3.5.26. About the counter registers

An ETM implements between zero and four 16-bit counters, and uses four registers to define the operation of each counter. The following sections describe the counter registers:

Table 3.36 summarizes the counter registers:

Table 3.36. Summary of counter registers

 Counter registers
CounterReload Value [a]Enable[a]Reload Event [a]Value[a]

[a] Register numbers are listed. Where registers are accessed in a memory-mapped scheme, the register offset is always 4 x (Register number).

Bits [15:13] of the ETMCCR specify how many counters the ETM implements. See Configuration Code Register, ETMCCR

See Counters for more information about the counter registers.

Reduced function counter, ETMv3.5

In ETMv3.5, counter 1 can be implemented as a counter with reduced functionality. The reduced function counter has the following attributes:

  • 16-bit reload value, configured by ETMCNTRLDVR1

  • Decrements on every cycle. ETMCNTENR1 is Reserved.

  • Reloads every time the counter reaches zero. ETMCNTRLDEVR1 is Reserved.

  • The counter value cannot be read. ETNCNTVR1 is Reserved.

  • The counter always starts at the reload value when the ETM programming bit is cleared.

  • The value cannot be saved or restored.

Bit [27] of the ETMCCER identifies whether counter 1 is a reduced function counter. See Configuration Code Extension Register, ETMCCER, ETMv3.1 and later.

If more than 1 counter is implemented, the counters other than counter 1 are always full function counters.

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