/ɛks-aɪ-pi/
n. “Running code directly from non-volatile memory without copying it to RAM first.”
XIP, short for eXecute In Place, is a technique used in computing where programs are executed directly from non-volatile memory, such as NOR flash, rather than being loaded into RAM. This approach reduces RAM usage, speeds up startup times for embedded systems, and simplifies memory management in devices with limited resources.
Key characteristics of XIP include:
- Direct Execution: The CPU fetches instructions straight from non-volatile memory.
- Reduced RAM Requirement: Programs don’t need to occupy RAM unless modified at runtime.
- Fast Boot Times: Ideal for embedded devices, microcontrollers, or firmware that must start immediately.
- Dependent on Memory Type: Most commonly used with NOR flash due to its fast random-access capability.
- Limited Flexibility: Not all programs can run XIP efficiently; writable memory is still needed for dynamic data.
A conceptual example of XIP:
// Embedded system startup
CPU begins execution directly from NOR flash
Bootloader > Kernel code > Application code
# No need to load program into RAM firstConceptually, XIP is like reading a book directly from the library shelf without making a photocopy — you get instant access while saving storage space.
In essence, XIP is a crucial optimization for embedded systems and firmware, enabling efficient execution from non-volatile memory, conserving RAM, and improving startup performance.