/* * ---------------------------------------------------------------------------- * "THE BEER-WARE LICENSE" (Revision 42): * 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 * ---------------------------------------------------------------------------- */ /* $Id: twitest.c,v 1.6 2005/11/05 22:32:46 joerg_wunsch Exp $ */ /* * Simple demo program that talks to a 24Cxx I²C EEPROM using the * builtin TWI interface of an ATmega device. */ #include #include #include #include #include /* 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 */ /* * 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. * * 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; /* patch high bits of EEPROM address into SLA */ sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1); /* * 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 */ } 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; /* patch high bits of EEPROM address into SLA */ sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1); 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 */ } 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"); }