mirror of
https://github.com/quorten/macsehw.git
synced 2024-06-04 16:29:29 +00:00
76760be8e6
* Convert to C. * Add simavr test/debug code. * Fix/improve 1-second timer pin. * Do not modify lastSerClock in clearState(). * Add pin change interrupt for serial clock, sleep during serial clock edges, build out PCINT0 ISR to handle watching for multiple pin changes on the same ISR.
473 lines
14 KiB
C
473 lines
14 KiB
C
/* Public Domain Dedication: CC0 1.0 Universal.
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For more information, please see
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<http://creativecommons.org/publicdomain/zero/1.0/>
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Developed with reference to a Reddit posting and Mini vMac source.
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* 2020-08-05: <https://www.reddit.com/r/VintageApple/comments/91e5cf/couldnt_find_a_replacement_for_the_rtcpram_chip/e2xqq60/>
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* 2020-09-04: <https://www.gryphel.com/d/minivmac/minivmac-36.04/minivmac-36.04.src.tgz>
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*/
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#include <avr/io.h>
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#include <avr/wdt.h>
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#include <avr/interrupt.h>
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#include <avr/sleep.h>
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#ifdef DO_SIMAVR
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#include "avr_mcu_section.h"
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AVR_MCU(32768, "attiny85");
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AVR_MCU_SIMAVR_COMMAND (& GPIOR0 );
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const struct avr_mmcu_vcd_trace_t _mytrace[] _MMCU_ =
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{
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{ AVR_MCU_VCD_SYMBOL("PORTB5"), .what = (void*)&PORTB, .mask = _BV(5) },
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};
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#endif
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/********************************************************************/
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// Simplified Arduino.h definitions.
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typedef enum { false, true } bool; // Compatibility with C++.
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typedef bool boolean;
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typedef uint8_t byte;
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#define bitRead(value, bit) (((value) >> (bit)) & 0x01)
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#define bitSet(value, bit) ((value) |= (1UL << (bit)))
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#define bitClear(value, bit) ((value) &= ~(1UL << (bit)))
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#define bitWrite(value, bit, bitvalue) ((bitvalue) ? bitSet(value, bit) : bitClear(value, bit))
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// END simplified Arduino.h definitions.
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/********************************************************************/
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/****************************************
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* *
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* A drop-in replacement for the custom *
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* RTC chip in early Apple Macintosh *
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* computers, using an ATtiny85. *
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* Uses an external 32.768kHz crystal *
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* on pins 2 and 3 as a clock source. *
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* __ __ *
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* 1SEC -|1 \/ 8|- VCC *
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* XTAL2 -|2 7|- RTC.CLK *
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* XTAL1 -|3 6|- RTC.DATA *
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* GND -|4____5|- !RTC *
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* *
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****************************************/
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/*********************************************
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* ATMEL ATTINY85 *
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* *
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* +-\/-+ *
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* Ain0 (D 5) PB5 1| |8 Vcc *
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* Ain3 (D 3) PB3 2| |7 PB2 (D 2) Ain1 *
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* Ain2 (D 4) PB4 3| |6 PB1 (D 1) pwm1 *
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* GND 4| |5 PB0 (D 0) pwm0 *
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* +----+ *
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*********************************************/
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const int ONE_SEC_PIN = 5; // A 1Hz square wave on PB5
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const int RTC_ENABLE_PIN = 0; // Active low chip enable on PB0
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const int SERIAL_DATA_PIN = 1; // Bi-directional serial data line on PB1
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const int SERIAL_CLOCK_PIN = 2; // Serial clock input on PB2
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#if NoXPRAM
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// Models earlier than the Plus had 20 bytes of PRAM
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//const int PRAM_SIZE = 20;
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#define PRAM_SIZE 20
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const int group1Base = 0x00;
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const int group2Base = 0x10;
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#else
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// Mac Plus used the xPRAM chip with 256 bytes
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//const int PRAM_SIZE = 256;
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#define PRAM_SIZE 256
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const int group1Base = 0x10;
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const int group2Base = 0x08;
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#endif
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enum SerialStateType { SERIAL_DISABLED, RECEIVING_COMMAND,
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SENDING_DATA, RECEIVING_DATA,
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RECEIVING_XCMD_ADDR, RECEIVING_XCMD_DATA };
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enum PramAddrResult { INVALID_CMD, SECONDS_CMD,
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WRTEST_CMD, WRPROT_CMD, SUCCESS_ADDR };
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volatile boolean lastRTCEnable = 0;
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volatile boolean lastSerClock = 0;
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volatile boolean serClockRising = false;
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volatile boolean serClockFalling = false;
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volatile enum SerialStateType serialState = SERIAL_DISABLED;
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volatile byte serialBitNum = 0;
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volatile byte address = 0;
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volatile byte serialData = 0;
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// Number of seconds since midnight, January 1, 1904. The serial
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// register interface exposes this data as little endian. TODO
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// VERIFY: Clock is initialized to January 1st, 1984? Or is this done
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// by the ROM when the validity status is invalid?
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volatile unsigned long seconds = 60UL * 60 * 24 * (365 * 4 + 1) * 20;
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volatile byte pram[PRAM_SIZE] = {}; // PRAM initialized as zeroed data
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volatile byte writeProtect = 0;
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#define shiftReadPB(output, bitNum, portBit) \
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bitWrite(output, bitNum, (PINB&_BV(portBit)) ? 1 : 0)
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void digitalWritePB(uint8_t pin, uint8_t val) {
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uint8_t bit = _BV(pin);
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cli();
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if (val == 0)
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PORTB &= ~bit;
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else
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PORTB |= bit;
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sei();
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}
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void setup(void) {
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cli(); // Disable interrupts while we set things up
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// OUTPUT: The 1Hz square wave (used for interrupts elsewhere in the system)
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DDRB |= ONE_SEC_PIN;
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// INPUT_PULLUP: The processor pulls this pin low when it wants access
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DDRB &= ~RTC_ENABLE_PIN;
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PORTB |= RTC_ENABLE_PIN;
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lastRTCEnable = PINB&(1<<RTC_ENABLE_PIN); // Initialize last value
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// INPUT_PULLUP: The serial clock is driven by the processor
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DDRB &= ~SERIAL_CLOCK_PIN;
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PORTB |= SERIAL_CLOCK_PIN;
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lastSerClock = PINB&(1<<SERIAL_CLOCK_PIN); // Initialize last value
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// INPUT_PULLUP: We'll need to switch this to output when sending data
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DDRB &= ~SERIAL_DATA_PIN;
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PORTB |= SERIAL_DATA_PIN;
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wdt_disable(); // Disable watchdog
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bitSet(ACSR, ACD); // Disable Analog Comparator, don't need it, saves power
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bitSet(PRR, PRTIM1); // Disable Timer 1, only using Timer 0, Timer 1 uses around ten times as much current
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bitSet(PRR, PRUSI); // Disable Universal Serial Interface, using Apple's RTC serial interface on pins 6 and 7
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bitSet(PRR, PRADC); // Disable Analog/Digital Converter
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bitSet(GIMSK, PCIE); // Pin Change Interrupt Enable
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bitSet(PCMSK, PCINT0); // turn on RTC enable interrupt
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bitSet(PCMSK, PCINT2); // turn on serial clock interrupt
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//set up timer
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bitSet(GTCCR, TSM); // Turns off timers while we set it up
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bitSet(TIMSK, TOIE0); // Set Timer/Counter0 Overflow Interrupt Enable
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// NOTE: 0b111 external clock, 0b011, uses 1/64 prescaler on I/O clock.
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TCCR0B = 0b011; // Set prescaler, 32,768Hz/64 = 512Hz, fills up the 8-bit counter (256) once every half second
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TCNT0 = 0; // Clear the counter
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bitClear(GTCCR, TSM); // Turns timers back on
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#ifdef DO_SIMAVR
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GPIOR0 = SIMAVR_CMD_VCD_START_TRACE;
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#endif
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sei(); //We're done setting up, enable those interrupts again
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}
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void clearState(void) {
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// Return the pin to input mode, set pullup resistor
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cli();
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DDRB &= ~SERIAL_DATA_PIN;
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PORTB |= SERIAL_DATA_PIN;
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sei();
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serialState = SERIAL_DISABLED;
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serialBitNum = 0;
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address = 0;
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serialData = 0;
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}
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/*
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* An interrupt to both increment the seconds counter and generate the
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* square wave
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*/
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void halfSecondInterrupt(void) {
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PINB = 1<<ONE_SEC_PIN; // Flip the one-second pin
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if (!(PINB&(1<<ONE_SEC_PIN))) { // If the one-second pin is low
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seconds++;
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// Make up for lost time, something around 6.4 cycles.
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TCNT0 += 6;
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}
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else
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TCNT0 += 7;
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}
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/*
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* The actual serial communication can be done in the main loop, this
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* way the clock still gets incremented.
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*/
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void handleRTCEnableInterrupt(void) {
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boolean curRTCEnable = PINB&(1<<RTC_ENABLE_PIN);
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if (lastRTCEnable && !curRTCEnable){ // Simulates a falling interrupt
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serialState = RECEIVING_COMMAND;
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// enableRTC = true;
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}
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/* Else if a rising edge to disable the RTC interrupts a serial
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communication in progress, we still wake up to clear the serial
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state then go back to sleep. */
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lastRTCEnable = curRTCEnable;
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}
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/*
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* Same deal over here, the actual serial communication can be done in
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* the main loop, this way the clock still gets incremented.
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*/
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void handleSerClockInterrupt(void) {
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boolean curSerClock = PINB&(1<<SERIAL_CLOCK_PIN);
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if (!lastSerClock && curSerClock) {
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serClockRising = true;
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serClockFalling = false;
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} else if (lastSerClock && !curSerClock) {
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serClockRising = false;
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serClockFalling = true;
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}
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/* Else leave it up to the main loop code to clear the edge trigger
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flags. */
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lastSerClock = curSerClock;
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}
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/*
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* For 20-byte PRAM equivalent commands, compute the actual PRAM
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* address by modifying the `address` variable in-place. Note that
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* `address` must have been already modified to remove the excess
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* bits. A status code is returned for commands that need special
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* processing:
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*
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* INVALID_CMD: Invalid command byte.
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* SECONDS_CMD: Special command: read seconds.
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* WRTEST_CMD: Special command: test write register.
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* WRPROT_CMD: Special command: write-protect register.
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* SUCCESS_ADDR: Successful address computation.
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*/
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uint8_t decodePramCmd(boolean writeRequest) {
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if (address < 8) {
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// Little endian clock data byte
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return SECONDS_CMD;
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} else if (address < 12) {
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// Group 2 register
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address = (address&0x03) + group2Base;
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} else if (address < 16) {
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if (writeRequest) {
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if (address == 12) // test write
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return WRTEST_CMD;
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if (address == 13) // write-protect
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return WRPROT_CMD;
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}
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return INVALID_CMD;
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} else {
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// Group 1 register
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address = (address&0x0f) + group1Base;
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}
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return SUCCESS_ADDR;
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}
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void loop(void) {
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if ((PINB&(1<<RTC_ENABLE_PIN))) {
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clearState();
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set_sleep_mode(0); // Sleep mode 0 == default, timers still running.
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sleep_mode();
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} else {
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/* Normally we only perform an action on the rising edge of the
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serial clock. The main exception is cleanup at the last cycle
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of serial output, there we wait until the falling edge before
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switching the direction of the data pin back to an input. */
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if (serClockFalling &&
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serialState == SENDING_DATA &&
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serialBitNum >= 8) {
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clearState();
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} else if (serClockRising) {
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boolean writeRequest;
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switch(serialState) {
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case RECEIVING_COMMAND:
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shiftReadPB(address, 7 - serialBitNum, SERIAL_DATA_PIN);
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serialBitNum++;
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if (serialBitNum <= 7)
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break;
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// The MSB determines if it's a write request or not.
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writeRequest = !(address&(1<<7));
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if ((address&0x78) == 0x38) {
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#if NoXPRAM
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// Invalid command.
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clearState();
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break;
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#else
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// This is an extended command, read the second address
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// byte.
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serialState = RECEIVING_XCMD_ADDR;
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serialBitNum = 0;
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break;
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#endif
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} else if (writeRequest) {
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// Read the data byte before continuing.
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serialState = RECEIVING_DATA;
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serialBitNum = 0;
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break;
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} else {
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boolean finished = false;
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// Discard the first bit and the last two bits, it's not
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// pertinent to command interpretation.
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address = (address&~(1<<7))>>2;
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// Decode the command/address.
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switch (decodePramCmd(writeRequest)) {
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case SECONDS_CMD:
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// Read little endian clock data byte.
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cli(); // Ensure that reads are atomic.
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address = (address&0x03)<<3;
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serialData = (seconds>>(address))&0xff;
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sei();
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break;
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case SUCCESS_ADDR:
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serialData = pram[address];
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break;
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case INVALID_CMD:
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default:
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finished = true;
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break;
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}
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if (finished) {
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clearState();
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break;
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}
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}
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// If we didn't break out early, send the output byte.
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serialState = SENDING_DATA;
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serialBitNum = 0;
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// Set the pin to output mode
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cli();
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DDRB |= SERIAL_DATA_PIN;
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sei();
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break;
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case RECEIVING_DATA:
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shiftReadPB(serialData, 7 - serialBitNum, SERIAL_DATA_PIN);
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serialBitNum++;
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if (serialBitNum <= 7)
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break;
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// Discard the first bit and the last two bits, it's not
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// pertinent to command interpretation.
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address = (address&~(1<<7))>>2;
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// Decode the command/address.
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switch (decodePramCmd(writeRequest)) {
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case SECONDS_CMD:
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if (!writeProtect) {
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// Write little endian clock data byte.
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cli(); // Ensure that writes are atomic.
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address = (address&0x03)<<3;
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seconds &= ~(0xff<<(address));
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seconds |= serialData<<(address);
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sei();
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}
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break;
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case WRPROT_CMD:
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// Update the write-protect register.
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writeProtect = (serialData & 0x80) ? 1 : 0;
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break;
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case SUCCESS_ADDR:
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if (!writeProtect)
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pram[address] = serialData;
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break;
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case WRTEST_CMD: // test write, do nothing
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case INVALID_CMD:
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default:
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break;
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}
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// Finished with the write command.
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clearState();
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break;
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case SENDING_DATA:
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digitalWritePB(SERIAL_DATA_PIN, bitRead(serialData, 7 - serialBitNum));
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serialBitNum++;
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/* if (serialBitNum <= 7)
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break; */
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/* NOTE: The last output cycle is treated specially, hold the
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data line as an output until the falling edge of the serial
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clock, then switch back to an input and reset the serial
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communication state. */
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break;
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#if !defined(NoXPRAM) || !NoXPRAM
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case RECEIVING_XCMD_ADDR:
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shiftReadPB(serialData, 7 - serialBitNum, SERIAL_DATA_PIN);
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serialBitNum++;
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if (serialBitNum <= 7)
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break;
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// The MSB determines if it's a write request or not.
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writeRequest = !(address&(1<<7));
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// Assemble the extended address.
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address = ((address&0x07)<<5) | ((serialData&0x7c)>>2);
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if (writeRequest) {
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serialState = RECEIVING_XCMD_DATA;
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serialBitNum = 0;
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break;
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}
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// Read and send the PRAM register.
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serialData = pram[address];
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serialState = SENDING_DATA;
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serialBitNum = 0;
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// Set the pin to output mode
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cli();
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DDRB |= SERIAL_DATA_PIN;
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sei();
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break;
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case RECEIVING_XCMD_DATA:
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shiftReadPB(serialData, 7 - serialBitNum, SERIAL_DATA_PIN);
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serialBitNum++;
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if (serialBitNum <= 7)
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break;
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// Write the PRAM register.
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pram[address] = serialData;
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// Finished with the write command.
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clearState();
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break;
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#endif
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default:
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// Invalid command.
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clearState();
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break;
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}
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}
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// Go to sleep until the next serial clock rising or falling edge.
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serClockRising = false;
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serClockFalling = false;
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set_sleep_mode(0); // Sleep mode 0 == default, timers still running.
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sleep_mode();
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}
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}
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/*
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* Actually attach the interrupt functions
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*/
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ISR(PCINT0_vect) {
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handleRTCEnableInterrupt();
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handleSerClockInterrupt();
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}
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ISR(TIMER0_OVF_vect) {
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halfSecondInterrupt();
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}
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// Arduino main function.
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int main(void) {
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setup();
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for (;;) {
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loop();
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}
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return 0;
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}
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