TMU Context Save and Restore

Table of Contents

• Introduction
• Supported Combinations
• Steps to Run the Example
• Sample Output

Introduction

This example demonstrates the Context Save and Restore functionality of TMU. We make use of a software interrupt that will get enabled while the TMU operation is being executed. On receiving this high priority interrupt, the ISR gets invoked which will use the TMU hardware. Due to the context save functionality of the TMU result registers, we can enable the use of TMU in an ISR context while simultaneously used in main function.

When the interrupt is taken and the ISR starts running, the context save can be initiated by writing ‘1’ to CONTEXT_SAVE.SAVE bit. TMU result registers are saved to CSAVE_<*> registers. Context save will happen only after all operations initiated before writing to CONTEXT_SAVE.SAVE are complete. This is to ensure that context save happens at correct point. Even though TMU operations are multi-cycle, the TMU operation will have completed by the time context save operation is initiated in ISR. So no additional measure is needed in ISR. After saving context, the ISR can use the TMU without any restriction.

Here in this eaxmple, we calculate the sin of an input value using TMU operation and store it in a variable. After this an interrupt get enabled, and within the ISR the TMU operations is called which will overwrite the values in the existing result registers, to avoid this the context save functionality is initiated that store the values of the result registers in the corresponding context save registers. Before exiting the ISR, the context restore functionality is enabled which will restore the values present in the context save registers to the correponding result registers. In the main function, we store the value present in the result register in another variable and draw a comparison between the two values that got stored before interrupt and after interrupt.

Flow chart depicting example flow

Supported Combinations

Parameter	Value
CPU + OS	r5fss0-0 nortos
Toolchain	ti-arm-clang
Board	am263px-cc, am263px-lp
Example folder	examples/drivers/tmu/tmu_context_save/

Steps to Run the Example

• When using CCS projects to build, import the CCS project for the required combination and build it using the CCS project menu (see Using SDK with CCS Projects).
• When using makefiles to build, note the required combination and build using make command (see Using SDK with Makefiles)
• Launch a CCS debug session and run the executable, see CCS Launch, Load and Run
• View the console log for results

Sample Output

Shown below is a sample output when the application is run,

TMU Context Save and Restore Test Started ...
TMU Context Save and Restore Example runs for 10 Secs
Value in result register before interrupts occur : -0.087851
Value in result register after interrupts occur : -0.087851
 
TMU Context Save and Restore Test Passed!!
All tests have passed!!