MMU 和 MPU的区别

S3C2440里面带的是MMU，而现在流行的Cortex-M3/4 里面带的是MPU。

MMU vs MPU

内存是现代计算机最重要的组件之一。因此，它的内容不能被任何错误的应用所篡改。这个功能可以通过MMU(Memory Management Unit)或者MPU(Memory Protection Unit)来实现。尽管这个两个东西有同样的基本功能，但是它们之间还是存在一些不同。MMU被认为是比MPU更先进的设备。MMU能完成MPU的所有工作，并且它还具备MPU没有的一些高级特性。

MMU具备而MPU不具备的特性包括：缓存控制，总线仲裁，bank切换。这些特性是更复杂的计算机所需要的，以便信息处理流程更顺畅无误。通过使用MMU，你能优化你的计算机性能，因为它可以让微处理器不用关心上述：缓存控制，总线仲裁，bank切换任务，由独立的MMU单元来全权负责。

如果你使用的是简单计算机，不需要做多任务或者相关处理，使用MMU可能不是最好的做法。首先要考虑的是价格和复杂性，因为使用先进的MMU会带来更高的价格和复杂度。相比于简单的MPU,使用MMU会给系统带来不必要的负担。如果主处理器不够快，使用MMU会造成一些问题。

选择MMU还是MPU更大程度上取决于构建系统的规模和复杂度。如果的你系统足够大使用MMU会带来好处。如果你构建一个可靠地简单系统，MMU是不建议选择的。MPU将提供必要的功能，同时降低复杂性和成本。

总结：

MMU比MPU更先进

MMU能覆盖MPU的所有功能

MMU能实现缓存控制，总线仲裁，Bank切换，而MPU不能

MPU比MMU更简单，使用开销也更少

Memory is one important component in modern computing. As such, it is necessary that its contents are not corrupted by any errant application. This function can be done by an MMU (Memory Management Unit) or by an MPU (Memory Protection Unit). Although they both do the same basic function, there are a number of differences between an MMU and an MPU. An MMU is considered to be a more advanced device than an MPU. An MMU is capable of doing the job of an MPU along with other more advanced features that are absent in the latter.

The features that are present in an MMU and not in the MPU include cache control, bus arbitration, and bank switching. All these features are necessary in more complex computers as they allow the flow of information to be smoother and without any problem. By using an MMU, you can also optimize the performance of your computer as it would off-load the said tasks from the microprocessor.

But if you are dealing with a very simple computer that does not do multi-tasking and other related processes, using an MMU may not be the best thing to do. The primary consideration would be price and complexity as employing the more advanced MMU would be more costly and more complex. It may also tax the system unnecessarily as MMU units utilize more overhead compared to the far simpler MPUs. If the main processor used is not fast enough, using an MMU may cause problems.

Choosing between an MMU and MPU is largely dependent on the scale and complexity of the system being built. An MMU is recommended if your system is large enough to benefit from its capabilities. If you are building a relatively simply system, using an MMU is not advisable. An MPU would provide the necessary capabilities while keeping complexity and cost down.

Summary:

An MMU is more advanced than an MPU
An MMU is able to do the job of an MPU
An MMU is capable of cache control while an MPU is not
An MMU is capable of bus arbitration while an MPU is not
An MMU is capable of bank switching while an MPU is not
An MPU is simpler and uses less overhead than an MMU