It is entirely possible to create a project entirely in assembly language. However, in many cases we might still want to reuse some of the C code such as system initialization function and peripheral driver because recreating these codes in assembly can just be too much work.
To do this in Keil MDK, we can use the following steps:
1. Create a project, but without adding the Cortex® Microcontroller Software Interface Standard (CMSIS) software components to the project.
2. Manually copy a start-up code (for example, from one of the previous example project) into a file and name is as an assembly language file (e.g., “startup_stm32l053.s”) and add it to the project.