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* ----------------------------------------------------------------------------
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* "THE BEER-WARE LICENSE" (Revision 42):
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* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you think
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* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
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* ----------------------------------------------------------------------------
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/* $Id: twitest.c,v 1.2.2.2 2005/02/07 22:47:46 arcanum Exp $ */
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* Simple demo program that talks to a 24Cxx I�C EEPROM using the
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* builtin TWI interface of an ATmega device.
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#include <compat/twi.h> /* Note [1] */
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#define F_CPU 14745600UL /* Note [2] */
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* Compatibility defines. This should work on ATmega8, ATmega16,
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* ATmega163, ATmega323 and ATmega128 (IOW: on all devices that
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* provide a builtin TWI interface).
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* On the 128, it defaults to USART 1.
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# ifdef UCSR1A /* ATmega128 */
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* TWI address for 24Cxx EEPROM:
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* 1 0 1 0 E2 E1 E0 R/~W 24C01/24C02
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* 1 0 1 0 E2 E1 A8 R/~W 24C04
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* 1 0 1 0 E2 A9 A8 R/~W 24C08
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* 1 0 1 0 A10 A9 A8 R/~W 24C16
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#define TWI_SLA_24CXX 0xa0 /* E2 E1 E0 = 0 0 0 */
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* Maximal number of iterations to wait for a device to respond for a
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* selection. Should be large enough to allow for a pending write to
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* complete, but low enough to properly abort an infinite loop in case
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* a slave is broken or not present at all. With 100 kHz TWI clock,
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* transfering the start condition and SLA+R/W packet takes about 10
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* �s. The longest write period is supposed to not exceed ~ 10 ms.
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* Thus, normal operation should not require more than 100 iterations
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* to get the device to respond to a selection.
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* Number of bytes that can be written in a row, see comments for
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* ee24xx_write_page() below. Some vendor's devices would accept 16,
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* but 8 seems to be the lowest common denominator.
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* Note that the page size must be a power of two, this simplifies the
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* page boundary calculations below.
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* Saved TWI status register, for error messages only. We need to
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* save it in a variable, since the datasheet only guarantees the TWSR
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* register to have valid contents while the TWINT bit in TWCR is set.
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* Do all the startup-time peripheral initializations: UART (for our
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* debug/test output), and TWI clock.
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#if F_CPU <= 1000000UL
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* Slow system clock, double Baud rate to improve rate error.
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UBRR = (F_CPU / (8 * 9600UL)) - 1; /* 9600 Bd */
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UBRR = (F_CPU / (16 * 9600UL)) - 1; /* 9600 Bd */
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UCSRB = _BV(TXEN); /* tx enable */
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/* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
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/* has prescaler (mega128 & newer) */
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#if F_CPU < 3600000UL
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TWBR = 10; /* smallest TWBR value, see note [5] */
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TWBR = (F_CPU / 100000UL - 16) / 2;
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* Send character c down the UART Tx, wait until tx holding register
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loop_until_bit_is_set(UCSRA, UDRE);
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* Read "len" bytes from EEPROM starting at "eeaddr" into "buf".
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* This requires two bus cycles: during the first cycle, the device
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* will be selected (master transmitter mode), and the address
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* transfered. Address bits exceeding 256 are transfered in the
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* E2/E1/E0 bits (subaddress bits) of the device selector.
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* The second bus cycle will reselect the device (repeated start
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* condition, going into master receiver mode), and transfer the data
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* from the device to the TWI master. Multiple bytes can be
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* transfered by ACKing the client's transfer. The last transfer will
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* be NACKed, which the client will take as an indication to not
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* initiate further transfers.
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ee24xx_read_bytes(uint16_t eeaddr, int len, uint8_t *buf)
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uint8_t sla, twcr, n = 0;
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/* patch high bits of EEPROM address into SLA */
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sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1);
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* First cycle: master transmitter mode
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TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_REP_START: /* OK, but should not happen */
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case TW_MT_ARB_LOST: /* Note [9] */
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return -1; /* error: not in start condition */
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/* NB: do /not/ send stop condition */
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TWDR = sla | TW_WRITE;
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TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MT_SLA_NACK: /* nack during select: device busy writing */
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case TW_MT_ARB_LOST: /* re-arbitrate */
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goto error; /* must send stop condition */
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TWDR = eeaddr; /* low 8 bits of addr */
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TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MT_DATA_NACK:
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goto error; /* must send stop condition */
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* Next cycle(s): master receiver mode
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TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send (rep.) start condition */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_START: /* OK, but should not happen */
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TWDR = sla | TW_READ;
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TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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for (twcr = _BV(TWINT) | _BV(TWEN) | _BV(TWEA) /* Note [13] */;
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twcr = _BV(TWINT) | _BV(TWEN); /* send NAK this time */
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TWCR = twcr; /* clear int to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MR_DATA_NACK:
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len = 0; /* force end of loop */
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TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */
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* Write "len" bytes into EEPROM starting at "eeaddr" from "buf".
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* This is a bit simpler than the previous function since both, the
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* address and the data bytes will be transfered in master transmitter
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* mode, thus no reselection of the device is necessary. However, the
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* EEPROMs are only capable of writing one "page" simultaneously, so
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* care must be taken to not cross a page boundary within one write
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* cycle. The amount of data one page consists of varies from
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* manufacturer to manufacturer: some vendors only use 8-byte pages
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* for the smaller devices, and 16-byte pages for the larger devices,
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* while other vendors generally use 16-byte pages. We thus use the
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* smallest common denominator of 8 bytes per page, declared by the
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* macro PAGE_SIZE above.
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* The function simply returns after writing one page, returning the
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* actual number of data byte written. It is up to the caller to
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* re-invoke it in order to write further data.
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ee24xx_write_page(uint16_t eeaddr, int len, uint8_t *buf)
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if (eeaddr + len < (eeaddr | (PAGE_SIZE - 1)))
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endaddr = eeaddr + len;
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endaddr = (eeaddr | (PAGE_SIZE - 1)) + 1;
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len = endaddr - eeaddr;
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/* patch high bits of EEPROM address into SLA */
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sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1);
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TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_REP_START: /* OK, but should not happen */
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return -1; /* error: not in start condition */
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/* NB: do /not/ send stop condition */
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TWDR = sla | TW_WRITE;
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TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MT_SLA_NACK: /* nack during select: device busy writing */
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case TW_MT_ARB_LOST: /* re-arbitrate */
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goto error; /* must send stop condition */
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TWDR = eeaddr; /* low 8 bits of addr */
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TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MT_DATA_NACK:
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goto error; /* must send stop condition */
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for (; len > 0; len--)
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TWCR = _BV(TWINT) | _BV(TWEN); /* start transmission */
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while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */
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switch ((twst = TW_STATUS))
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case TW_MT_DATA_NACK:
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goto error; /* device write protected -- Note [16] */
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TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */
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* Wrapper around ee24xx_write_page() that repeats calling this
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* function until either an error has been returned, or all bytes
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ee24xx_write_bytes(uint16_t eeaddr, int len, uint8_t *buf)
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printf("Calling ee24xx_write_page(%d, %d, %p)",
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rv = ee24xx_write_page(eeaddr, len, buf);
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printf(" => %d\n", rv);
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printf("error: TWI status %#x\n", twst);
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fdevopen(uart_putchar, NULL, 0);
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for (a = 0; a < 256;)
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printf("%#04x: ", a);
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rv = ee24xx_read_bytes(a, 16, b);
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printf("warning: short read %d\n", rv);
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for (x = 0; x < rv; x++)
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printf("%02x ", b[x]);
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#define EE_WRITE(addr, str) ee24xx_write_bytes(addr, sizeof(str)-1, str)
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rv = EE_WRITE(55, "The quick brown fox jumps over the lazy dog.");
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printf("Wrote %d bytes.\n", rv);
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for (a = 0; a < 256;)
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printf("%#04x: ", a);
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rv = ee24xx_read_bytes(a, 16, b);
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printf("warning: short read %d\n", rv);
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for (x = 0; x < rv; x++)
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printf("%02x ", b[x]);
added
removed
doc/examples/twitest/twitest.c
