Tag: Firmware

For many industrial embedded projects, embedding debugging support (e.g. JTAG) into the design can be immensely useful. This can be for the convenience of integrated debugging or specialized needs, such as galvanic isolation. The FTDI family of High-Speed USB-Serial transceivers are commonly used for this purpose. FTDI’s Multi-Protocol Synchronous Serial Engine (MPSSE) can offload the JTAG state machine and achieve clock speeds as high as 30 MHz. Software like OpenOCD provides a solid basis for manipulating microcontrollers but the situation is very different when it comes to FPGAs.

When writing a freestanding application, it’s generally necessary for the firmware engineer to handle runtime initialization. Even when a library like newlib includes a rudimentary implementation of crt0.o, initialization is a very application-specific process owing to the need to initialize hardware, memory, and other loading tasks.

In this essay, we examine the current and historical implementation of executable initialization, finishing with a minimal implementation usable with firmware applications.

Note: Most firmware applications need to address the initialization of .data and .bss from nonvolatile memory. That is not addressed in this essay.