRISE=%0000000  'set PORTE as output all
define OSC 64
 
GKO:
HIGH PORTc.7
'PAUSEus 1
LOW PORTc.7
'PAUSEus 1
GOTO GKO

But output frequency is about 2.5mhz, but it should be at least 16mhz.

[Ioannis]

I do not have that chip and cannot test it.

But 16MHz cannot be output as the main clock is 64MHz and divided by 4 gives system clock of 16MHz. So each MCU tick is 62.5ns. I really do not know how many tick will take your program to execute, maybe 5 or 6? Worst case might be around 380ns or 2.6MHz.

Ioannis

[richard]

On the 16F series, outputs frequency that of 1/4 of OSC speed- say osc is 8mhz, output will be 2mhz and so on (and contrary some recomendations, replacing HIGH/LOW with LATB=X or TRISB=X does not improve the speed).

Not in my world a pic @8mhz [12,16 or 18] would get nowhere near that


GKO:
HIGH PORTc.7
LOW PORTc.7
GOTO GKO


TRANSLATES TO 5 LOOP instructions no matter whether its pic16 or pic18


GKO
BCF PORTC 7 1CYC
BCF PORTC+12H 7 1CYC
BSF PORTC 7 1CYC
BCF PORTC+12H 7 1CYC
BRA GKO 2CYC
AS IOANNIS states around 380ns or 2.66MHz @64MHZ




GKO:
LATC.7 = 0
LATC.7 = 1
GOTO GKO


TRANSLATES TO 3 LOOP instructions no matter whether its pic16 or pic18
GKO
BCF LATC 7 1CYC
BSF LATC 7 1CYC
BRA GKO 2CYC
around 250ns or 4MHz @64MHZ



DITTO FOR


LATC.7 = 0
GKO:
TRISC.7 = 0
TRISC.7 = 1
GOTO GKO


TRANSLATES TO 3 LOOP instructions no matter whether its pic16 or pic18
GKO
BCF TRISC 7 1CYC
BSF TRISC 7 1CYC
BRA GKO 2CYC
around 250ns or 4MHz @64MHZ

[tumbleweed]

I agree with richard. There's no way your numbers are correct, and directly using LAT vs HIGH/LOW should ALWAYS get you almost 2x the performance.

One thing in your setup... never set XINST=ON as it changes the way some instructions work.

CONFIG XINST = ON	<<<<<<<<<<<

[CuriousOne]

Well I posted all that several years ago, with the scope screenshots. Later I'll try to find that topic and bring it up.

So issue is, why 18F is so slow, and is there a way to fix it?

[tumbleweed]

It's not so slow... you're seeing what it should be.
The 16F isn't any faster. Since the max clock is 32MHz, it'll be half the speed.

If you want the 18F to be faster use LAT as Richard showed.