6.5. Debug and system power up

The Debug Port in the DAP provides two pairs of power-on request signals to enable power-up of either the debug domain, or the complete system.

The Debug Port registers must be in an always powered-on domain to enable the system to make power-up requests to a system power controller:

In the majority of cases, it is expected that debuggers power on the complete SoC. If the issue for the debugger relates to energy management, the debugger might require power-up for only the debug domain. In this situation, you can design a system so that the power controller maps onto a bus segment that the DAP can access when only the debug domain is powered-on.

Note

The following apply to both system power-up and debug power-up requests and acknowledgements:

  • CxxxPWRUPREQ must be asserted HIGH in the DP to initiate power-on.

  • The power controller must power-up the corresponding power domains on receiving CxxxPWRUPREQ HIGH, and when it has done so CxxxPWRUPACK must be returned HIGH.

  • Tools can only initiate a DAP internal transfer when both CxxxPWRUPREQ and CxxxPWRUPACK are HIGH for either pair of power control signals.

  • When both CxxxPWRUPREQ and CxxxPWRUPACK are HIGH, the corresponding power domains are powered-on.

  • The removal of a power-on request is initiated by CxxxPWRUPREQ being deasserted. The power controller returns CxxxPWRUPACK LOW when the power removal request is accepted.

The return of CxxxPWRUPACK LOW does not indicate that power has been removed. It indicates the request for power-down has been accepted.

Note

  • It is strongly recommended that the debug power domain is powered-down on deassertion of the power-on request.

  • All other power domains must gracefully power-down unless the system is operating in such a way that removal of power would affect its operation, that is, the system must stay powered-up if the power controller has other requests to maintain power.

  • Before tools can make a new request for power on, ACK must be LOW indicating that a previous request for power-down has been accepted. This ensures that the handshaking mechanism is not violated.

Figure 6.7 shows the timing of the power signals. The DP only permits initiation of DAP transfers to an Access Port between time T2 and T3.

Figure 6.7. Power-up request and acknowledgement timing

To view this graphic, your browser must support the SVG format. Either install a browser with native support, or install an appropriate plugin such as Adobe SVG Viewer.


Table 6.1 shows how the power-up request signals must be connected depending on the power configuration of your system.

Table 6.1. Power-up request and acknowledge signal connections

Power configuration CDBGPWRUPACK/ CDBGPWRUPREQ CSYSPWRUPACK/ CSYSPWRUPREQ

No power management Core, SoC, and debug are always on.

Connect CDBGPWRUPACK to CDBGPWRUPREQ.

Connect CSYSPWRUPACK to CSYSPWRUPREQ.

Core is IEM enabled, or can be shutdown.

No SoC or debug power management.

Connect CDBGPWRUPACK and CDBGPWRUPREQ to system power controller.If CDBGPWRUPREQ is HIGH, ensure that all debug logic is powered up.

Connect CSYSPWRUPACK to CSYSPWRUPREQ.

Core is IEM enabled, or can be shutdown.

SoC can be powered-off.

No separate debug domain. All CoreSight infrastructure powered by SoC domain.

Connect CDBGPWRUPACK and CDBGPWRUPREQ to system power controller.

If CDBGPWRUPREQ is HIGH, ensure that all debug logic is active.

Connect CSYSPWRUPACK and CSYSPWRUPREQ to system power controller.

If CSYSPWRUPREQ is HIGH, ensure that SoC domain is powered-on.

Separate Core, SoC, and debug power domains. All can be powered-on or off independently.

Connect CDBGPWRUPACK and CDBGPWRUPREQ to system power controller.

If CDBGPWRUPREQ is HIGH, ensure that SoC domain is powered on so that all debug logic is active.

Connect CSYSPWRUPACK and CSYSPWRUPREQ to system power controller.

If CSYSPWRUPREQ is HIGH, ensure that the entire system, Core, SoC, and debug domain is powered-on.


Copyright © 2004, 2007, 2010 ARM Limited. All rights reserved.ARM DGI 0012D
Non-ConfidentialID062610