emFTP

SEGGER emFTP is a lightweight FTP server designed for embedded systems that need to provide file transfer access over a network connection. It supports multiple concurrent connections, both Active and Passive FTP modes, and secure transfer via FTPS (implicit TLS) and FTPES (explicit TLS upgrade), covering the full range of FTP deployment scenarios from basic unencrypted transfers in isolated factory networks to TLS-secured connections exposed to broader infrastructure. With a ROM footprint of approximately 5.6 KB on Cortex-M3 and RAM usage starting at around 2.5 KB for a single connection, emFTP adds file transfer capability without placing undue pressure on constrained embedded platforms.

Resource Requirements and FTP Commands

emFTP implements 17 core FTP commands per RFC 959, including USER, PASS, PWD, CWD, LIST, STOR, RETR, DELE, MKD, and RMD. The server runs as a multitasking application with a parent task and one child task per active connection, keeping per-connection RAM overhead to approximately 1.8 KB.

Resource	Requirement
ROM (ARM7)	~6.6 KB
ROM (Cortex-M3)	~5.6 KB
RAM (parent task)	~500 bytes
RAM (per connection)	~1.8 KB
Minimum config	~2.5 KB total (1 connection)
Dependencies	TCP/IP stack with sockets, multitasking OS

Stack Independence and Secure Transfers

emFTP is file system agnostic and TCP/IP stack independent, it works with any RFC-compliant stack through a socket interface and is optimised for SEGGER emNet. For secure deployments, FTPS wraps the entire connection in TLS from the outset, while FTPES starts as a plain connection and upgrades to TLS on demand, providing flexibility for environments with mixed security requirements. An evaluation build for Windows, macOS, and Linux uses the same embedded engine, allowing developers to prototype server behaviour on a desktop before deploying to the target. Royalty-free licensing with a one-time payment model ensures no per-unit costs in production.