Disassembling binary code is tedious and often boring work. Going through a 3MByte large binary such as the “os” file would take ages so I decided to cheat a little.
What I was mostly interested in was code that touched the hardware, that really means the GPIO pins. Most of the time when the code accesses GPIO register it loads the base address for the whole bank of GPIO registers into a CPU register and then uses that CPU register with an offset to access the other GPIO registers.
The base address for the GPIO registers is 0x56000000. And the binary code for an ARM instruction loading this value into a register is 0xe3a0?456. The ? is the CPU register number and the 56 at the end is the highest eight bits of the address. Finding instructions as this is trivial, show a hexdump of the file, pipe it to less and use the “/” command in less to search for the bytes making up that instruction:
8-6-2021 (August 6, 2021) is the Snakiest day of the year and it’s also this year’s CircuitPython Day! The day highlights all things CircuitPython and Python on Hardware. See you there!
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.
Have an amazing project to share? The Electronics Show and Tell is every Wednesday at 7pm ET! To join, head over to YouTube and check out the show’s live chat – we’ll post the link there.
