/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
* ----------------------------------------------------------------------------
*/
/*
* ----------------------------------------------------------------------------
* Updated to handle larger devices having 16-bit addresses
* (2007-09-05) Ruwan Jayanetti
* ----------------------------------------------------------------------------
*/
/* $Id: twitest.c 2187 2010-09-22 11:34:27Z aboyapati $ */
/*
* Simple demo program that talks to a 24Cxx I²C EEPROM using the
* builtin TWI interface of an ATmega device.
*/
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <avr/io.h>
#include <util/twi.h> /* Note [1] */
#define DEBUG 1
/*
* System clock in Hz.
*/
#define F_CPU 14745600UL /* Note [2] */
/*
* Compatibility defines. This should work on ATmega8, ATmega16,
* ATmega163, ATmega323 and ATmega128 (IOW: on all devices that
* provide a builtin TWI interface).
*
* On the 128, it defaults to USART 1.
*/
#ifndef UCSRB
# ifdef UCSR1A /* ATmega128 */
# define UCSRA UCSR1A
# define UCSRB UCSR1B
# define UBRR UBRR1L
# define UDR UDR1
# else /* ATmega8 */
# define UCSRA USR
# define UCSRB UCR
# endif
#endif
#ifndef UBRR
# define UBRR UBRRL
#endif
/*
* Note [3]
* TWI address for 24Cxx EEPROM:
*
* 1 0 1 0 E2 E1 E0 R/~W 24C01/24C02
* 1 0 1 0 E2 E1 A8 R/~W 24C04
* 1 0 1 0 E2 A9 A8 R/~W 24C08
* 1 0 1 0 A10 A9 A8 R/~W 24C16
*/
#define TWI_SLA_24CXX 0xa0 /* E2 E1 E0 = 0 0 0 */
/*
* Note [3a]
* Device word address length for 24Cxx EEPROM
* Larger EEPROM devices (from 24C32) have 16-bit address
* Define or undefine according to the used device
*/
//#define WORD_ADDRESS_16BIT
/*
* Maximal number of iterations to wait for a device to respond for a
* selection. Should be large enough to allow for a pending write to
* complete, but low enough to properly abort an infinite loop in case
* a slave is broken or not present at all. With 100 kHz TWI clock,
* transfering the start condition and SLA+R/W packet takes about 10
* µs. The longest write period is supposed to not exceed ~ 10 ms.
* Thus, normal operation should not require more than 100 iterations
* to get the device to respond to a selection.
*/
#define MAX_ITER 200
/*
* Number of bytes that can be written in a row, see comments for
* ee24xx_write_page() below. Some vendor's devices would accept 16,
* but 8 seems to be the lowest common denominator.
*
* Note that the page size must be a power of two, this simplifies the
* page boundary calculations below.
*/
#define PAGE_SIZE 8
/*
* Saved TWI status register, for error messages only. We need to
* save it in a variable, since the datasheet only guarantees the TWSR
* register to have valid contents while the TWINT bit in TWCR is set.
*/
uint8_t twst;
/*
* Do all the startup-time peripheral initializations: UART (for our
* debug/test output), and TWI clock.
*/
void
ioinit(void)
{
#if F_CPU <= 1000000UL
/*
* Note [4]
* Slow system clock, double Baud rate to improve rate error.
*/
UCSRA = _BV(U2X);
UBRR = (F_CPU / (8 * 9600UL)) - 1; /* 9600 Bd */
#else
UBRR = (F_CPU / (16 * 9600UL)) - 1; /* 9600 Bd */
#endif
UCSRB = _BV(TXEN); /* tx enable */
/* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
#if defined(TWPS0)
/* has prescaler (mega128 & newer) */
TWSR = 0;
#endif
#if F_CPU < 3600000UL
TWBR = 10; /* smallest TWBR value, see note [5] */
#else
TWBR = (F_CPU / 100000UL - 16) / 2;
#endif
}
/*
* Note [6]
* Send character c down the UART Tx, wait until tx holding register
* is empty.
*/
int
uart_putchar(char c, FILE *unused)
{
if (c == '\n')
uart_putchar('\r', 0);
loop_until_bit_is_set(UCSRA, UDRE);
UDR = c;
return 0;
}
/*
* Note [7]
*
* Read "len" bytes from EEPROM starting at "eeaddr" into "buf".
*
* This requires two bus cycles: during the first cycle, the device
* will be selected (master transmitter mode), and the address
* transfered.
* Address bits exceeding 256 are transfered in the
* E2/E1/E0 bits (subaddress bits) of the device selector.
* Address is sent in two dedicated 8 bit transfers
* for 16 bit address devices (larger EEPROM devices)
*
* The second bus cycle will reselect the device (repeated start
* condition, going into master receiver mode), and transfer the data
* from the device to the TWI master. Multiple bytes can be
* transfered by ACKing the client's transfer. The last transfer will
* be NACKed, which the client will take as an indication to not
* initiate further transfers.
*/
int
ee24xx_read_bytes(uint16_t eeaddr, int len, uint8_t *buf)
{
uint8_t sla, twcr, n = 0;
int rv = 0;
#ifndef WORD_ADDRESS_16BIT
/* patch high bits of EEPROM address into SLA */
sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1);
#else
/* 16-bit address devices need only TWI Device Address */
sla = TWI_SLA_24CXX;
#endif
/*
* Note [8]
* First cycle: master transmitter mode
*/
restart:
if (n++ >= MAX_ITER)
return -1;
begin:
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_REP_START: /* OK, but should not happen */
case TW_START:
break;
case TW_MT_ARB_LOST: /* Note [9] */
goto begin;
default:
return -1; /* error: not in start condition */
/* NB: do /not/ send stop condition */
}
/* Note [10] */
/* send SLA+W */
TWDR = sla | TW_WRITE;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_SLA_ACK:
break;
case TW_MT_SLA_NACK: /* nack during select: device busy writing */
/* Note [11] */
goto restart;
case TW_MT_ARB_LOST: /* re-arbitrate */
goto begin;
default:
goto error; /* must send stop condition */
}
#ifdef WORD_ADDRESS_16BIT
TWDR = (eeaddr >> 8); /* 16-bit word address device, send high 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_DATA_ACK:
break;
case TW_MT_DATA_NACK:
goto quit;
case TW_MT_ARB_LOST:
goto begin;
default:
goto error; /* must send stop condition */
}
#endif
TWDR = eeaddr; /* low 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_DATA_ACK:
break;
case TW_MT_DATA_NACK:
goto quit;
case TW_MT_ARB_LOST:
goto begin;
default:
goto error; /* must send stop condition */
}
/*
* Note [12]
* Next cycle(s): master receiver mode
*/
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send (rep.) start condition */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_START: /* OK, but should not happen */
case TW_REP_START:
break;
case TW_MT_ARB_LOST:
goto begin;
default:
goto error;
}
/* send SLA+R */
TWDR = sla | TW_READ;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MR_SLA_ACK:
break;
case TW_MR_SLA_NACK:
goto quit;
case TW_MR_ARB_LOST:
goto begin;
default:
goto error;
}
for (twcr = _BV(TWINT) | _BV(TWEN) | _BV(TWEA) /* Note [13] */;
len > 0;
len--)
{
if (len == 1)
twcr = _BV(TWINT) | _BV(TWEN); /* send NAK this time */
TWCR = twcr; /* clear int to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MR_DATA_NACK:
len = 0; /* force end of loop */
/* FALLTHROUGH */
case TW_MR_DATA_ACK:
*buf++ = TWDR;
rv++;
break;
default:
goto error;
}
}
quit:
/* Note [14] */
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */
return rv;
error:
rv = -1;
goto quit;
}
/*
* Write "len" bytes into EEPROM starting at "eeaddr" from "buf".
*
* This is a bit simpler than the previous function since both, the
* address and the data bytes will be transfered in master transmitter
* mode, thus no reselection of the device is necessary. However, the
* EEPROMs are only capable of writing one "page" simultaneously, so
* care must be taken to not cross a page boundary within one write
* cycle. The amount of data one page consists of varies from
* manufacturer to manufacturer: some vendors only use 8-byte pages
* for the smaller devices, and 16-byte pages for the larger devices,
* while other vendors generally use 16-byte pages. We thus use the
* smallest common denominator of 8 bytes per page, declared by the
* macro PAGE_SIZE above.
*
* The function simply returns after writing one page, returning the
* actual number of data byte written. It is up to the caller to
* re-invoke it in order to write further data.
*/
int
ee24xx_write_page(uint16_t eeaddr, int len, uint8_t *buf)
{
uint8_t sla, n = 0;
int rv = 0;
uint16_t endaddr;
if (eeaddr + len <= (eeaddr | (PAGE_SIZE - 1)))
endaddr = eeaddr + len;
else
endaddr = (eeaddr | (PAGE_SIZE - 1)) + 1;
len = endaddr - eeaddr;
#ifndef WORD_ADDRESS_16BIT
/* patch high bits of EEPROM address into SLA */
sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1);
#else
/* 16-bit address devices need only TWI Device Address */
sla = TWI_SLA_24CXX;
#endif
restart:
if (n++ >= MAX_ITER)
return -1;
begin:
/* Note [15] */
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_REP_START: /* OK, but should not happen */
case TW_START:
break;
case TW_MT_ARB_LOST:
goto begin;
default:
return -1; /* error: not in start condition */
/* NB: do /not/ send stop condition */
}
/* send SLA+W */
TWDR = sla | TW_WRITE;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_SLA_ACK:
break;
case TW_MT_SLA_NACK: /* nack during select: device busy writing */
goto restart;
case TW_MT_ARB_LOST: /* re-arbitrate */
goto begin;
default:
goto error; /* must send stop condition */
}
#ifdef WORD_ADDRESS_16BIT
TWDR = (eeaddr>>8); /* 16 bit word address device, send high 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_DATA_ACK:
break;
case TW_MT_DATA_NACK:
goto quit;
case TW_MT_ARB_LOST:
goto begin;
default:
goto error; /* must send stop condition */
}
#endif
TWDR = eeaddr; /* low 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_DATA_ACK:
break;
case TW_MT_DATA_NACK:
goto quit;
case TW_MT_ARB_LOST:
goto begin;
default:
goto error; /* must send stop condition */
}
for (; len > 0; len--)
{
TWDR = *buf++;
TWCR = _BV(TWINT) | _BV(TWEN); /* start transmission */
while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
switch ((twst = TW_STATUS))
{
case TW_MT_DATA_NACK:
goto error; /* device write protected -- Note [16] */
case TW_MT_DATA_ACK:
rv++;
break;
default:
goto error;
}
}
quit:
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */
return rv;
error:
rv = -1;
goto quit;
}
/*
* Wrapper around ee24xx_write_page() that repeats calling this
* function until either an error has been returned, or all bytes
* have been written.
*/
int
ee24xx_write_bytes(uint16_t eeaddr, int len, uint8_t *buf)
{
int rv, total;
total = 0;
do
{
#if DEBUG
printf("Calling ee24xx_write_page(%d, %d, %p)",
eeaddr, len, buf);
#endif
rv = ee24xx_write_page(eeaddr, len, buf);
#if DEBUG
printf(" => %d\n", rv);
#endif
if (rv == -1)
return -1;
eeaddr += rv;
len -= rv;
buf += rv;
total += rv;
}
while (len > 0);
return total;
}
void
error(void)
{
printf("error: TWI status %#x\n", twst);
exit(0);
}
FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);
void
main(void)
{
uint16_t a;
int rv;
uint8_t b[16];
uint8_t x;
ioinit();
stdout = &mystdout;
for (a = 0; a < 256;)
{
printf("%#04x: ", a);
rv = ee24xx_read_bytes(a, 16, b);
if (rv <= 0)
error();
if (rv < 16)
printf("warning: short read %d\n", rv);
a += rv;
for (x = 0; x < rv; x++)
printf("%02x ", b[x]);
putchar('\n');
}
#define EE_WRITE(addr, str) ee24xx_write_bytes(addr, sizeof(str)-1, str)
rv = EE_WRITE(55, "The quick brown fox jumps over the lazy dog.");
if (rv < 0)
error();
printf("Wrote %d bytes.\n", rv);
for (a = 0; a < 256;)
{
printf("%#04x: ", a);
rv = ee24xx_read_bytes(a, 16, b);
if (rv <= 0)
error();
if (rv < 16)
printf("warning: short read %d\n", rv);
a += rv;
for (x = 0; x < rv; x++)
printf("%02x ", b[x]);
putchar('\n');
}
printf("done.\n");
}
