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diff --git a/doc/6502_org_source_general_clockfreq.txt b/doc/6502_org_source_general_clockfreq.txt new file mode 100644 index 0000000..389d8a3 --- /dev/null +++ b/doc/6502_org_source_general_clockfreq.txt @@ -0,0 +1,201 @@ + [1][Return to Main Page] + + Calculation of Clock Frequency by Leo Nechaev + [2][Up to Source Code Repository] + __________________________________________________________________ + + This program calculates the clock frequency of 6502-based system. The + result is stored in location 'Ticks' to 'Ticks+3' in BCD representation + ('Ticks' - 2 symbols before decimal point, 'Ticks+1' to 'Ticks+3' - 6 + symbols after point), then result is sent via UART to the host (usually + PC with some kind of terminal programm). + + With minimal modifications (deleting 'SED' and 'CLD' instructions, + changing ticks constants [from BCD to binary format], deleting + 'terminal' subroutines) it may be used to determine real speed of + processor. +rgConfig = $6000 ; write: D6=1 - NMI is off, D6=0 - NMI is on +rgStatus = $6000 ; read: D6=0 - UART is busy +rgTxD = $5000 ; write: data to send via UART + +vcNMI = $FFFA + +Refresh = 450 ; NMI rate in Hz + + ldx #<NMI ; installing the NMI vector + ldy #>NMI + stx vcNMI + sty vcNMI+1 + lda #$40 ; on start NMI is off + sta InUse + +Again + lda #0 + sta Flag + sta Ticks ; initializing counter + sta Ticks+1 + sta Ticks+2 + sta Ticks+3 + lda #$FE ; initializing NMI counter (zeropoint minus 2 ti +cks) + sta Timer + lda #$FF + sta Timer+1 + lda InUse ; turn on NMI + and #$BF + sta rgConfig + sta InUse + +- bit Flag ; waiting for zeropoint minus 1 tick + bpl - + lda #0 + sta Flag + +- bit Flag ; waiting for true zeropoint + bpl - + lda #0 + sta Flag + +Main ; main counting cycle +;number of ticks per command sum of ticks +; v v + lda Ticks ;4 + clc ;2 6 + sed ;2 8 + adc #$53 ;2 10 + sta Ticks ;4 14 + lda Ticks+1 ;4 18 + adc #0 ;2 20 + sta Ticks+1 ;4 24 + lda Ticks+2 ;4 28 + adc #0 ;2 30 + sta Ticks+2 ;4 34 + lda Ticks+3 ;4 38 + adc #0 ;2 40 + sta Ticks+3 ;4 44 + cld ;2 46 + bit Flag ;4 50 + bpl Main ;3 53 + + lda #0 ;2 + sta Flag ;4 6 + lda Ticks ;4 10 + clc ;2 12 + sed ;2 14 + adc #$95 ;2 16 + sta Ticks ;4 20 + lda Ticks+1 ;4 24 + adc #0 ;2 26 + sta Ticks+1 ;4 30 + lda Ticks+2 ;4 34 + adc #0 ;2 36 + sta Ticks+2 ;4 40 + lda Ticks+3 ;4 44 + adc #0 ;2 46 + sta Ticks+3 ;4 50 + cld ;2 52 + lda Timer ;4 56 + cmp #<Refresh ;2 58 + bne Main ;3 61 + 34 (from NMI ISR) = 95 + lda Timer+1 ; 4 + cmp #>Refresh ; 2 + bne Main ; 3 + + lda InUse ; turn off NMI + ora #$40 + sta rgConfig + sta InUse + + ldx #0 ; send first string to the host +- lda Mes1,x + beq + + jsr Send + inx + jmp - + ++ lda Ticks+3 + pha + lsr + lsr + lsr + lsr + beq + ; delete non-significant zero (clock < 10MHz) + jsr PrintDigit ++ pla + and #15 + jsr PrintDigit + lda #"." ; decimal point + jsr Send + lda Ticks+2 + jsr PrintTwoDigits + lda Ticks+1 + jsr PrintTwoDigits + lda Ticks + jsr PrintTwoDigits + + ldx #0 ; send second string to the host +- lda Mes2,x + beq + + jsr Send + inx + jmp - ++ jmp Again ; repeat process + +PrintTwoDigits + pha + lsr + lsr + lsr + lsr + jsr PrintDigit + pla + and #15 + jsr PrintDigit + rts + +PrintDigit + ora #$30 + jsr Send + rts + +Send + bit rgStatus + bvc Send + sta rgTxD + rts + +Mes1 + .db 13 + .tx "Current clock frequency is " + .db 0 + +Mes2 + .tx " MHz" + .db 0 + +Ticks .br 4,0 +Timer .br 2,0 +InUse .db 0 +Flag .db 0 + +NMI ;6 + pha ;3 9 + inc Timer ;6 15 + bne + ;3 18 + inc Timer+1 ; 5 ++ lda #$80 ;2 20 + sta Flag ;4 24 + pla ;4 28 + rti ;6 34 + + Test results: + * with chip oscillator "1.8432" the result is '1.843266 MHz' + * with chip oscillator "20.000000M" and divider by 10 the result is + '2.000040 MHz' + + Last page update: December 27, 2000. + +References + + 1. http://6502.org/ + 2. http://6502.org/source |