Two libraries are used to interface with the "write-to-flash" functionality the Optiboot bootloader has. Flash.h/cpp is a high-level library that makes it easy to store strings, variables, structs, etc. to the flash memory and easily retrieve them. optiboot.h/cpp is a low-level read/write library that does the actual reading and writing to flash. If your application needs more storage than the EEPROM can offer, Flash is the library for you. If you're very memory constrained and want to do the heavy lifting yourself, optiboot is the library for you. See the examples of how you can interface with these two libraries.
This is not the same library as the DxCore Flash.h
Dx-series and the tinyAVR/megaAVR 0/1/2-series parts have different versions of NVMCTRL; among other things, you need to both fill the page buffer and give the command to write it from within the bootloader section on tinyAVR/megaAVR - but on Dx-series parts, only the calls to SPM, and ST Z are protected, and there is no page buffer at all. The different hardware requirements, as well as the relative abundance of available flash in the bootloader section of the tinyAVR/megaAVR parts (they have 36 bytes left; on the Dx-series
I was rewriting ever larger chunks in assembly to get an extra 2-4 bytes so I could fit it into 512b) set the stage for drastically different implementations - and the two authors were unfamiliar with the other's work until after it was complete, and took radically different approaches to essentially every aspect of the design.
Class constructor for interfacing with the "write-to-flash" functionality. For arguments has to be present. A reference to the allocated flash space array, the size of the allocated space, a RAM buffer, and its size.
// Create object 'flash' with flash_space_array and ram_buffer
Flash flash(flash_space_array, sizeof(flash_space_array), ram_buffer, sizeof(ram_buffer));Operator overloaded object. This lets you use the object itself to access the RAM buffer.
uint8_t data = flash[0x00]; // Read data from address 0x00 in the buffer
flash[0x00] = data; // Write the contents of 'data' to address 0x00Checks if a bootloader that has "write-to-flash" functionality is present
bool valid_bootloader = flash.check_writable();bool valid bootloader present
Clears the RAM buffer. Sets all values to 0x00 if no parameter is present
flash.clear_buffer(); // Write all zeros to the RAM buffer
flash.clear:buffer(0xff); // Write all 0xff's to the RAM buffervoid
Alternative to flash[]. Reads a byte from the RAM buffer.
uint8_t data = flash.read_buffer(0x00); // Read data from place 0x00 in the buffer
uint8_t data = flash.read_buffer(0x40); // Read data from place 0x40uint8_t data in buffer place N
Alternative to flash[]. Writes a byte to the RAM buffer
flash.write_buffer(0x00, 'H'); // Write character 'H' to buffer place 0x00void
Returns the size of the allocated RAM buffer in bytes
uint16_t allocated_buffer = flash.buffer_size();uint16_t buffer size in bytes
Writes the RAM buffer to flash
flash.write_page(1); // Write buffer to flash page 1void
Fetches a flash page and stores it in the RAM buffer
flash.fetch_page(1); // Fetch flash page 1void
Fetches a given amount of data from flash. Note that the start and stop address is relative to the start of the flash space array. This means that the span can't be larger than the size of the RAM buffer.
flash.fetch_data(128, 192); // Read 64 bytes of data from beginning of flash page one (128 bytes flash page size)void
Write any data type or object to flash
float f = 123.456f;
char text[13] = "Hello World!";
flash.put(0x00, f); // Store float value to flash, starting from address 0
flash.put(sizeof(float), text); // Store text after the float variableRead any data type or object from flash
float f;
char text[13];
flash.get(0x00, f); // Fetch float variable from flash address 0 and store it to variable f
flash.get(sizeof(float), text); // Fetch text after the float variableChecks if a bootloader that has "write-to-flash" functionality is present
bool valid_bootloader = optiboot_check_writable();bool valid bootloader present
Reads data from the flash memory into a buffer
optiboot_read(flash_space_array, ram_buffer, page_number, page_start_address, page_stop_address);void
Reads an entire flash page into a buffer
optiboot_readPage(flash_space_array, ram_buffer, page_number);void
Writes data to a flash page
optiboot_writePage(flash_space_array, ram_buffer, page_number);void