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Freescale MQX Release Notes

Freescale Semiconductor

5 Known Issues

5.1 Performance of Code Running in MRAM

As described above, the “Ext. MRAM Debug” build-target provides the most convenient way how to

download and run code on the M52259EVB board. One limitation of this solution is that the code

runtime performance is approximately 8x degraded comparing to Flash-based execution. MRAM is

an external memory device connected to the ColdFire core by 8-bit data bus and having one wait-

state generated for each access. In order to fetch one 32-bit value (instruction) from the MRAM

memory, four accesses need to occur – each inserting one wait-state clock.

This behavior is normal by design.

5.2 Network Communication Performance and Delayed ACKs

Significant differences in performance of host to target TCP communication can be observed,

depending on which client operating system is used. These differences are a result of the

difference in implementation of the TCP delayed ACK algorithm.

Linux is more aggressive in acknowledging packets, and temporarily disables the delayed ACK

algorithm on connection startup. As a result, there is no performance issue observed with Linux-

based browsers (Mozilla Firefox tested).

Microsoft Windows based operating systems take a common approach to implementing the delayed

ACK algorithm. As a result, web server performance can be significantly worse when it is accessed

from Microsoft Windows-based browsers (Internet Explorer and Mozilla Firefox tested). This issue

and a workaround are described at http://support.microsoft.com/kb/328890

This issue is not directly related to the RTCS stack, however limited RAM resources on MCF52259

imply lower buffer and data window sizes, making it more difficult to work around the issue in RTCS

software.

5.3 “HVAC” Demo Applications

In the maximal configuration, the HVAC and WEB_HVAC demo applications are supposed to

demonstrate simultaneous operation of several key MQX features:

‐ MQX RTOS real-world multi-tasking application

‐ MQX BSP and I/O drivers (Ethernet, UART, GPIO)

‐ RTCS TCP/IP network stack with FTP, Telnet or HTTP server

‐ USB Host driver with Mass Storage Class Driver

‐ MFS File System used to access the USB stick directories and files

Total RAM requirements for all of the features are very close to 64k, which is the amount of memory

available on MCF52259 device. The application performance may be significantly affected if more

RAM needs to be allocated at run-time. Also memory fragmentation may occur after some time ,

which may cause problems in network or USB communication.

You can use the debugger and the TAD “memory blocks” screen to see the status of the memory

pool and amount of remaining free memory.

What may cause higher RAM allocation or memory fragmentation?

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ADC Release 3.1 Manual de usuario Pagina 25