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#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdlib.h>
/*
* Onewire iButton / SmartButton slave.
* Has the 64bit ID set below
* (corresponds to <https://wiki.chaosdorf.de/images/f/fc/Smartbutton.jpg>).
* Note: The bytes are sent in reversed order. This has also been observed
* on off-the-shelf smartbuttons / iButtons.
*
* Only supports non-overdrive READ ROM. Does not hold any data.
* SEARCH ROM Support is work in progress. Command byte readout is pretty
* broken right now.
*
* Tested and working with a DS2482. Should mostly adhere to the standard,
* but nothing is guaranteed.
*/
#define ADDR1 0xC4
#define ADDR2 0x00
#define ADDR3 0x00
#define ADDR4 0x09
#define ADDR5 0x7d
#define ADDR6 0x79
#define ADDR7 0x04
#define ADDR8 0x01
// HCNT: r30 (ZL), r31 (ZH)
// LCNT: r28 (YL), r29 (YH)
#define LCNTH GPIOR2
#define LCNTL GPIOR1
#define HCNTL GPIOR0
#define CNT USIDR
#define LASTCMD OCR0B
#define BUF OCR0A
#define POS OCR1A
#define APOS OCR1B
#define BYTE EEDR
int main (void)
{
/* watchdog reset after ~4 seconds */
MCUSR &= ~_BV(WDRF);
WDTCSR = _BV(WDCE) | _BV(WDE);
WDTCSR = _BV(WDE) | _BV(WDP3);
MCUCR = _BV(ISC10);
GIMSK = _BV(INT1);
ACSR |= _BV(ACD);
POS = 0;
APOS = 0;
DDRD = 0;
PORTD = 0;
sei();
asm volatile ("ldi r28, 0");
asm volatile ("ldi r29, 0");
asm volatile ("ldi r30, 0");
asm volatile ("ldi r31, 0");
// 1us per cycle
loop:
asm volatile ("inc r30"); // 1c
asm volatile ("adiw r28, 1"); // 2c
asm volatile ("wdr"); // 1c
asm volatile ("nop"); // 1c
asm volatile ("nop"); // 1c
asm volatile ("nop"); // 1c
goto loop;
return 0;
}
ISR(INT1_vect)
{
// overhead: 19c (2.4us)
if (PIND & _BV(PD3)) {
asm volatile ("out 0x15, r29"); // LCNTH
asm volatile ("out 0x14, r28"); // LCNTL
asm volatile ("out 0x13, r30"); // HCNTL
// > 256us - reset
if (LCNTH > 0) {
DDRD = _BV(PD3);
// 120us loop - r31 / r30 need not be preserved
asm volatile ("ldi r31, 0");
asm volatile ("ldi r30, 120"); // Z = 120
asm volatile ("wdr"); // <-----
asm volatile ("wdr");
asm volatile ("wdr");
asm volatile ("sbiw r30, 1");
asm volatile ("cp r30, r1");
asm volatile ("brne .-12"); // -^
DDRD = 0;
LASTCMD = 0;
BUF = 0;
POS = 0;
asm volatile ("wdr");
EIFR |= _BV(INTF1);
}
// ~60us - write 0
else if (LCNTL > 15) {
if (!LASTCMD)
POS++;
}
// < ~15us - write 1 OR read
else {
if (!LASTCMD) {
BUF |= _BV(POS);
POS++;
}
}
if (!LASTCMD && (POS == 7)) {
LASTCMD = BUF;
POS = 1;
APOS = 0;
BYTE = ~ADDR8;
EEAR = 0;
EIFR |= _BV(INTF1);
}
asm volatile ("ldi r30, 1"); // HCNTL = 1
}
else {
if (LASTCMD == 0x33) {
if (BYTE & POS) {
DDRD = _BV(PD3);
// 15us loop - r31 / r30 need not be preserved
asm volatile ("ldi r31, 0");
asm volatile ("ldi r30, 15"); // Z = 120
asm volatile ("wdr"); // <-----
asm volatile ("wdr");
asm volatile ("wdr");
asm volatile ("sbiw r30, 1");
asm volatile ("cp r30, r1");
asm volatile ("brne .-12"); // -^
DDRD = 0;
asm volatile ("wdr");
EIFR |= _BV(INTF1);
}
if (POS != 0x80) {
POS <<= 1;
}
else {
APOS++;
POS = 1;
if (APOS == 1)
BYTE = ~ADDR7;
else if (APOS == 2)
BYTE = ~ADDR6;
else if (APOS == 3)
BYTE = ~ADDR5;
else if (APOS == 4)
BYTE = ~ADDR4;
else if (APOS == 5)
BYTE = ~ADDR3;
else if (APOS == 6)
BYTE = ~ADDR2;
else if (APOS == 7)
BYTE = ~ADDR1;
else if (APOS == 8) {
LASTCMD = 0;
POS = 0;
}
}
}
else if (LASTCMD == 0xf0) {
if (((EEAR == 0) && (BYTE & POS))
|| ((EEAR == 1) && !(BYTE & POS))) {
//if (BYTE & POS) {
DDRD = _BV(PD3);
// 15us loop - r31 / r30 need not be preserved
asm volatile ("ldi r31, 0");
asm volatile ("ldi r30, 15"); // Z = 120
asm volatile ("wdr"); // <-----
asm volatile ("wdr");
asm volatile ("wdr");
asm volatile ("sbiw r30, 1");
asm volatile ("cp r30, r1");
asm volatile ("brne .-12"); // -^
DDRD = 0;
asm volatile ("wdr");
EIFR |= _BV(INTF1);
}
if (EEAR < 2) {
EEAR++;
}
else if (POS != 0x80) {
POS <<= 1;
EEAR = 0;
}
else {
EEAR = 0;
APOS++;
POS = 1;
if (APOS == 1)
BYTE = ~ADDR7;
else if (APOS == 2)
BYTE = ~ADDR6;
else if (APOS == 3)
BYTE = ~ADDR5;
else if (APOS == 4)
BYTE = ~ADDR4;
else if (APOS == 5)
BYTE = ~ADDR3;
else if (APOS == 6)
BYTE = ~ADDR2;
else if (APOS == 7)
BYTE = ~ADDR1;
else if (APOS == 8) {
LASTCMD = 0;
POS = 0;
}
}
}
asm volatile ("ldi r29, 0"); // LCNTH = 0
asm volatile ("ldi r28, 1"); // LCNTL = 1
}
}
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