Overview

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Library to handle hexadecimal record files

• Free software: BSD 2-Clause License

Introduction

The purpose of this library is to provide simple but useful methods to load, edit, and save hexadecimal record files.

In the field of embedded systems, hexadecimal record files are the most common way to share binary data to be written to the target non-volatile memory, such as a EEPROM or microcontroller code flash. Such binary data can contain compiled executable code, configuration data, volatile memory dumps, etc.

The most common file formats for hexadecimal record files are Intel HEX (.hex) and Motorola S-record (.srec). Other common formats for binary data exchange for embedded systems include the Executable and Linkable Format (.elf), hex dumps (by hexdump or xxd), and raw binary files (.bin).

A good thing about hexadecimal record files is that they are almost de-facto, so every time a supplier has to give away its binary data it is either in HEX or SREC, although ELF is arguably the most common for debuggable executables.

A bad thing is that their support in embedded software toolsets is sometimes flawed or only one of the formats is supported, while the supplier provides its binary data in the other format.

Another feature is that binary data is split into text record lines (thus their name) protected by some kind of checksum. This is good for data exchange and line-by-line writing to the target memory (in the old days), but this makes in-place editing by humans rather tedious as data should be split, and the checksum and other metadata have to be updated.

All of the above led to the development of this library, which allows to, for example:

• convert between hexadecimal record formats;
• merge/patch multiple hexadecimal record files of different formats;
• access every single record of a hexadecimal record file;
• build records through handy methods;
• edit sparse data in a virtual memory behaving like a bytearray;
• extract or update only some parts of the binary data.

Documentation

For the full documentation, please refer to:

https://hexrec.readthedocs.io/

Architecture

Within the hexrec package itself are the symbols of the most commonly used classes and functions.

As the core of this library are record files, the hexrec.base is the first module a user should look up. It provides high-level functions to deal with record files, as well as classes holding record data.

The hexrec.base allows to load bytesparse virtual memories, which are as easy to use as the native bytearray, but with sparse data blocks.

The hexrec.utils module provides some miscellaneous utility stuff.

hexrec.xxd is an emulation of the xxd command line utility delivered by vim.

The package can also be run as a command line tool, by running the hexrec package itself (python -m hexrec), providing some record file utilities.

The codebase is written in a simple fashion, to be easily readable and maintainable, following some naive pythonic K.I.S.S. approach by choice.

Examples

To have a glimpse of the features provided by this library, some simple but common examples are shown in the following.

Convert format

It happens that some software tool only supports some hexadecimal record file formats, or the format given to you is not handled properly, or simply you prefer a format against another (e.g. SREC has linear addressing, while HEX is in a segment:offset fashion).

In this example, a HEX file is converted to SREC.

from hexrec import convert

convert('data.hex', 'data.srec')

This can also be done by running hexrec as a command line tool:

$ hexrec convert data.hex data.srec

Alternatively, by executing the package itself:

$ python -m hexrec convert data.hex data.srec

Merge files

It is very common that the board factory prefers to receive a single file to program the microcontroller, because a single file is simpler to manage for them, and might be faster for their workers or machine, where every second counts.

This example shows how to merge a bootloader, an executable, and some configuration data into a single file, in the order they are listed.

from hexrec import merge

in_paths = ['bootloader.hex', 'executable.mot', 'configuration.xtek']
out_path = 'merged.srec'
merge(in_paths, out_path)

Alternatively, these files can be merged via manual load:

from hexrec import load, SrecFile

in_paths = ['bootloader.hex', 'executable.mot', 'configuration.xtek']
in_files = [load(path) for path in in_paths]
out_file = SrecFile().merge(*in_files)
out_file.save('merged.srec')

This can also be accomplished by running the hexrec package itself as a command line tool:

$ hexrec merge bootloader.hex executable.mot configuration.xtek merged.srec

Dataset generator

Let us suppose we are early in the development of the embedded system and we need to test the current executable with some data stored in EEPROM. We lack the software tool to generate such data, and even worse we need to test 100 configurations. For the sake of simplicity, the data structure consists of 4096 random values (0 to 1) of float type, stored in little-endian at the address 0xDA7A0000.

import struct, random
from hexrec import SrecFile

for index in range(100):
    values = [random.random() for _ in range(4096)]
    data = struct.pack('<4096f', *values)
    file = SrecFile.from_bytes(data, offset=0xDA7A0000)
    file.save(f'dataset_{index:02d}.mot')

Write a CRC

Usually, the executable or the configuration data of an embedded system are protected by a CRC, so that their integrity can be self-checked.

Let us suppose that for some reason the compiler does not calculate such CRC the expected way, and we prefer to do it with a script.

This example shows how to load a HEX file, compute a CRC32 from the address 0x1000 to 0x3FFB (0x3FFC exclusive), and write the calculated CRC to 0x3FFC in big-endian as a SREC file. The rest of the data is left untouched.

import binascii, struct
from hexrec import load

file = load('checkme.srec')

with file.view(0x1000, 0x3FFC) as view:
    crc = binascii.crc32(view) & 0xFFFFFFFF  # remove sign

file.write(0x3FFC, struct.pack('>L', crc))
file.save('checkme_crc.srec')

Trim for bootloader

When using a bootloader, it is very important that the application being written does not overlap with the bootloader. Sometimes the compiler still generates stuff like a default interrupt table which should reside in the bootloader, and we need to get rid of it, as well as everything outside the address range allocated for the application itself.

This example shows how to trim the application executable record file to the allocated address range 0x8000-0x1FFFF. Being written to a flash memory, unused memory byte cells default to 0xFF.

from hexrec import load, SrecFile

in_file = load('application.mot')
data = in_file.read(0x8000, 0x1FFFF+1, fill=0xFF)

out_file = SrecFile.from_bytes(data, offset=0x8000)
out_file.save('app_trimmed.mot')

This can also be done by running the hexrec package as a command line tool:

$ hexrec crop -s 0x8000 -e 0x20000 -v 0xFF app_original.hex app_trimmed.srec

By contrast, we need to fill the application range within the bootloader image with 0xFF, so that no existing application will be available again. Also, we need to preserve the address range 0x3F800-0x3FFFF because it already contains some important data.

from hexrec import load

file = load('bootloader.hex')
file.fill(0x8000, 0x1FFFF+1, 0xFF)
file.clear(0x3F800, 0x3FFFF+1)
file.save('boot_fixed.hex')

With the command line interface, it can be done via a two-pass processing, first to fill the application range, then to clear the reserved range. Please note that the first command is chained to the second one via standard output/input buffering (the virtual - file path, in ihex format as per boot_original.hex).

$ hexrec fill -s 0x8000 -e 0x20000 -v 0xFF boot_original.hex - | \
  hexrec clear -s 0x3F800 -e 0x40000 -i ihex - boot_fixed.srec

(newline continuation is backslash \ for a Unix-like shell, caret ^ for a DOS prompt).

Export ELF sections

The following example shows how to export sections stored within an Executable and Linkable File (ELF), compiled for a microcontroller. As per the previous example, only data within the range 0x8000-0x1FFFF are kept, with the rest of the memory filled with the 0xFF value.

from hexrec import SrecFile
from bytesparse import Memory
from elftools.elf.elffile import ELFFile  # "pyelftools" package

with open('appelf.elf', 'rb') as elf_stream:
    elf_file = ELFFile(elf_stream)

    memory = Memory(start=0x8000, endex=0x1FFFF+1)  # bounds set
    memory.fill(pattern=0xFF)  # between bounds

    for section in elf_file.iter_sections():
        if (section.header.sh_flags & 3) == 3:  # SHF_WRITE | SHF_ALLOC
            address = section.header.sh_addr
            data = section.data()
            memory.write(address, data)

out_file = SrecFile.from_memory(memory, header=b'Source: appelf.elf\0')
out_file.save('appelf.srec')

Installation

From PyPI (might not be the latest version found on github):

$ pip install hexrec

From the source code root directory:

$ pip install .

Development

To run the all the tests:

$ pip install tox
$ tox