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#include <avr/io.h>
#include <stdlib.h>
#include "storage.h"
Storage storage;
/*
* EEPROM data structure ("file system"):
*
* Organized as 64B-pages, all animations/texts are page-aligned. Byte 0 ..
* 255 : storage metadata. Byte 0 contains the number of animations, byte 1 the
* page offset of the first animation, byte 2 of the second, and so on.
* Byte 256+: texts/animations without additional storage metadata, aligned
* to 64B. So, a maximum of 256-(256/64) = 252 texts/animations can be stored,
* and a maximum of 255 * 64 = 16320 Bytes (almost 16 kB / 128 kbit) can be
* addressed. To support larger EEPROMS, change the metadate area to Byte 2 ..
* 511 and use 16bit page pointers.
*
* The text/animation size is not limited by this approach.
*
* Example:
* Byte 0 = 3 -> we've got a total of three animations
* Byte 1 = 4 -> first text/animation starts at byte 64*4 = 256
* Byte 2 = 8 -> second starts at byte 64*8 = 512
* Byte 3 = 9 -> third starts at 64*9 * 576
* Byte 4 = whatever
* .
* .
* .
* Byte 256ff = first text/animation. Has a header encoding its length in bytes.
* Byte 512ff = second
* Byte 576ff = third
* .
* .
* .
*/
void Storage::enable()
{
/*
* Set I2C clock frequency to 100kHz.
* freq = F_CPU / (16 + (2 * TWBR * TWPS) )
* let TWPS = "00" = 1
* -> TWBR = (F_CPU / 100000) - 16 / 2
*/
TWSR = 0; // the lower two bits control TWPS
TWBR = ((F_CPU / 100000UL) - 16) / 2;
}
/*
* Send an I2C (re)start condition and the EEPROM address in read mode. Returns
* after it has been transmitted successfully.
*/
void Storage::i2c_start_read()
{
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
while (!(TWCR & _BV(TWINT)));
// Note: The R byte ("... | 1") causes the TWI momodule to switch to
// Master Receive mode
TWDR = (I2C_EEPROM_ADDR << 1) | 1;
TWCR = _BV(TWINT) | _BV(TWEN);
while (!(TWCR & _BV(TWINT)));
}
/*
* Send an I2C (re)start condition and the EEPROM address in write mode.
* Returns after it has been transmitted successfully.
*/
void Storage::i2c_start_write()
{
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN);
while (!(TWCR & _BV(TWINT)));
TWDR = (I2C_EEPROM_ADDR << 1) | 0;
TWCR = _BV(TWINT) | _BV(TWEN);
while (!(TWCR & _BV(TWINT)));
}
/*
* Send an I2C stop condition.
*/
void Storage::i2c_stop()
{
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN);
}
/*
* Sends len bytes to the EEPROM. Note that this method does NOT
* send I2C start or stop conditions.
*/
// TODO Everything[tm] (error handling and generic code)
int8_t Storage::i2c_send(uint8_t len, uint8_t *data)
{
uint8_t pos = 0;
for (pos = 0; pos < len; pos++) {
TWDR = data[pos];
TWCR = _BV(TWINT) | _BV(TWEN);
while (!(TWCR & _BV(TWINT)));
}
return pos + 1;
}
/*
* Receives len bytes from the EEPROM into data. Note that this method does
* NOT send I2C start or stop conditions.
*/
// TODO dito
int8_t Storage::i2c_receive(uint8_t len, uint8_t *data)
{
uint8_t pos = 0;
for (pos = 0; pos < len; pos++) {
if (pos == len-1) {
// Don't ACK the last byte
TWCR = _BV(TWINT) | _BV(TWEN);
} else {
// Automatically send ACK
TWCR = _BV(TWINT) | _BV(TWEN) | _BV(TWEA);
}
while (!(TWCR & _BV(TWINT)));
data[pos] = TWDR;
}
return pos + 1;
}
/*
* Writes len bytes of data into the EEPROM, starting at byte number pos.
* Does not check for page boundaries yet.
* Includes a complete I2C transaction.
*/
int8_t Storage::i2c_write(uint16_t pos, uint8_t len, uint8_t *data)
{
uint8_t addr_buf[2];
addr_buf[0] = pos >> 8;
addr_buf[1] = pos & 0xff;
i2c_start_write();
i2c_send(2, addr_buf);
i2c_send(len, data);
i2c_stop();
return 0; // TODO proper return code to indicate write errors
}
/*
* Reads len bytes of data from the EEPROM, starting at byte number pos.
* Does not check for page boundaries yet.
* Includes a complete I2C transaction.
*/
int8_t Storage::i2c_read(uint16_t pos, uint8_t len, uint8_t *data)
{
uint8_t addr_buf[2];
addr_buf[0] = pos >> 8;
addr_buf[1] = pos & 0xff;
i2c_start_write();
i2c_send(2, addr_buf);
i2c_start_read();
i2c_receive(len, data);
i2c_stop();
return 0; // TODO proper return code to indicate read/write errors
}
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