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Address power issues in embedded apps using dual OS

Posted: 11 Jul 2011     Print Version  Bookmark and Share

Keywords:DSP  operating systems  Adaptive voltage scaling 

The SoC provides a system-level memory protection unit (MPU) that can protect a memory region from being overwritten by internal bus masters like the ARM or DSP cores or the DMAs. This feature can be useful during development to debug the IPC software mechanism or detect ill-behaved programs or memory leaks.

For Linux and DSP/BIOS, the IPC is abstracted by a software component called DSPLink. It consists of several modules to provide DSP control and code loading, buffer passing and control, and message passing and control. On the Linux side, it is a kernel mode driver. On the DSP/ BIOS side, it is a regular driver that can be called at the task level.

For applications that use the DSP as an accelerator, DSPLink PROC functions can be used to shutdown the DSP if the application no longer needs its service.

This is adequate for most embedded systems where the ARM is running Linux as the master processor and it's time to disable I/Os and accelerators to go standby. Disabling the DSP will enable more than 91 per cent power savings just on the processor alone, as shown in figure 5.

image name

Figure 5: Up to 90 per cent power reduction can be achieved with existing PM services.

For other states of DSP idle, power savings can be realised by expanding the Linux kernel space platform drivers or creating a user space proxy that uses DSPLink as the message transport to communicate with the DSP/ BIOS side application to send request to PWRM.

For example, to get to an OPP that only idles the DSP (90 per cent power savings), add a service to the Linux suspend framework driver that will send a message to the DSP to initiate a PWRM_sleepDSP operation.

Conclusion
With power management services becoming available in mainline Linux kernel, it is possible to achieve substantial power savings by just "turning them on." I hope that this article will encourage you to look into the hardware features of your platform to see if it is capable of reducing operating power to embrace the "go green" initiative.

To download the PDF version, click here.

- Loc Truong
  Senior Member of C6000 DSP Technical Staff
  Texas Instruments


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