emNet IP X Config

IP_X_Config

Overview

IP_X_Config is a configuration function used by the emNet IP stack during initialization (IP_Init()). Its primary purpose is to assign memory, configure buffers, set TCP/UDP parameters, and initialize network interfaces.

Memory Pool Configuration

The emNet stack uses a shared memory pool defined by ALLOC_SIZE. This pool is dynamically allocated and shared between:

• Protocol buffers (Tx/Rx)
• Driver transfer memory
• TCP/UDP sockets
• Extensions (IPv6, DHCP, VLAN, multiple interfaces, etc.)

Choosing ALLOC_SIZE

The correct value of ALLOC_SIZE is critical for system stability:

• It depends on the number and size of buffers, the configured MTU, driver requirements, and enabled features.
• If ALLOC_SIZE is too small, the stack may run out of memory at runtime.
• Overhead must be added for:
  • System-specific alignment constraints
  • Memory management overhead

Example Configurations

Different system profiles require different ALLOC_SIZE values:

System Profile	MTU	Small Buffers	Big Buffers	TCP Window (Tx/Rx)	Notes
Microcontroller, minimum size	576	4 * 256	3 * (mtu+16)	2*(mtu-40) / 1*(mtu-40)	Optimized for minimal RAM
Microcontroller, size optimized	576	8 * 256	4 * (mtu+16)	2*(mtu-40) / 2*(mtu-40)	Balanced memory usage
Microcontroller, speed/multi-conn.	1500	12 * 256	6 * (mtu+16)	3*(mtu-40) / 3*(mtu-40)	Higher throughput
System with lots of RAM	1500	50 * 256	50 * (mtu+16)	8*(mtu-40) / 8*(mtu-40)	Large-scale systems

Notes

• The MTU (Maximum Transmission Unit) ranges from 576 (RFC minimum) to 1500 (Ethernet maximum).
• Large buffers must always be sized as MTU + 16 to accommodate Ethernet headers.
• TCP Tx space should allow at least two full packets.
• Systems with more RAM can allocate significantly larger pools for higher performance and multiple connections.