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// ---------------------------------
// Stress test program/example for TinyWireS I2C library.
// Run this slave program on the Attiny.
// Run the other master program on the Arduino Uno R3.
// ---------------------------------
// // Written by Scott Hartog, 2/6/2016, to stress test the TinyWireS library.
// https://github.com/rambo/TinyWire
//
// This project uses the Tiny85 as an I2C slave.
//
// The slave program using TinyWireS, running on a Attiny85, receives
// N bytes of random data in a single receiveEvent() callback and
// stores that data in a global buffer. It then responds the first requestEvent()
// callback with that same data. The requestEvent() callback overwrites the data
// buffer with zeros after responding so it will only respond correctly to the
// first requestEvent() callback after each receiveEvent() callback. Subsequent
// requestEvent() will respond with 0xff for all data bytes.
//
//
// SETUP:
// AtTiny Pin 5 (PB0/SDA) = I2C SDA
// connect to SDA on master with external pull-up (~4.7K)
// AtTiny Pin 7 (PB0/SCL) = I2C SCL
// connect to SCL on master with external pull-up (~4.7K)
// AtTiny Pin 1 (PB5/!RST)
// connect to reset on master (or just pull-up)
//
// Please see credits and usage for usiTwiSlave and TinyWireS in the .h files of
// those libraries.
#include <avr/sleep.h>
#include <avr/wdt.h>
#include "TinyWireS.h" // wrapper class for I2C slave routines
#define I2C_SLAVE_ADDR 0x26 // i2c slave address (38, 0x26)
// turns on code that makes the Tiny85 sleep between transactions
// This is optional. The Tiny85 current drops from
// about 2mA to about 20uA when the CPU is put into
// PowerDown sleep mode.
#define USE_CPU_SLEEP
// global buffer to store data sent from the master.
uint8_t master_data[16];
// global variable to number of bytes sent from the master.
uint8_t master_bytes;
// Gets called when the ATtiny receives an i2c write slave request
// This routine runs from the usiTwiSlave interrupt service routine (ISR)
// so interrupts are disabled while it runs.
void receiveEvent(uint8_t num_bytes)
{
uint8_t i;
// save the number of bytes sent from the master
master_bytes = num_bytes;
// store the data from the master into the data buffer
for (i = 0; i < master_bytes; i++)
master_data[i] = TinyWireS.receive();
}
// Gets called when the ATtiny receives an i2c read slave request
// This routine runs from the usiTwiSlave interrupt service routine (ISR)
// so interrupts are disabled while it runs.
void requestEvent()
{
uint8_t i;
// send the data buffer back to the master
for (i = 0; i < master_bytes; i++)
TinyWireS.send(master_data[i]);
// corrupt the byte values in the data buffer
// so that any subsequent call won't match
for (i = 0; i < master_bytes; i++)
master_data[i] += 0x5a;
// corrupt length of the request, but don't make it zero
// if the usiTwiSlave.c is working fine, then this number is completely irrelevant
// because the requestEvent() callback will not be called again until
// after the next receiveEvent() callback, so the master_data and
// master_bytes variables will be overwritten by that call.
// If the usiTwiSlave.c has the issue of calling the requestFrom() callback
// for each byte sent, the buffer will accumulate by this amount *for each byte
// in the original request*. (This problem is fixed in the recent version.)
//
// Making it zero will obscure the 1-byte send issue in the usiTwiSlave.c
// that is being tested.
// Making it small will allow a few requests to succeed before the tx buffer
// overflows and the usiTwiSlave.c hangs on the "while ( tmphead == txTail );"
// line
master_bytes = 2;
}
void setup()
{
//pinMode(1,OUTPUT); // This pin can be used for rudimentary debug
// initialize the TinyWireS and usiTwiSlave libraries
TinyWireS.begin(I2C_SLAVE_ADDR); // init I2C Slave mode
// register the onReceive() callback function
TinyWireS.onReceive(receiveEvent);
// register the onRequest() callback function
TinyWireS.onRequest(requestEvent);
// disable the watchdog timer so that it doesn't
// cause power-up, code is from datasheet
// Clear WDRF in MCUSR – MCU Status Register
// MCUSR provides information on which reset source caused an MCU Reset.
MCUSR = 0x00;
// WDTCR - Watchdog Timer Control Register
// Write logical one to WDCE and WDE (must be done before disabling)
WDTCR |= ( _BV(WDCE) | _BV(WDE) );
// Turn off WDT
WDTCR = 0x00;
#ifdef USE_CPU_SLEEP
// enable power down sleep mode
set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode
sleep_enable();
#endif
sei(); // enable interrupts
}
void loop()
{
#ifdef USE_CPU_SLEEP
// optionally put the CPU to sleep. It will be woken by a USI interrupt
// when it sees a "start condition" on the I2C bus. Everything interesting
// happens in the usiTwiSlave ISR.
sleep_cpu();
#endif
}
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