pins.md
Algorithm

PWM generation

PWM signal is generated by timers.

RPM measurement

RPM is measured by finding time between two RPM pulses using the 16-bit Timer1.
Pulses are detected using polling on input pins.

Atmega88 pin allocation




pin  1: reset, connected to VCC and protected by zener diode
pin  2: USART RX line (pullup?)
pin  3: USART TX line
pin  4: PD2, Error signal output
pin  5: PD3, OC2B, fan 4 PWM output
pin  6: PD4, not connected
pin  7: VCC
pin  8: GND
pin  9: XTAL 1
pin 10: XTAL 2
pin 11: PD5, OC0B, fan 2 PWM output
pin 12: PD6, OC0A, fan 1 PWM output
pin 13: PD7, not connected
pin 14: PB0, fan 1 enable
pin 15: PB1, fan 2 enable
pin 16: PB2, fan 3 enable
pin 17: PB3, fan 3 PWM output
pin 18: PB4, fan 4 enable
pin 19: PB5, not connected
pin 20: AVCC, connected to VCC through low-pass filter L1/C13
pin 21: AREF, analog reference, decoupled with 100nF cap C10
pin 22: GND
pin 23: PC0, ADC0, temperature sensor 1 input, low-pass filter R5/C7
pin 24: PC1, ADC1, temperature sensor 2 input, low-pass filter R3/C8
pin 25: PC2, fan 1 RPM input, pull-up, low-pass filter R10/C9
pin 26: PC3, fan 2 RPM input, pull-up, low-pass filter R9/C11
pin 27: PC4, fan 3 RPM input, pull-up, low-pass filter R8/C12
pin 28: PC5, fan 4 RPM input, pull-up, low-pass filter R7/C14


Port directions

Port B


PB0 - output (fan 1 enable)
PB1 - output (fan 2 enable)
PB2 - output (fan 3 enable)
PB3 - output (fan 3 PWM)
PB4 - output (fan 4 enable)
PB5 - output (not connected)
PB6 - output (overriden by xtal)
PB7 - output (overriden by xtal)


Port C


PC0 - input (ADC)
PC1 - input (ADC)
PC2 - input (fan 1 RPM, pull-up)
PC3 - input (fan 2 RPM, pull-up)
PC4 - input (fan 3 RPM, pull-up)
PC5 - input (fan 4 RPM, pull-up)
PC6 - input (default reset config)
PC7 - not in circuit/registry


Port D


PD0 - output (overriden by USART)
PD1 - output (overriden by USART)
PD2 - output (error)
PD3 - output (fan 4 PWM)
PD4 - output (not connected)
PD5 - output (fan 2 PWM)
PD6 - output (fan 1 PWM)
PD7 - output (not connected)


Fuses

Clock selection: full swing crystal


CKSEL 0111
SUT 11 (slow raising power)
Low fuse result: 0xf7


Registers


OSCCAL - Oscillator calibration register - NO CHANGE
CLKPR - Clock prescale register - NO CHANGE
SMCR - Sleep mode control register - NO CHANGE
PRR - Power reduction register - NO CHANGE
MCUSR - MCU status register - NO CHANGE
WDTCSR - Watchdog timer control register - NO CHANGE
MCUCR - MCU control register - interrupts through sei()
EICRA - External interrupt control register A - NO CHANGE
EIMSK - External interrupt mask register - NO CHANGE
EIFR - External interrupt flag register - NO CHANGE
PCICR - Pin change interrupt control register - NO CHANGE
PCIFR - Pin change interrupt flag register - NO CHANGE
PCMSK2 - Pin change mask register 2 - NO CHANGE
PCMSK1 - Pin change mask register 1 - NO CHANGE
PCMSK0 - Pin change mask register 0 - NO CHANGE
PINB - The port B input pins address - NOT USED
PIND - The port D input pins address - NOT USED
GTCCR - General timer/counter control register - NO CHANGE
SPCR – SPI control register - NO CHANGE
SPSR – SPI status register - NOT USED
SPDR – SPI data register - NOT USED


Port B


DDRB - The port B data direction register. As port B is
configured as output then all bit are set to 1.
PORTB - The port B data register. Used for controlling the fans.


Port C


DDRC - The port C data direction register- As port C is used as
input then no change is needed as it is configured as input by default.
PORTC - The port C data register. Some bits need to be written 1 to
enable pull-ups.
PINC - The port C input pins address. Used for polling fans PWM.


Port D


PORTD - The port D data register. Used for error signal. Other
functions are overriden (USART, PWM).
DDRD - The port D data direction register. As port B is configured
as output then all bit are set to 1.


Timer 0

Timer 0 needs to be configured in phase-correct PWM mode.


TCCR0A - Timer/counter control register A.
TCCR0B - Timer/counter control register B.
TCNT0 - Timer/counter register.
OCR0A - Output compare register A.
OCR0B - Output compare register B.
TIMSK0 - Timer/counter interrupt mask register - NO CHANGE
TIFR0 - Timer/Counter0 interrupt flag register - NO CHANGE


Timer 1

Timer 1 is used for counting time between RPM pulses and
detecting timeout.


TCCR1A – Timer/Counter1 control register A.
TCCR1B – Timer/Counter1 control register B.
TCCR1C – Timer/Counter1 control register C - NO CHANGE
TCNT1H and TCNT1L – Timer/Counter1.
OCR1AH and OCR1AL – Output compare register 1 A.
OCR1BH and OCR1BL – Output compare register 1 B.
ICR1H and ICR1L – Input capture register 1. NO CHANGE/NOT USED
TIMSK1 – Timer/Counter1 interrupt mask register
TIFR1 – Timer/Counter1 interrupt flag register


Timer 2

Timer 2 needs to be configured in phase-correct PWM mode.


TCCR2A – Timer/counter control register A.
TCCR2B – Timer/counter control register B.
TCNT2 – Timer/counter register.
OCR2A – Output compare register A.
OCR2B – Output compare register B.
TIMSK2 – Timer/Counter2 interrupt mask register - NO CHANGE
TIFR2 – Timer/Counter2 interrupt flag register - NO CHANGE
ASSR – Asynchronous status register - NO CHANGE


USART

TODO

ADC

ADC reference is set to AVcc.


ADCSRB – ADC Control and Status Register B - NO CHANGE
ACSR – Analog Comparator Control and Status Register - NO CHANGE
DIDR1 – Digital Input Disable Register 1 - NO CHANGE
ADMUX – ADC Multiplexer Selection Register
ADCSRA – ADC Control and Status Register A
ADCL and ADCH – The ADC Data Register
ADCSRB – ADC Control and Status Register B
DIDR0 – Digital Input Disable Register 0


FIXME - use watchdog?
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