Disabling the

MMU

WO R K I N G W I T H T H E C P U

TLB structure

Care must be taken if the translated address differs from the untranslated address, because several instructions following the enabling of the MMU might have been prefetched with MMU off (VA=MVA=PA). If this happens, enabling the MMU can be considered as a branch with delayed execution. A similar situation occurs when the MMU is disabled. Consider this code sequence:

MRC p15, 0, R1, c1, C0, 0

; Read control register

ORR R1, #0x1

; Set M bit

MCR p15, 0,R1,C1, C0,0

; Write control register and enable MMU

Fetch Flat

 

Fetch Flat

 

Fetch Translated

 

Note: Because the same register (R1: Control register) controls the enabling of ICache, DCache, and the MMU, all three can be enabled using a single MCR instruction.

Clear bit 0 (the M bit) in the R1: Control register to disable the MMU.

Note: If the MMU is enabled, then disabled, then subsequently re-enabled, the contents of the TLB are preserved. If these are now invalid, the TLB must be invalidated before re-enabling the MMU (see “R8:TLB Operations register” on page 97).

T L B s t r u c t u r e

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The MMU runs a single unified TLB used for both data accesses and instruction fetches. The TLB is divided into two parts:

An eight-entry fully-associative part used exclusively for holding locked down TLB entries.

A set-associative part for all other entries.

Whether an entry is placed in the set-associative part or lockdown part of the TLB depends on the state of the TLB Lockdown register when the entry is written into the TLB (see “R10:TLB Lockdown register” on page 101).

When an entry has been written into the lockdown part of the TLB, it can be removed only by being overwritten explicitly or, when the MVA matches the locked down entry, by an MVA-based TLB invalidate operation.

The structure of the set-associative part of the TLB does not form part of the programmer’s model for the ARM926EJ-S processor. No assumptions must be made

126Hardware Reference NS9215

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Digi NS9215 manual B s t r u c t u r e, Disabling
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NS9215 specifications

The Digi NS9215 is a powerful solution designed for industrial applications that require reliable connectivity and robust performance. Built on a foundation of advanced technologies, the NS9215 serves as a versatile networking device that meets the demands of automation, remote monitoring, and data acquisition.

One of the standout features of the Digi NS9215 is its multi-protocol support. It is capable of handling various communication protocols, including Ethernet, Serial, and Wireless, making it ideal for integration into heterogeneous environments. This flexibility enables users to connect legacy devices to modern networks seamlessly, facilitating smoother data communication across different platforms.

The NS9215 is equipped with powerful processing capabilities, featuring an integrated processor that ensures efficient data handling. This enables the device to perform complex data tasks without compromising performance. Its high-speed connectivity options also allow for rapid data transmission, which is crucial for real-time applications in industrial settings.

Another critical characteristic of the Digi NS9215 is its reliability in harsh environments. Built to withstand extreme temperatures, humidity, and electrical interference, this device assures consistent operation even in challenging conditions. Its rugged design minimizes the risk of failure, making it suitable for deployment in various industrial environments.

Security is a top priority for the Digi NS9215. It comes with advanced security features that protect sensitive data during transmission and prevent unauthorized access. Employing encryption protocols and secure authentication methods, the NS9215 ensures that data integrity and confidentiality are maintained throughout its operation.

The user-friendly interface of the NS9215 allows for easy configuration and management. This ease of use reduces the time required for installation and setup, enabling quick deployment in field operations. Additionally, remote management capabilities enhance operational efficiency, allowing users to monitor device performance and make adjustments from anywhere.

Furthermore, the NS9215 supports extensive scalability options. As organizations grow and evolve, the ability to scale up or adapt the networking capabilities becomes essential. With its modular design, the NS9215 can easily accommodate additional devices and protocols, ensuring longevity and continued relevance in a rapidly changing technological landscape.

In conclusion, the Digi NS9215 is a robust networking device designed for a wide range of industrial applications. Its multi-protocol support, reliability, security features, user-friendly interface, and scalability make it a valuable addition to any industrial network infrastructure, delivering performance and efficiency that businesses can depend on for critical operations.
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