[Guruprasad vadhiraj]

Hi friends,

Iam working on cortex m3 (NXP1768). i have question regarding cortex m3

since it does not have MMU
1. how the operationg system is ported on these?.
2. who does the functionality of MMU if os can be ported?
3. ARM said that uClinux has to be used. Does this mean that other os cannot be ported? ,
4. what is the max clock frequency of core?

Guru

[isogen74]

(1) Not all operating systems need an MMU. Most controller RTOS use flat memory an an MPU - which is exactly what the M3 gives you.
(2) Why do you need the functionality of an MMU in a microcontroller OS?
(3) uClinux is a version of Linux ported to ... use a flat map memory and an MPU like an RTOS. Pretty much every commercial RTOS will run without an MMU.
(4) It depends on the implementation - look at the datasheets from the various SoC manufacturers. For the LPC1700 series they are rated at 120Mhz max frequency.

[Tamir]

(2) Why do you need the functionality of an MMU in a microcontroller OS?

To guard OS data structure from corruption...?

[isogen74]

Quote

To guard OS data structure from corruption...?

You don't need an MMU to provide protection of critical data - although it can be used for that - the MPU in the Cortex-M and Cortex-R series does that job perfectly well.

The extra feature an MMU provides is virtual memory - the ability to remap a physical address into a different virtual address - I don't understand why you need that in an RTOS. [I's a rhetorical quesution really - the anser is "you don't", hence why most micro-controllers support and MPU and not an MMU].

Iso

[Tamir]

Ache, I saw "MPU" where I should have read "MMU"...you are right!