3.16.40. OS Save and Restore Register, ETMOSSRR

The ETMOSSRR characteristics are:


Used to save or restore the complete PTM trace register state of the macrocell.

Usage constraints

There are no usage constraints.


This register is only available in PFTv1.0.


See the register summary in Table 3.16.

Figure 3.45 shows the ETMOSSRR bit assignments.

Figure 3.45. ETMOSSRR bit assignments

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Table 3.55 shows the ETMOSSRR bit assignments.

Table 3.55. ETMOSSRR bit assignments




The first access to the register must be a read. On this access:

  • on an OS save, this field returns the number of additional read accesses required to save the PTM trace register settings

  • on an OS restore, this field returns an unknown value, or an implementation defined value.


    On an OS restore, this read must be performed even if it returns an unknown value.

On subsequent accesses the field holds the PTM trace register value being saved or restored.

This register works in conjunction with an internal sequence counter, to save or restore the contents of the PTM trace registers. See Table 3.14 for details of how the PTM registers are split into trace and management registers.

Before accessing this register, you must write the key value, 0xC5ACCE55, to the ETMOSLAR. This write resets the OS save and restore internal sequence counter. Locking the PTM trace registers in this way prevents any change to their contents during the save or restore process.

When you have locked access to the PTM trace registers you must read the ETMOSSRR. The significance of the result returned depends on whether you are performing an OS save or an OS restore:

OS save

The value returned is the number of additional ETMOSSRR accesses required to save or restore the PTM trace registers. After reading this value, you must:

  • save this value, for use for the OS restore

  • perform this number of reads of the ETMOSSRR, saving the returned values to save the status of the PTM trace registers.

  • to restore the PTM trace registers you must perform this number of writes to the ETMOSSRR.

OS restore

The value returned is unknown, or might be implementation defined. After reading this value, you must:

  • discard this value

  • use the number of accesses value saved from the OS save operation to find how many accesses are required to restore the status of the PTM trace registers

  • perform this number of writes to the ETMOSSRR, writing back the status information saved in the OS save operation.

The number of accesses required, and the order and interpretation of the save and restore data, is implementation defined. However, the restore sequence must observe the writable status of all bits of the registers being restored.

Behavior is unpredictable if:

For more information on using the ETMOSSRR, see Power-down support.

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