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I am going to declare the front end of the detector to be finished. It has enough sensitivity to ID targets at a distance of one coil diameter. I think that will be enough for me to experiment with different motion filters and discrimination methods.
I think the front end code is stable enough now to start publishing it a piece at a time. This piece is part of the interrupt routine that drives the coil and demodulates the received signal.
There are some lines of code that are marked with the comment "debug". These lines play no part in the operation of the detector. They are just for diagnostic purposes.
Because timing is critical in this routine, some values are calculated ahead of time, during the previous interrupt. This makes the code difficult to understand. For example when I load a numeric value for the period of an interrupt, that is the value that will be stuffed in the timer the next time an interrupt occurs. Also an A/D conversion takes more than one quarter cycle to complete, so I cannot start a conversion and wait around for it to finish. I start a conversion and come back 3 interrupts later to pick up the results. So each time I call the A/D routine I am picking up results from a conversion I started 3 interrupts earlier and then starting a new conversion.
Some phases of the interrupt have to execute code that is common to other phases. So to conserve program memory, after one phase does something unique to that phase, it may jump to the code for another phase to execute common code.
Robert Hoolko
T2_Ovf: ; Timer2 Overflow Handler
; The T2 overflow interrupt is used to drive the transmit winding of
; the search coil and to read the receive signal and demodulate it.
; T2 is using a 4 usec clock, so each count of the clock or increment
; of the compare register is worth 4 usec.
; One cycle of the transmit signal is 152 usec or 38 counts.
; One quarter cycle should be 38/4 = 9.5 counts but only integers are
; allowed, so some quarter cycles will be 9 counts and others will
; be 10.
; The receive signal is sampled every 270 degrees.
; This routine goes through 12 phases for the 12 quarter cycles of the
; three full cycles it takes to get one full set of data for the
; demodulators.
out TCCR2,T2MODE ; quickly reload T2 for next interrupt
out OCR2,T2PW ;
out TCNT2,T2COUNT
sbi portc,5 ; debug,
push r18 ; save status and registers
in r18,sreg ;
push r18
push r17
push r16
push ZH
push ZL
; which interrupt phase are we in?
; calculate address to jump to
ldi ZL,low(T2jtab/2)
ldi ZH,high(T2jtab/2)
clr r16
add ZL,T2PHASE
adc ZH,r16
inc T2PHASE ; next phase
lds T2MODE,coiloff ; load default action
ijmp ; jump to code for this phase
T2jtab: ; Jump table
rjmp T2q0
rjmp T2q1
rjmp T2q2
rjmp T2q3
rjmp T2q4
rjmp T2q5
rjmp T2q6
rjmp T2q7
rjmp T2q8
rjmp T2q9
rjmp T2q10
rjmp T2q11
; The 12 interrupt phases
; ----- Q0 group (0 degrees) -----
T2q0:
ldi ZL,low(Itemp) ; demodulator I
ldi ZH,high(Itemp) ;
set ; say sub
rcall AD ; do A/D
rjmp T2q4
T2q8:
lds r16,Ichan ; set gain for next A/D
out ADMUX,r16
T2q4:
ldi r16,-10 ; next interrupt period
mov T2COUNT,r16
ldi r16,0 ; coil drive, sub 0
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q1 group (90 degrees) -----
T2q9:
ldi ZL,low(Qtemp) ; demodulator Q
ldi ZH,high(Qtemp) ;
clt ; say add
rcall AD ; do A/D
rjmp T2q1
T2q5:
lds r16,Qchan ; set gain for next A/D
out ADMUX,r16
T2q1:
ldi r16,-10 ; next interrupt period
mov T2COUNT,r16
ldi r16,-28 ; coil drive, sub 28
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q2 group (180 degrees) -----
T2q6:
ldi ZL,low(Itemp) ; demodulator I
ldi ZH,high(Itemp) ;
clt ; say add
rcall AD ; do A/D
rjmp T2q10
T2q2:
lds r16,Ichan ; set gain for next A/D
out ADMUX,r16
T2q10:
ldi r16,-9 ; next interrupt period
mov T2COUNT,r16
ldi r16,-19 ; coil drive, sub 19
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q3 group (270 degrees) -----
T2q3:
ldi ZL,low(Qtemp) ; demodulator Q
ldi ZH,high(Qtemp) ;
set ; say sub
rcall AD ; do A/D
rjmp T2q7
T2q11:
clr T2PHASE ; phase 0
lds r16,Qchan ; set gain for next A/D
out ADMUX,r16
T2q7:
ldi r16,-9 ; next interrupt period
mov T2COUNT,r16
ldi r16,-10 ; coil drive, sub 10
mov T2PW,r16 ; put it here temporarily
; rjmp T2end1
; ----- end of interrupt phases -----
T2end1:
;finish seting up T2 pulse width
lds r16,drvangle ; coil drive angle
add r16,T2PW ; modify
sbrc r16,7 ; skip if positive
subi r16,-38 ; else add 38 to make pos
cpi r16,19 ; if >= 19
brlt T2end2
subi r16,19 ; wrap and
ldi r17,00010000b ; invert action
eor T2MODE,r17
T2end2:
mov T2PW,r16
neg T2PW ; T2 counts up
tst T2PHASE ; is it time to count 2200dths?
brne T2_Ovf_out
rcall count2200 ; count 2200dths of a sec
T2_Ovf_out:
pop ZL ; restore registers and status
pop ZH
pop r16
pop r17
pop r18
out sreg,r18
pop r18
cbi portc,5 ; debug,
reti
I think the front end code is stable enough now to start publishing it a piece at a time. This piece is part of the interrupt routine that drives the coil and demodulates the received signal.
There are some lines of code that are marked with the comment "debug". These lines play no part in the operation of the detector. They are just for diagnostic purposes.
Because timing is critical in this routine, some values are calculated ahead of time, during the previous interrupt. This makes the code difficult to understand. For example when I load a numeric value for the period of an interrupt, that is the value that will be stuffed in the timer the next time an interrupt occurs. Also an A/D conversion takes more than one quarter cycle to complete, so I cannot start a conversion and wait around for it to finish. I start a conversion and come back 3 interrupts later to pick up the results. So each time I call the A/D routine I am picking up results from a conversion I started 3 interrupts earlier and then starting a new conversion.
Some phases of the interrupt have to execute code that is common to other phases. So to conserve program memory, after one phase does something unique to that phase, it may jump to the code for another phase to execute common code.
Robert Hoolko
T2_Ovf: ; Timer2 Overflow Handler
; The T2 overflow interrupt is used to drive the transmit winding of
; the search coil and to read the receive signal and demodulate it.
; T2 is using a 4 usec clock, so each count of the clock or increment
; of the compare register is worth 4 usec.
; One cycle of the transmit signal is 152 usec or 38 counts.
; One quarter cycle should be 38/4 = 9.5 counts but only integers are
; allowed, so some quarter cycles will be 9 counts and others will
; be 10.
; The receive signal is sampled every 270 degrees.
; This routine goes through 12 phases for the 12 quarter cycles of the
; three full cycles it takes to get one full set of data for the
; demodulators.
out TCCR2,T2MODE ; quickly reload T2 for next interrupt
out OCR2,T2PW ;
out TCNT2,T2COUNT
sbi portc,5 ; debug,
push r18 ; save status and registers
in r18,sreg ;
push r18
push r17
push r16
push ZH
push ZL
; which interrupt phase are we in?
; calculate address to jump to
ldi ZL,low(T2jtab/2)
ldi ZH,high(T2jtab/2)
clr r16
add ZL,T2PHASE
adc ZH,r16
inc T2PHASE ; next phase
lds T2MODE,coiloff ; load default action
ijmp ; jump to code for this phase
T2jtab: ; Jump table
rjmp T2q0
rjmp T2q1
rjmp T2q2
rjmp T2q3
rjmp T2q4
rjmp T2q5
rjmp T2q6
rjmp T2q7
rjmp T2q8
rjmp T2q9
rjmp T2q10
rjmp T2q11
; The 12 interrupt phases
; ----- Q0 group (0 degrees) -----
T2q0:
ldi ZL,low(Itemp) ; demodulator I
ldi ZH,high(Itemp) ;
set ; say sub
rcall AD ; do A/D
rjmp T2q4
T2q8:
lds r16,Ichan ; set gain for next A/D
out ADMUX,r16
T2q4:
ldi r16,-10 ; next interrupt period
mov T2COUNT,r16
ldi r16,0 ; coil drive, sub 0
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q1 group (90 degrees) -----
T2q9:
ldi ZL,low(Qtemp) ; demodulator Q
ldi ZH,high(Qtemp) ;
clt ; say add
rcall AD ; do A/D
rjmp T2q1
T2q5:
lds r16,Qchan ; set gain for next A/D
out ADMUX,r16
T2q1:
ldi r16,-10 ; next interrupt period
mov T2COUNT,r16
ldi r16,-28 ; coil drive, sub 28
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q2 group (180 degrees) -----
T2q6:
ldi ZL,low(Itemp) ; demodulator I
ldi ZH,high(Itemp) ;
clt ; say add
rcall AD ; do A/D
rjmp T2q10
T2q2:
lds r16,Ichan ; set gain for next A/D
out ADMUX,r16
T2q10:
ldi r16,-9 ; next interrupt period
mov T2COUNT,r16
ldi r16,-19 ; coil drive, sub 19
mov T2PW,r16 ; put it here temporarily
rjmp T2end1
; ----- Q3 group (270 degrees) -----
T2q3:
ldi ZL,low(Qtemp) ; demodulator Q
ldi ZH,high(Qtemp) ;
set ; say sub
rcall AD ; do A/D
rjmp T2q7
T2q11:
clr T2PHASE ; phase 0
lds r16,Qchan ; set gain for next A/D
out ADMUX,r16
T2q7:
ldi r16,-9 ; next interrupt period
mov T2COUNT,r16
ldi r16,-10 ; coil drive, sub 10
mov T2PW,r16 ; put it here temporarily
; rjmp T2end1
; ----- end of interrupt phases -----
T2end1:
;finish seting up T2 pulse width
lds r16,drvangle ; coil drive angle
add r16,T2PW ; modify
sbrc r16,7 ; skip if positive
subi r16,-38 ; else add 38 to make pos
cpi r16,19 ; if >= 19
brlt T2end2
subi r16,19 ; wrap and
ldi r17,00010000b ; invert action
eor T2MODE,r17
T2end2:
mov T2PW,r16
neg T2PW ; T2 counts up
tst T2PHASE ; is it time to count 2200dths?
brne T2_Ovf_out
rcall count2200 ; count 2200dths of a sec
T2_Ovf_out:
pop ZL ; restore registers and status
pop ZH
pop r16
pop r17
pop r18
out sreg,r18
pop r18
cbi portc,5 ; debug,
reti