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Update code style 

Update indention to spaces
Fix comments
Add README.md and GPL-2 LICENSE files
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Olaf Rempel 1 month ago
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  1. +262
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      LICENSE
  2. +15
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      Makefile
  3. +96
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      README.md
  4. +365
    -322
      main.c

+ 262
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LICENSE View File

@@ -0,0 +1,262 @@
GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA

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END OF TERMS AND CONDITIONS

+ 15
- 4
Makefile View File

@@ -16,7 +16,9 @@ AVRDUDE_PROG := -c avr910 -b 115200 -P /dev/ttyUSB0
# ---------------------------------------------------------------------------

ifeq ($(MCU), atmega8)
# (8Mhz internal RC-Osz., 2.7V BOD)
# atmega8:
# Fuse L: 0x84 (8Mhz internal RC-Osz., 2.7V BOD)
# Fuse H: 0xda (512 words bootloader)
AVRDUDE_MCU=m8
AVRDUDE_FUSES=lfuse:w:0x84:m hfuse:w:0xda:m

@@ -24,7 +26,10 @@ BOOTLOADER_START=0x1C00
endif

ifeq ($(MCU), atmega88)
# (8Mhz internal RC-Osz., 2.7V BOD)
# atmega88:
# Fuse L: 0xc2 (8Mhz internal RC-Osz.)
# Fuse H: 0xdd (2.7V BOD)
# Fuse E: 0xfa (512 words bootloader)
AVRDUDE_MCU=m88
AVRDUDE_FUSES=lfuse:w:0xc2:m hfuse:w:0xdd:m efuse:w:0xfa:m

@@ -32,7 +37,10 @@ BOOTLOADER_START=0x1C00
endif

ifeq ($(MCU), atmega168)
# (8Mhz internal RC-Osz., 2.7V BOD)
# atmega168:
# Fuse L: 0xc2 (8Mhz internal RC-Osz.)
# Fuse H: 0xdd (2.7V BOD)
# Fuse E: 0xfa (512 words bootloader)
AVRDUDE_MCU=m168 -F
AVRDUDE_FUSES=lfuse:w:0xc2:m hfuse:w:0xdd:m efuse:w:0xfa:m

@@ -40,7 +48,10 @@ BOOTLOADER_START=0x3C00
endif

ifeq ($(MCU), atmega328p)
# (8Mhz internal RC-Osz., 2.7V BOD)
# atmega328p:
# Fuse L: 0xc2 (8Mhz internal RC-Osz.)
# Fuse H: 0xdc (512 words bootloader)
# Fuse E: 0xfd (2.7V BOD)
AVRDUDE_MCU=m328p -F
AVRDUDE_FUSES=lfuse:w:0xc2:m hfuse:w:0xdc:m efuse:w:0xfd:m


+ 96
- 0
README.md View File

@@ -0,0 +1,96 @@
# twiboot - a TWI / I2C bootloader for AVR MCUs ##
twiboot is a simple/small bootloader for AVR MCUs with integrated TWI peripheral written in C.
It was originally created to update I2C controlled BLMCs (Brushless Motor Controller) without an AVR ISP adapter.

twiboot acts as a slave device on a TWI/I2C bus and allows reading/writing of the internal flash memory.
As a compile time option twiboot also allows reading/writing of the whole internal EEPROM memory.
The bootloader is not able to update itself (only application flash memory region accessible).

Currently the following AVR MCUs are supported:

AVR MCU | Flash bytes used (.text + .data) | Bootloader region size
--- | --- | ---
atmega8 | 900 (0x384) | 512 words
atmega88 | 950 (0x3B6) | 512 words
atmega168 | 1002 (0x3EA) | 512 words
atmega328p | 1002 (0x3EA) | 512 words
(Compiled on Ubuntu 18.04 LTS (gcc 5.4.0 / avr-libc 2.0.0) with EEPROM and LED support)


## Operation ##
twiboot is installed in the bootloader memory region and executed directly after reset (BOOTRST fuse is programmed).

While running, twiboot configures the TWI peripheral as slave device and waits for valid protocol messages
directed to its address on the TWI/I2C bus. The slave address is configured during compile time of twiboot.
When receiving no messages for 1000ms after reset, the bootloader exits and executes the main application at address 0x0000.

A TWI/I2C master can use the protocol to
- abort the boot timeout
- query information about the device (bootloader version, AVR signature bytes, flash/eeprom size, flash page size)
- read internal flash / eeprom memory (byte wise)
- write the internal flash (page wise)
- write the internal eeprom (byte wise)
- exit the bootloader and start the application

As a compile time option twiboot can output its state with two LEDs.
One LED will flash with a frequency of 20Hz while twiboot is active (including boot wait time).
A second LED will flash when the bootloader is addressed on the TWI/I2C bus.


## Build and install twiboot ##
twiboot uses gcc, avr-libc and GNU Make for building, avrdude is used for flashing the MCU.
The build and install procedures are only tested under linux.

The selection of the target MCU and the programming interface can be found in the Makefile,
TWI/I2C slave address and optional components (EEPROM / LED support) are configured
in the main.c source.

To build twiboot for the selected target:
``` shell
$ make
```

To install (flash download) twiboot with avrdude on the target:
``` shell
$ make install
```

Set AVR fuses with avrdude on the target (internal RC-Osz, enable BOD, enable BOOTRST):
``` shell
$ make fuses
```


## TWI/I2C Protocol ##
A TWI/I2C master can use the following protocol for accessing the bootloader.

Function | TWI/I2C data | Comment
--- | --- | ---
Abort boot timeout | **SLA+W**, 0x00, **STO** |
Show bootloader version | **SLA+W**, 0x01, **SLA+R**, {16 bytes}, **STO** | ASCII, not null terminated
Start application | **SLA+W**, 0x01, 0x80, **STO** |
Read chip info | **SLA+W**, 0x02, 0x00, 0x00, 0x00, **SLA+R**, {8 bytes}, **STO** | 3byte signature, 1byte page size, 2byte flash size, 2byte eeprom size
Read 1+ flash bytes | **SLA+W**, 0x02, 0x01, addrh, addrl, **SLA+R**, {* bytes}, **STO** |
Read 1+ eeprom bytes | **SLA+W**, 0x02, 0x02, addrh, addrl, **SLA+R**, {* bytes}, **STO** |
Write one flash page | **SLA+W**, 0x02, 0x01, addrh, addrl, {* bytes}, **STO** | page size as indicated in chip info
Write 1+ eeprom bytes | **SLA+W**, 0x02, 0x02, addrh, addrl, {* bytes}, **STO** |

**SLA+R** means Start Condition, Slave Address, Read Access

**SLA+W** means Start Condition, Slave Address, Write Access

**STO** means Stop Condition

The multiboot_tool repository contains a simple linux application that uses
this protocol to access the bootloader over linux i2c device.


## Development ##
Issue reports, feature requests, patches or simply success stories are much appreciated.


## Roadmap ##
Some ideas that I want to investigate / implement in twiboot:
- [ ] do not use interrupts and remove vector table to save flash space
- [ ] find a way to not rely on TWI clock stretching during write access
- [ ] support AVR TINYs (USI peripheral, no bootloader fuse, no Read-While-Write flash)

+ 365
- 322
main.c View File

@@ -1,5 +1,5 @@
/***************************************************************************
* Copyright (C) 08/2010 by Olaf Rempel *
* Copyright (C) 11/2019 by Olaf Rempel *
* razzor@kopf-tisch.de *
* *
* This program is free software; you can redistribute it and/or modify *
@@ -21,64 +21,43 @@
#include <avr/boot.h>
#include <avr/pgmspace.h>

/*
* atmega8:
* Fuse H: 0xda (512 words bootloader)
* Fuse L: 0x84 (8Mhz internal RC-Osz., 2.7V BOD)
*
* atmega88:
* Fuse E: 0xfa (512 words bootloader)
* Fuse H: 0xdd (2.7V BOD)
* Fuse L: 0xc2 (8Mhz internal RC-Osz.)
*
* atmega168:
* Fuse E: 0xfa (512 words bootloader)
* Fuse H: 0xdd (2.7V BOD)
* Fuse L: 0xc2 (8Mhz internal RC-Osz.)
*
* atmega328p:
* Fuse E: 0xfd (2.7V BOD)
* Fuse H: 0xdc (512 words bootloader)
* Fuse L: 0xc2 (8Mhz internal RC-Osz.)
*/

#if defined (__AVR_ATmega8__)
#define VERSION_STRING "TWIBOOT m8v2.1"
#define SIGNATURE_BYTES 0x1E, 0x93, 0x07
#define VERSION_STRING "TWIBOOT m8v2.1"
#define SIGNATURE_BYTES 0x1E, 0x93, 0x07

#elif defined (__AVR_ATmega88__)
#define VERSION_STRING "TWIBOOT m88v2.1"
#define SIGNATURE_BYTES 0x1E, 0x93, 0x0A
#define VERSION_STRING "TWIBOOT m88v2.1"
#define SIGNATURE_BYTES 0x1E, 0x93, 0x0A

#elif defined (__AVR_ATmega168__)
#define VERSION_STRING "TWIBOOT m168v2.1"
#define SIGNATURE_BYTES 0x1E, 0x94, 0x06
#define VERSION_STRING "TWIBOOT m168v2.1"
#define SIGNATURE_BYTES 0x1E, 0x94, 0x06

#elif defined (__AVR_ATmega328P__)
#define VERSION_STRING "TWIBOOTm328pv2.1"
#define SIGNATURE_BYTES 0x1E, 0x95, 0x0F
#define VERSION_STRING "TWIBOOTm328pv2.1"
#define SIGNATURE_BYTES 0x1E, 0x95, 0x0F

#else
#error MCU not supported
#endif

#define EEPROM_SUPPORT 1
#define LED_SUPPORT 1
#define EEPROM_SUPPORT 1
#define LED_SUPPORT 1

/* 25ms @8MHz */
#define TIMER_RELOAD (0xFF - 195)
#define TIMER_RELOAD (0xFF - 195)

/* 40 * 25ms */
#define TIMEOUT 40
#define TIMEOUT 40

#if LED_SUPPORT
#define LED_INIT() DDRB = ((1<<PORTB4) | (1<<PORTB5))
#define LED_RT_ON() PORTB |= (1<<PORTB4)
#define LED_RT_OFF() PORTB &= ~(1<<PORTB4)
#define LED_GN_ON() PORTB |= (1<<PORTB5)
#define LED_GN_OFF() PORTB &= ~(1<<PORTB5)
#define LED_GN_TOGGLE() PORTB ^= (1<<PORTB5)
#define LED_OFF() PORTB = 0x00
#define LED_INIT() DDRB = ((1<<PORTB4) | (1<<PORTB5))
#define LED_RT_ON() PORTB |= (1<<PORTB4)
#define LED_RT_OFF() PORTB &= ~(1<<PORTB4)
#define LED_GN_ON() PORTB |= (1<<PORTB5)
#define LED_GN_OFF() PORTB &= ~(1<<PORTB5)
#define LED_GN_TOGGLE() PORTB ^= (1<<PORTB5)
#define LED_OFF() PORTB = 0x00
#else
#define LED_INIT()
#define LED_RT_ON()
@@ -90,43 +69,43 @@
#endif

#ifndef TWI_ADDRESS
#define TWI_ADDRESS 0x29
#define TWI_ADDRESS 0x29
#endif

/* SLA+R */
#define CMD_WAIT 0x00
#define CMD_READ_VERSION 0x01
#define CMD_READ_MEMORY 0x02
#define CMD_WAIT 0x00
#define CMD_READ_VERSION 0x01
#define CMD_READ_MEMORY 0x02
/* internal mappings */
#define CMD_READ_CHIPINFO (0x10 | CMD_READ_MEMORY)
#define CMD_READ_FLASH (0x20 | CMD_READ_MEMORY)
#define CMD_READ_EEPROM (0x30 | CMD_READ_MEMORY)
#define CMD_READ_PARAMETERS (0x40 | CMD_READ_MEMORY) /* only in APP */
#define CMD_READ_CHIPINFO (0x10 | CMD_READ_MEMORY)
#define CMD_READ_FLASH (0x20 | CMD_READ_MEMORY)
#define CMD_READ_EEPROM (0x30 | CMD_READ_MEMORY)
#define CMD_READ_PARAMETERS (0x40 | CMD_READ_MEMORY) /* only in APP */

/* SLA+W */
#define CMD_SWITCH_APPLICATION CMD_READ_VERSION
#define CMD_WRITE_MEMORY CMD_READ_MEMORY
#define CMD_SWITCH_APPLICATION CMD_READ_VERSION
#define CMD_WRITE_MEMORY CMD_READ_MEMORY
/* internal mappings */
#define CMD_BOOT_BOOTLOADER (0x10 | CMD_SWITCH_APPLICATION) /* only in APP */
#define CMD_BOOT_APPLICATION (0x20 | CMD_SWITCH_APPLICATION)
#define CMD_WRITE_CHIPINFO (0x10 | CMD_WRITE_MEMORY) /* invalid */
#define CMD_WRITE_FLASH (0x20 | CMD_WRITE_MEMORY)
#define CMD_WRITE_EEPROM (0x30 | CMD_WRITE_MEMORY)
#define CMD_WRITE_PARAMETERS (0x40 | CMD_WRITE_MEMORY) /* only in APP */
#define CMD_BOOT_BOOTLOADER (0x10 | CMD_SWITCH_APPLICATION) /* only in APP */
#define CMD_BOOT_APPLICATION (0x20 | CMD_SWITCH_APPLICATION)
#define CMD_WRITE_CHIPINFO (0x10 | CMD_WRITE_MEMORY) /* invalid */
#define CMD_WRITE_FLASH (0x20 | CMD_WRITE_MEMORY)
#define CMD_WRITE_EEPROM (0x30 | CMD_WRITE_MEMORY)
#define CMD_WRITE_PARAMETERS (0x40 | CMD_WRITE_MEMORY) /* only in APP */

/* CMD_SWITCH_APPLICATION parameter */
#define BOOTTYPE_BOOTLOADER 0x00 /* only in APP */
#define BOOTTYPE_APPLICATION 0x80
#define BOOTTYPE_BOOTLOADER 0x00 /* only in APP */
#define BOOTTYPE_APPLICATION 0x80

/* CMD_{READ|WRITE}_* parameter */
#define MEMTYPE_CHIPINFO 0x00
#define MEMTYPE_FLASH 0x01
#define MEMTYPE_EEPROM 0x02
#define MEMTYPE_PARAMETERS 0x03 /* only in APP */
#define MEMTYPE_CHIPINFO 0x00
#define MEMTYPE_FLASH 0x01
#define MEMTYPE_EEPROM 0x02
#define MEMTYPE_PARAMETERS 0x03 /* only in APP */

/*
* LED_GN blinks with 20Hz (while bootloader is running)
* LED_RT blinks on TWI activity
* LED_GN flashes with 20Hz (while bootloader is running)
* LED_RT flashes on TWI activity
*
* bootloader twi-protocol:
* - abort boot timeout:
@@ -139,7 +118,7 @@
* SLA+W, 0x01, 0x80, STO
*
* - read chip info: 3byte signature, 1byte page size, 2byte flash size, 2byte eeprom size
* SLA+W, 0x02, 0x00, 0x00, 0x00, SLA+R, {4 bytes}, STO
* SLA+W, 0x02, 0x00, 0x00, 0x00, SLA+R, {8 bytes}, STO
*
* - read one (or more) flash bytes
* SLA+W, 0x02, 0x01, addrh, addrl, SLA+R, {* bytes}, STO
@@ -147,8 +126,8 @@
* - read one (or more) eeprom bytes
* SLA+W, 0x02, 0x02, addrh, addrl, SLA+R, {* bytes}, STO
*
* - write one flash page (64bytes on mega8)
* SLA+W, 0x02, 0x01, addrh, addrl, {64 bytes}, STO
* - write one flash page
* SLA+W, 0x02, 0x01, addrh, addrl, {* bytes}, STO
*
* - write one (or more) eeprom bytes
* SLA+W, 0x02, 0x02, addrh, addrl, {* bytes}, STO
@@ -156,17 +135,17 @@

const static uint8_t info[16] = VERSION_STRING;
const static uint8_t chipinfo[8] = {
SIGNATURE_BYTES,
SIGNATURE_BYTES,
SPM_PAGESIZE,

SPM_PAGESIZE,
(BOOTLOADER_START >> 8) & 0xFF,
BOOTLOADER_START & 0xFF,

(BOOTLOADER_START >> 8) & 0xFF,
BOOTLOADER_START & 0xFF,
#if (EEPROM_SUPPORT)
((E2END +1) >> 8 & 0xFF),
(E2END +1) & 0xFF
((E2END +1) >> 8 & 0xFF),
(E2END +1) & 0xFF
#else
0x00, 0x00
0x00, 0x00
#endif
};

@@ -178,305 +157,369 @@ volatile static uint8_t cmd = CMD_WAIT;
static uint8_t buf[SPM_PAGESIZE];
static uint16_t addr;

/* *************************************************************************
* write_flash_page
* ************************************************************************* */
static void write_flash_page(void)
{
uint16_t pagestart = addr;
uint8_t size = SPM_PAGESIZE;
uint8_t *p = buf;
uint16_t pagestart = addr;
uint8_t size = SPM_PAGESIZE;
uint8_t *p = buf;

if (pagestart >= BOOTLOADER_START)
return;
if (pagestart >= BOOTLOADER_START)
{
return;
}

boot_page_erase(pagestart);
boot_spm_busy_wait();
boot_page_erase(pagestart);
boot_spm_busy_wait();

do {
uint16_t data = *p++;
data |= *p++ << 8;
boot_page_fill(addr, data);
do {
uint16_t data = *p++;
data |= *p++ << 8;
boot_page_fill(addr, data);

addr += 2;
size -= 2;
} while (size);
addr += 2;
size -= 2;
} while (size);

boot_page_write(pagestart);
boot_spm_busy_wait();
boot_rww_enable();
} /* write_flash_page */

boot_page_write(pagestart);
boot_spm_busy_wait();
boot_rww_enable();
}

#if (EEPROM_SUPPORT)
/* *************************************************************************
* read_eeprom_byte
* ************************************************************************* */
static uint8_t read_eeprom_byte(void)
{
EEARL = addr;
EEARH = (addr >> 8);
EECR |= (1<<EERE);
addr++;
return EEDR;
}
EEARL = addr;
EEARH = (addr >> 8);
EECR |= (1<<EERE);
addr++;

return EEDR;
} /* read_eeprom_byte */


/* *************************************************************************
* write_eeprom_byte
* ************************************************************************* */
static void write_eeprom_byte(uint8_t val)
{
EEARL = addr;
EEARH = (addr >> 8);
EEDR = val;
addr++;
EEARL = addr;
EEARH = (addr >> 8);
EEDR = val;
addr++;

#if defined (__AVR_ATmega8__)
EECR |= (1<<EEMWE);
EECR |= (1<<EEWE);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || defined (__AVR_ATmega328P__)
EECR |= (1<<EEMPE);
EECR |= (1<<EEPE);
EECR |= (1<<EEMWE);
EECR |= (1<<EEWE);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || \
defined (__AVR_ATmega328P__)
EECR |= (1<<EEMPE);
EECR |= (1<<EEPE);
#endif
eeprom_busy_wait();
}

eeprom_busy_wait();
} /* write_eeprom_byte */
#endif /* EEPROM_SUPPORT */


/* *************************************************************************
* TWI_vect
* ************************************************************************* */
ISR(TWI_vect)
{
static uint8_t bcnt;
uint8_t data;
uint8_t ack = (1<<TWEA);

switch (TWSR & 0xF8) {
/* SLA+W received, ACK returned -> receive data and ACK */
case 0x60:
bcnt = 0;
LED_RT_ON();
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* prev. SLA+W, data received, ACK returned -> receive data and ACK */
case 0x80:
data = TWDR;
switch (bcnt) {
case 0:
switch (data) {
case CMD_SWITCH_APPLICATION:
case CMD_WRITE_MEMORY:
bcnt++;
/* no break */

case CMD_WAIT:
/* abort countdown */
boot_timeout = 0;
break;

default:
/* boot app now */
cmd = CMD_BOOT_APPLICATION;
ack = (0<<TWEA);
break;
}
cmd = data;
break;

case 1:
switch (cmd) {
case CMD_SWITCH_APPLICATION:
if (data == BOOTTYPE_APPLICATION) {
cmd = CMD_BOOT_APPLICATION;
}
ack = (0<<TWEA);
break;

case CMD_WRITE_MEMORY:
bcnt++;
if (data == MEMTYPE_CHIPINFO) {
cmd = CMD_WRITE_CHIPINFO;

} else if (data == MEMTYPE_FLASH) {
cmd = CMD_WRITE_FLASH;
static uint8_t bcnt;
uint8_t data;
uint8_t ack = (1<<TWEA);

switch (TWSR & 0xF8)
{
/* SLA+W received, ACK returned -> receive data and ACK */
case 0x60:
bcnt = 0;
LED_RT_ON();
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* prev. SLA+W, data received, ACK returned -> receive data and ACK */
case 0x80:
data = TWDR;

switch (bcnt)
{
case 0:
switch (data)
{
case CMD_SWITCH_APPLICATION:
case CMD_WRITE_MEMORY:
bcnt++;
/* no break */

case CMD_WAIT:
/* abort countdown */
boot_timeout = 0;
break;

default:
/* boot app now */
cmd = CMD_BOOT_APPLICATION;
ack = (0<<TWEA);
break;
}

cmd = data;
break;

case 1:
switch (cmd)
{
case CMD_SWITCH_APPLICATION:
if (data == BOOTTYPE_APPLICATION)
{
cmd = CMD_BOOT_APPLICATION;
}

ack = (0<<TWEA);
break;

case CMD_WRITE_MEMORY:
bcnt++;
if (data == MEMTYPE_CHIPINFO)
{
cmd = CMD_WRITE_CHIPINFO;
}
else if (data == MEMTYPE_FLASH)
{
cmd = CMD_WRITE_FLASH;
}
#if (EEPROM_SUPPORT)
} else if (data == MEMTYPE_EEPROM) {
cmd = CMD_WRITE_EEPROM;
#endif
} else {
ack = (0<<TWEA);
}
break;

default:
ack = (0<<TWEA);
break;
}
break;

case 2:
case 3:
addr <<= 8;
addr |= data;
bcnt++;
break;

default:
switch (cmd) {
case CMD_WRITE_FLASH:
buf[bcnt -4] = data;
if (bcnt < sizeof(buf) +3) {
bcnt++;
} else {
write_flash_page();
ack = (0<<TWEA);
}
break;
#if (EEPROM_SUPPORT)
case CMD_WRITE_EEPROM:
write_eeprom_byte(data);
bcnt++;
break;
#endif
default:
ack = (0<<TWEA);
break;
}
break;
}

if (ack == 0x00)
bcnt = 0;

TWCR |= (1<<TWINT) | ack;
break;

/* SLA+R received, ACK returned -> send data */
case 0xA8:
bcnt = 0;
LED_RT_ON();

/* prev. SLA+R, data sent, ACK returned -> send data */
case 0xB8:
switch (cmd) {
case CMD_READ_VERSION:
data = info[bcnt++];
bcnt %= sizeof(info);
break;

case CMD_READ_CHIPINFO:
data = chipinfo[bcnt++];
bcnt %= sizeof(chipinfo);
break;

case CMD_READ_FLASH:
data = pgm_read_byte_near(addr++);
break;
else if (data == MEMTYPE_EEPROM)
{
cmd = CMD_WRITE_EEPROM;
}
#endif /* (EEPROM_SUPPORT) */
else
{
ack = (0<<TWEA);
}
break;

default:
ack = (0<<TWEA);
break;
}
break;

case 2:
case 3:
addr <<= 8;
addr |= data;
bcnt++;
break;

default:
switch (cmd)
{
case CMD_WRITE_FLASH:
buf[bcnt -4] = data;
if (bcnt < sizeof(buf) +3)
{
bcnt++;
}
else
{
write_flash_page();
ack = (0<<TWEA);
}
break;

#if (EEPROM_SUPPORT)
case CMD_READ_EEPROM:
data = read_eeprom_byte();
break;
#endif
default:
data = 0xFF;
break;
}

TWDR = data;
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* STOP or repeated START */
case 0xA0:
/* data sent, NACK returned */
case 0xC0:
LED_RT_OFF();
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* illegal state -> reset hardware */
case 0xF8:
TWCR |= (1<<TWINT) | (1<<TWSTO) | (1<<TWEA);
break;
}
}
case CMD_WRITE_EEPROM:
write_eeprom_byte(data);
bcnt++;
break;
#endif /* (EEPROM_SUPPORT) */

default:
ack = (0<<TWEA);
break;
}
break;
}

if (ack == 0x00)
{
bcnt = 0;
}

TWCR |= (1<<TWINT) | ack;
break;

/* SLA+R received, ACK returned -> send data */
case 0xA8:
bcnt = 0;
LED_RT_ON();

/* prev. SLA+R, data sent, ACK returned -> send data */
case 0xB8:
switch (cmd)
{
case CMD_READ_VERSION:
data = info[bcnt++];
bcnt %= sizeof(info);
break;

case CMD_READ_CHIPINFO:
data = chipinfo[bcnt++];
bcnt %= sizeof(chipinfo);
break;

case CMD_READ_FLASH:
data = pgm_read_byte_near(addr++);
break;

#if (EEPROM_SUPPORT)
case CMD_READ_EEPROM:
data = read_eeprom_byte();
break;
#endif /* (EEPROM_SUPPORT) */

default:
data = 0xFF;
break;
}

TWDR = data;
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* STOP or repeated START -> IDLE */
case 0xA0:
/* prev. SLA+R, data sent, NACK returned -> IDLE */
case 0xC0:
LED_RT_OFF();
TWCR |= (1<<TWINT) | (1<<TWEA);
break;

/* illegal state -> reset hardware */
case 0xF8:
TWCR |= (1<<TWINT) | (1<<TWSTO) | (1<<TWEA);
break;
}
} /* TWI_vect */


/* *************************************************************************
* TIMER0_OVF_vect
* ************************************************************************* */
ISR(TIMER0_OVF_vect)
{
/* restart timer */
TCNT0 = TIMER_RELOAD;
/* restart timer */
TCNT0 = TIMER_RELOAD;

/* blink LED while running */
LED_GN_TOGGLE();
/* blink LED while running */
LED_GN_TOGGLE();

/* count down for app-boot */
if (boot_timeout > 1)
boot_timeout--;
/* count down for app-boot */
if (boot_timeout > 1)
{
boot_timeout--;
}
else if (boot_timeout == 1)
{
/* trigger app-boot */
cmd = CMD_BOOT_APPLICATION;
}
} /* TIMER0_OVF_vect */

/* trigger app-boot */
else if (boot_timeout == 1)
cmd = CMD_BOOT_APPLICATION;
}

static void (*jump_to_app)(void) __attribute__ ((noreturn)) = 0x0000;

/*
* For newer devices (mega88) the watchdog timer remains active even after a
* For newer devices the watchdog timer remains active even after a
* system reset. So disable it as soon as possible.
* automagically called on startup
*/
#if defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || defined (__AVR_ATmega328P__)
#if defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || \
defined (__AVR_ATmega328P__)
/* *************************************************************************
* disable_wdt_timer
* ************************************************************************* */
void disable_wdt_timer(void) __attribute__((naked, section(".init3")));
void disable_wdt_timer(void)
{
MCUSR = 0;
WDTCSR = (1<<WDCE) | (1<<WDE);
WDTCSR = (0<<WDE);
}
MCUSR = 0;
WDTCSR = (1<<WDCE) | (1<<WDE);
WDTCSR = (0<<WDE);
} /* disable_wdt_timer */
#endif


/* *************************************************************************
* main
* ************************************************************************* */
int main(void) __attribute__ ((noreturn));
int main(void)
{
LED_INIT();
LED_GN_ON();
LED_INIT();
LED_GN_ON();

/* move interrupt-vectors to bootloader */
/* timer0: running with F_CPU/1024, OVF interrupt */
/* move interrupt-vectors to bootloader */
/* timer0: running with F_CPU/1024, OVF interrupt */
#if defined (__AVR_ATmega8__)
GICR = (1<<IVCE);
GICR = (1<<IVSEL);

TCCR0 = (1<<CS02) | (1<<CS00);
TIMSK = (1<<TOIE0);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || defined (__AVR_ATmega328P__)
MCUCR = (1<<IVCE);
MCUCR = (1<<IVSEL);

TCCR0B = (1<<CS02) | (1<<CS00);
TIMSK0 = (1<<TOIE0);
GICR = (1<<IVCE);
GICR = (1<<IVSEL);

TCCR0 = (1<<CS02) | (1<<CS00);
TIMSK = (1<<TOIE0);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || \
defined (__AVR_ATmega328P__)
MCUCR = (1<<IVCE);
MCUCR = (1<<IVSEL);

TCCR0B = (1<<CS02) | (1<<CS00);
TIMSK0 = (1<<TOIE0);
#endif

/* TWI init: set address, auto ACKs with interrupts */
TWAR = (TWI_ADDRESS<<1);
TWCR = (1<<TWEA) | (1<<TWEN) | (1<<TWIE);
/* TWI init: set address, auto ACKs with interrupts */
TWAR = (TWI_ADDRESS<<1);
TWCR = (1<<TWEA) | (1<<TWEN) | (1<<TWIE);

sei();
while (cmd != CMD_BOOT_APPLICATION);
cli();
sei();
while (cmd != CMD_BOOT_APPLICATION);
cli();

/* Disable TWI but keep address! */
TWCR = 0x00;
/* Disable TWI but keep address! */
TWCR = 0x00;

/* disable timer0 */
/* move interrupt vectors back to application */
/* disable timer0 */
/* move interrupt vectors back to application */
#if defined (__AVR_ATmega8__)
TCCR0 = 0x00;
TIMSK = 0x00;

GICR = (1<<IVCE);
GICR = (0<<IVSEL);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || defined (__AVR_ATmega328P__)
TIMSK0 = 0x00;
TCCR0B = 0x00;

MCUCR = (1<<IVCE);
MCUCR = (0<<IVSEL);
TCCR0 = 0x00;
TIMSK = 0x00;

GICR = (1<<IVCE);
GICR = (0<<IVSEL);
#elif defined (__AVR_ATmega88__) || defined (__AVR_ATmega168__) || \
defined (__AVR_ATmega328P__)
TIMSK0 = 0x00;
TCCR0B = 0x00;

MCUCR = (1<<IVCE);
MCUCR = (0<<IVSEL);
#endif

LED_OFF();
LED_OFF();

uint16_t wait = 0x0000;
do {
__asm volatile ("nop");
} while (--wait);
uint16_t wait = 0x0000;
do {
__asm volatile ("nop");
} while (--wait);

jump_to_app();
}
jump_to_app();
} /* main */

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