AN2836 Freescale Semiconductor / Motorola, AN2836 Datasheet - Page 26

• Manufacturer Part Number: AN2836
• Description: Web Server Development with MC9S12NE64 and OpenTCP
• Manufacturer: Freescale Semiconductor / Motorola

Overview of a Web Server Developed Using OpenTCP TCP/IP Stack
Setting for BUFMAP less than 4 are provided to:
The setting of BUFMAP is a system/network design decision. If the devices on your network should only
accept Ethernet packets of a certain size limit, BUFMAP should be configured accordingly.
Setting BUFMAP to create a buffer size limit reduces the burden on CPU from processing larger
undesirable packets on the network. If a receive frame exceeds the receive buffer size, the frame is not
accepted and both receive complete flag or the receive error flag are not set. No CPU bandwidth is used
because the EMAC state machine does all the packet filtering. This is a powerful filtering mechanism.
P&E_ICD_linker.prm also defines the placement of the sections. It is noteworthy to discuss the
MyConstSegPage1 placement
component, NE64DemoNOPIC_file, which is contained in NE64DemoNOPIC.c . Because
NE64DemoNOPIC.c is a constant array, by default, it would be stored in ROM_VAR which causes a
FLASH allocation problem for this project. Creating MyConstSegPage1 and grouping the
NE64DemoNOPIC_file data with DEFAULT_ROM resolves the FLASH allocation problem. More
information on FLASH allocation can be found within the CodeWarrior user manual.
Excerpt from P&E_ICD_linker.prm:
NAMES
END
SECTIONS
//
//
//
//
ROM_4000 = READ_ONLY
ROM_C000 = READ_ONLY
/* banked FLASH ROM */
SECURITY = READ_ONLY
ROM_FF10 = READ_ONLY
26
•
•
RAM
/* unbanked FLASH ROM */
RAM
Maximize user RAM
Provide a filtering mechanism base on Ethernet packet size
RAM
RAM
RAM
BUFMAP
0
1
2
3
4
= READ_WRITE 0x3200 TO 0x3FFE;
= READ_WRITE 0x2C00 TO 0x3FFE;
= READ_WRITE 0x2180 TO 0x3FFE;
= READ_WRITE 0x2300 TO 0x3FFE;
= READ_WRITE 0x2600 TO 0x3FFE;
Web Server Development with MC9S12NE64 and OpenTCP, Rev. 0
0x4000 TO 0x7FFF;
0xC000 TO 0xFEFF;
0xFF00 TO 0xFF0F;
0xFF10 TO 0xFF7F;
Individual Buffer Size
.
MyConstSegPage1 refers to a web server file array for the ActiveX
(bytes)
1.5K
Table 7. Memory Allocation
128
256
512
1K
Ethernet buffer space
/* BUFMAP = 4 (1.5K) */
Total Size of EMAC
/* BUFMAP = 3 (1K) less then means no DHCP*/
/* BUFMAP = 0 (128 byte) */
/* BUFMAP = 1 (256 byte) */
/* BUFMAP = 2 (512 byte) */
1536
3072
4608
384
768
Remainder RAM for
User Application
Freescale Semiconductor
7.625K
7.25K
6.5K
3.5K
5K