{"id":10144,"date":"2013-06-14T11:37:17","date_gmt":"2013-06-14T15:37:17","guid":{"rendered":"http:\/\/engineersgarag-main\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/"},"modified":"2023-05-24T12:01:49","modified_gmt":"2023-05-24T16:01:49","slug":"how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46","status":"publish","type":"post","link":"https:\/\/www.engineersgarage.com\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/","title":{"rendered":"How To Write a Simple Bootloader For AVR In C language- (Part 35\/46)"},"content":{"rendered":"

 <\/p>\n

The AVR flash memory is divided into two sections namely the application section and the Boot-Loader section (BLS). In case of the ATMEGA16 it has 16 KB of flash memory of which the 15KB is application section and the remaining 1KB is BLS. The memory architecture of the ATMEGA16 is shown in the following figure;<\/span><\/span><\/span><\/p>\n

\"Flash<\/span><\/span><\/p>\n

Fig. 2: Flash Memory Architecture of ATMEGA16<\/em><\/span><\/span><\/p>\n

The code for both the BLS and application section can be written as normally does and there is no much difference. The only thing to be careful about is the size of the code binary. It should not be more than 1KB, otherwise it won\u2019t be able to code programmed into the BLS. The <\/span><\/span><\/span>project<\/span><\/span> on AVR BLS coding discusses how to program a simple code into the BLS of ATMEGA16 microcontroller with the help of AVR studio as IDE, USBasp as the programmer and AVR-Burnomat as the burner software.<\/span><\/span><\/span><\/p>\n

In this particular project the Boot-Loader is coded to perform <\/span><\/span><\/span>UART<\/span><\/span><\/a> initialization along with a simple <\/span><\/span>LED<\/span><\/span> pin initialization and also an external hardware initialization of the 4 bit <\/span><\/span>LCD<\/span><\/span>. Hence the application codes does not require those codes in them, still they works because before executing the application codes the initialization functions will be executed by the Boot-Loader.<\/span><\/span><\/span><\/p>\n

The BLS code has the initialization functions which should not be there in the application codes. The initialization functions used in the Boot-Loader code for this project are given below;<\/span><\/span><\/span><\/span><\/p>\n

\n\n\n\n\n\n\n
\n

Function<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

Description<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n<\/tr>\n

\n

void lcd_init ( void )<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Initialize the LCD in 4 bit mode<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

void usart_init ( void )<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Initialize the usart in 9600 baud rate with transmission and reception enabled<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

DDRD |= 0x80; <\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Initialization of the LED pin as output<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Fig.3 :Initialization functions used Boot-Loader code of AVR<\/em><\/p>\n<\/div>\n

Any application code can directly use the following function calls to access the USART, LCD and LED without their initializing functions anywhere in their code.<\/span><\/span><\/span><\/span><\/p>\n

\n\n\n\n\n\n\n\n\n
\n

Function<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

Description<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n<\/tr>\n

\n

lcd_clear ()<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Clear the LCD<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

lcd_string ()<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Display a string in the LCD<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

usart_send_string ()<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Send a string via usart<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

PORTD &= 0x7F;<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Turn ON the LED<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

PORTD |= 0x80;<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Turn OFF the LED<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 Fig. 4: Function calls used by application code to access peripherals in AVR<\/em><\/span><\/span><\/p>\n<\/div>\n

The hardware initialization before executing the application code is explained in detail in a <\/span><\/span><\/span>project<\/span><\/span> <\/span><\/span>on Initializing hardware from AVR BLS.<\/span><\/span><\/span><\/p>\n

The major function of the Boot-Loader is load a code binary form storage medium or which can be received through the external communication with other devices to the flash memory. The SPM feature available for the code executing from the BLS helps in loading an application code binary to the flash memory. The task of writing the BLS code with SPM has been made simple by the APIs available in the header file <avr\/boot.h>. The following are the important APIs available in the header file which helps in the SPM.<\/span><\/span><\/span><\/span><\/p>\n\n\n\n\n\n\n
\n

FUNCTION<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

DESCRIPTION<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

PARAMETER<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n<\/tr>\n

\n

boot_page_erase (address)<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Erase the flash page that is referred by address<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

A byte address in flash<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

boot_page_fill             (address, data)    <\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Fill the Boot-Loader temporary page buffer for flash address with data word<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

The address is a byte address. The data is a word<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n

\n

boot_page_write (address)<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Write the Boot-Loader temporary page buffer to flash page that contains address<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

Byte address in flash<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Fig. 5: <\/span>Important APIs in AVR <\/em><\/span><\/span><\/p>\n

The steps required to do the SPM on the application flash memory is explained in a <\/span><\/span><\/span>project<\/span><\/span> on using SPM in AVR flash to flash programming.<\/span><\/span><\/span><\/p>\n

In this particular project the Boot-Loader is coded in such a way that it will try to load any application code binary which has been loaded into the built-in internal EEPROM of the AVR microcontroller. The APIs available in the <avr\/eeprom.h> is used to read the data bytes from the EEPROM and with the help of APIs from the <avr\/boot.h> the data bytes are stored into a temporary buffer and then flashed into the application section of the flash memory.<\/span><\/span><\/span><\/span><\/p>\n

The API provided by the <avr\/eeprom.h> to read the data bytes from the built-in EEPROM of the AVR microcontroller is;<\/span><\/span><\/span><\/span><\/p>\n

uint8_t eeprom_read_byte (const uint8_t *p)<\/span><\/i><\/b><\/span><\/span><\/span><\/i><\/b><\/p>\n

 <\/span><\/span><\/span><\/p>\n\n\n\n\n
\n

FUNCTION<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

DESCRIPTION<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n

\n

PARAMETER<\/span><\/b><\/span><\/span><\/span><\/b><\/p>\n<\/td>\n<\/tr>\n

\n

uint8_t eeprom_read_byte (const uint8_t *p)<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

The function returns one data byte which is stored in the EEPROM address referred by the pointer p<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n

\n

The pointer refers to the EEPROM address from which the data byte need to be read<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Fig. 6: <\/span>API <avr\/eeprom.h> to read data bytes from in-built EEPROM of AVR microcontroller <\/em><\/span><\/span><\/p>\n

With the help of the above discussed APIs from both <avr\/boot.h> and <avr\/eeprom.h> one can use the SPM feature of the AVR microcontroller to write a Boot-Loader code which can load an application which has been programmed into the built-in EEPROM of the AVR microcontroller. For that one should follow the steps mentioned below which are explained in a <\/span><\/span><\/span>project<\/span><\/span> on using SPM in AVR EEPROM to flash programming.<\/span><\/span><\/span><\/p>\n

{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}\u00b7         <\/span><\/span>{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}Step: 1 Erase the flash page which is about to write into<\/span><\/span><\/span><\/span><\/p>\n

{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}\u00b7         <\/span><\/span>{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}Step: 2 Store the code binary which are read from the EEPROM into a temporary buffer before write into a flash page<\/span><\/span><\/span><\/span><\/p>\n

{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}\u00b7         <\/span><\/span>{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}{C}Step: 3 Program the filled temporary buffer into the already erased flash page<\/span><\/span><\/span><\/span><\/p>\n

After performing the above three steps the Boot-Loader can then make a jump using the statement <\/span><\/span><\/span><\/span><\/p>\n

asm ( “jmp 0x0000” );<\/span><\/i><\/b><\/span><\/span><\/span><\/i><\/b><\/p>\n

to the application code section and let the newly programmed application to execute.<\/span><\/span><\/span><\/span><\/p>\n

 <\/span><\/span><\/span><\/p>\n

Flash the Boot-Loader code to the BLS first any small sized application code to the EEPROM memory using the steps explained in the previous project on <\/span><\/span><\/span>LED blinking from BLS of AVR<\/span><\/span><\/span>. Once the EEPROM programming has completed and when the controller resets the Boot-Loader will start executing. Once can observe that it is performing the initialization functions and is loading the application from the built-in EEPROM.<\/span><\/span><\/span><\/p>\n

\"Burning<\/p>\n

Fig. 7: Burning BLS code into BLS of AVR circuit on breadboard<\/em><\/span><\/span><\/p>\n

 <\/p>\n

\"How<\/p>\n

 <\/p>\n

\"LCD<\/p>\n

Fig. 9: LCD Display initialized by BLS code in AVR setup on breadboard<\/em><\/span><\/span><\/p>\n

 <\/p>\n

\"How<\/p>\n

Fig. 10: USART initialized at 9600 baud rate by BLS of AVR setup on breadboard<\/em><\/span><\/span><\/p>\n

 <\/p>\n

\"How<\/p>\n

\n
\n
<\/div>\n

<\/div>\n<\/div>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

The Boot-Loader is a code which executes when a microcontroller is powered ON or reset. It basically sets an environment for the application code to execute. It is the Boot-Loader that sets the hardware and loads the application code from any storage medium or received through external communication and let the application to execute. Thus a Boot-Loader has to perform the following basic function : Initialize the controller peripherals, Initialize the devices in the board, Allow an option for the user to select from the available applications to load, Load the selected application, Let the application code to execute. Apart from the above mentioned functions some Boot-Loaders can perform many other functions and there are Boot-Loaders which don\u2019t perform all these functions like provide option to select the required application etc. The Boot-Loader codes in microcontrollers are actually very small and simple compared to the Boot-Loaders in advanced devices like PC. In most of the microcontroller the functionality of a Boot-Loader is limited only to set the initial clock and other settings for the microcontroller, load an application binary from the serial port etc. <\/p>\n","protected":false},"author":3,"featured_media":15858,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[4043,13],"tags":[218,457,1187],"class_list":{"2":"type-post","12":"entry","13":"has-post-thumbnail"},"acf":[],"yoast_head":"\nHow To Write a Simple Bootloader For AVR In C language- (Part 35\/46)<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.engineersgarage.com\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How To Write a Simple Bootloader For AVR In C language- (Part 35\/46)\" \/>\n<meta property=\"og:description\" content=\"The Boot-Loader is a code which executes when a microcontroller is powered ON or reset. 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Simple Bootloader For AVR In C language- (Part 35\/46)","og_description":"The Boot-Loader is a code which executes when a microcontroller is powered ON or reset. It basically sets an environment for the application code to execute. It is the Boot-Loader that sets the hardware and loads the application code from any storage medium or received through external communication and let the application to execute. Thus a Boot-Loader has to perform the following basic function : Initialize the controller peripherals, Initialize the devices in the board, Allow an option for the user to select from the available applications to load, Load the selected application, Let the application code to execute. Apart from the above mentioned functions some Boot-Loaders can perform many other functions and there are Boot-Loaders which don\u2019t perform all these functions like provide option to select the required application etc. The Boot-Loader codes in microcontrollers are actually very small and simple compared to the Boot-Loaders in advanced devices like PC. In most of the microcontroller the functionality of a Boot-Loader is limited only to set the initial clock and other settings for the microcontroller, load an application binary from the serial port etc. ","og_url":"https:\/\/www.engineersgarage.com\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/","og_site_name":"Engineers Garage","article_publisher":"https:\/\/www.facebook.com\/engineersgarage","og_image":[{"width":640,"height":480,"url":"https:\/\/www.engineersgarage.com\/wp-content\/uploads\/2019\/07\/Wrting-Simple-Boot-Loader-code-for-AVR-microcontroller-in-C-to-Initialize-peripherals-circuit-set-up-on-breadboard.jpg","type":"image\/jpeg"}],"author":"Ashutosh Bhatt","twitter_card":"summary_large_image","twitter_creator":"@EngineersGarage","twitter_site":"@EngineersGarage","twitter_misc":{"Written by":"Ashutosh Bhatt","Est. reading time":"6 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.engineersgarage.com\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/#article","isPartOf":{"@id":"https:\/\/www.engineersgarage.com\/how-to-write-a-simple-bootloader-for-avr-in-c-language-part-35-46\/"},"author":{"name":"Ashutosh Bhatt","@id":"https:\/\/www.engineersgarage.com\/#\/schema\/person\/4e6dc417fdf33f6ce27c9ce2f9fd08d3"},"headline":"How To Write a Simple Bootloader For AVR In C language- (Part 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