Introduction

1.2ARM TCP/IP requirements

Before beginning a port, you must ensure that the necessary resources are available in the target environment. There must be:

•a processor with spare CPU capacity with an operating system

•a debug monitor

•RAM

•a network interface.

The exact size of these resources varies depending on the features you plan to implement, the performance you require, and how many simultaneous users you have to support.

The following is a brief summary of services that ARM TCP/IP requires from the system:

•at least one network interface device

•a timer that ticks at least once a second

•memory, processing power, and operating system requirements, which are detailed in this section.

1.2.1Memory requirements

It is not possible to provide exact memory requirements, however an estimate can be obtained by examining the results provided by the examples. The values provided in Table 1-1 on page 1-5 are from the menus example (see menus on page C-6). The code was compiled for the ARM7TDMI processor core in Thumb state with ADS, version 1.0.1 and was optimized for code size rather than speed. All figures exclude C runtime libraries, board support, and the Menus application.

The majority of the ipport.h build options (such as, routing, NPDEBUG, NET_STATS, and DHCP_CLIENT) are not defined, so the sizes shown in the table below are smaller than if they had been defined. Packet buffers, that are allocated from the heap at initialization time, are not included in these figures.

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Introduction

Note

The values in Table 1-1 might change with subsequent releases because the code is subject to continuous development.

Table 1-1 ARM7TDMI memory requirements (in bytes) for a basic stack

	Thumb
	code and	Read-write	Zero-init	Thumb	RAM
	read-only	data	data	ROM
	data
IP	6720	8028	408	6804	488
ICMP	664	4	104	668	108
UDP	568	4	16	572	20
TCP	10304	76	172	10380	248
sockets	1652	0	0	1652	0
ARP	1272	20	232	1292	252
Ethernet driver	4303	80	128	4336	208
NV parameters	1336	12	200	1348	212
Totals	26820	276	1260	27096	1536

The compilers place read-only data items, such as strings and constants, into the read-only code area. Therefore, the memory requirements for the code area include these constant data items. When designing your system, you have to estimate the amount of ROM and RAM required:

•The ROM requirement is the sum of the read-only area and the read-write data (the read-write data has pre-initialized values).

•The RAM requirement is the sum of the read-write data and the zero-init data, plus the dynamic memory requirements of the system (for example, network buffers).

TCP and sockets use a large portion of memory. Systems that require only IP and User Datagram Protocol (UDP) services (such as routers and SNMP agents) can remove the TCP and sockets layers to reduce memory requirements.

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Introduction

1.2.2Operating system requirements

The stack requires the following basic services from the target system:

clock tick A clock tick counter must be incremented at regular intervals. See cticks in the section on Timers and multitasking on page 2-8.

memory access

The standard malloc() and free() library calls are ideal. If you do not need a TCP or Dynamic Host Configuration Protocol (DHCP) server, these functions are called at startup time only and can be replaced with a static or partition-based scheme.

multitasking

The stack must obtain CPU cycles to process received packets (and handle timeouts) on a timely basis. Two methods are discussed in Task control on page 2-14.

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