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/**
* Example sketch for writing to and reading from a slave in transactional manner
*
* NOTE: You must not use delay() or I2C communications will fail, use tws_delay() instead (or preferably some smarter timing system)
*
* On write the first byte received is considered the register addres to modify/read
* On each byte sent or read the register address is incremented (and it will loop back to 0)
*
* You can try this with the Arduino I2C REPL sketch at https://github.com/rambo/I2C/blob/master/examples/i2crepl/i2crepl.ino
* If you have bus-pirate remember that the older revisions do not like the slave streching the clock, this leads to all sorts of weird behaviour
*
* To read third value (register number 2 since counting starts at 0) send "[ 8 2 [ 9 r ]", value read should be 0xBE
* If you then send "[ 9 r r r ]" you should get 0xEF 0xDE 0xAD as response (demonstrating the register counter looping back to zero)
*
* You need to have at least 8MHz clock on the ATTiny for this to work (and in fact I have so far tested it only on ATTiny85 @8MHz using internal oscillator)
* Remember to "Burn bootloader" to make sure your chip is in correct mode
*/
/**
* Pin notes by Suovula, see also http://hlt.media.mit.edu/?p=1229
*
* DIP and SOIC have same pinout, however the SOIC chips are much cheaper, especially if you buy more than 5 at a time
* For nice breakout boards see https://github.com/rambo/attiny_boards
*
* Basically the arduino pin numbers map directly to the PORTB bit numbers.
*
// I2C
arduino pin 0 = not(OC1A) = PORTB <- _BV(0) = SOIC pin 5 (I2C SDA, PWM)
arduino pin 2 = = PORTB <- _BV(2) = SOIC pin 7 (I2C SCL, Analog 1)
// Timer1 -> PWM
arduino pin 1 = OC1A = PORTB <- _BV(1) = SOIC pin 6 (PWM)
arduino pin 3 = not(OC1B) = PORTB <- _BV(3) = SOIC pin 2 (Analog 3)
arduino pin 4 = OC1B = PORTB <- _BV(4) = SOIC pin 3 (Analog 2)
*/
#define I2C_SLAVE_ADDRESS 0x4 // the 7-bit address (remember to change this when adapting this example)
// Get this from https://github.com/rambo/TinyWire
#include <TinyWireS.h>
// The default buffer size, Can't recall the scope of defines right now
#ifndef TWI_RX_BUFFER_SIZE
#define TWI_RX_BUFFER_SIZE ( 16 )
#endif
volatile uint8_t i2c_regs[] =
{
0xDE,
0xAD,
0xBE,
0xEF,
};
// Tracks the current register pointer position
volatile byte reg_position;
const byte reg_size = sizeof(i2c_regs);
/**
* This is called for each read request we receive, never put more than one byte of data (with TinyWireS.send) to the
* send-buffer when using this callback
*/
void requestEvent()
{
TinyWireS.send(i2c_regs[reg_position]);
// Increment the reg position on each read, and loop back to zero
reg_position++;
if (reg_position >= reg_size)
{
reg_position = 0;
}
}
// TODO: Either update this to use something smarter for timing or remove it alltogether
void blinkn(uint8_t blinks)
{
digitalWrite(3, HIGH);
while(blinks--)
{
digitalWrite(3, LOW);
tws_delay(50);
digitalWrite(3, HIGH);
tws_delay(100);
}
}
/**
* The I2C data received -handler
*
* This needs to complete before the next incoming transaction (start, data, restart/stop) on the bus does
* so be quick, set flags for long running tasks to be called from the mainloop instead of running them directly,
*/
void receiveEvent(uint8_t howMany)
{
if (howMany < 1)
{
// Sanity-check
return;
}
if (howMany > TWI_RX_BUFFER_SIZE)
{
// Also insane number
return;
}
reg_position = TinyWireS.receive();
howMany--;
if (!howMany)
{
// This write was only to set the buffer for next read
return;
}
while(howMany--)
{
i2c_regs[reg_position] = TinyWireS.receive();
reg_position++;
if (reg_position >= reg_size)
{
reg_position = 0;
}
}
}
void setup()
{
// TODO: Tri-state this and wait for input voltage to stabilize
pinMode(3, OUTPUT); // OC1B-, Arduino pin 3, ADC
digitalWrite(3, LOW); // Note that this makes the led turn on, it's wire this way to allow for the voltage sensing above.
pinMode(1, OUTPUT); // OC1A, also The only HW-PWM -pin supported by the tiny core analogWrite
/**
* Reminder: taking care of pull-ups is the masters job
*/
TinyWireS.begin(I2C_SLAVE_ADDRESS);
TinyWireS.onReceive(receiveEvent);
TinyWireS.onRequest(requestEvent);
// Whatever other setup routines ?
digitalWrite(3, HIGH);
}
void loop()
{
/**
* This is the only way we can detect stop condition (http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&p=984716&sid=82e9dc7299a8243b86cf7969dd41b5b5#984716)
* it needs to be called in a very tight loop in order not to miss any (REMINDER: Do *not* use delay() anywhere, use tws_delay() instead).
* It will call the function registered via TinyWireS.onReceive(); if there is data in the buffer on stop.
*/
TinyWireS_stop_check();
}
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