3.3.12. AHB Slave Control Register

The CM7_AHBSCR characteristics are:


Controls the priority between software and AHB slave access to TCMs. See AHBS interface arbitration.

Usage Constraints

Accessible in privileged mode only.


Available in all configurations.


See the register summary in Table 3.1.

Figure 3.12 shows the CM7_AHBSCR bit assignments.

Figure 3.12. CM7_AHBSCR bit assignments

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Table 3.15 shows the CM7_AHBSCR bit assignments.

Table 3.15. CM7_AHBSCR bit assignments


Fairness counter initialization value. Use to demote access priority of the requestor selected by the CM7_AHBSCR.CTL field. The reset value is 0b01.


  • For round-robin mode set INITCOUNT to 0b01 and CM7_AHBSCR.CTL to 0b00 or 0b01.

  • INITCOUNT must not be set to 0b00 because the demoted requestor then always takes priority when contention occurs, and might cause livelock.

  • INITCOUNT is not used when CM7_AHBSCR.CTL is 0b11.


Threshold execution priority for AHBS traffic demotion.


Priority is TPRI[7:0]. This is the same as the NVIC register encodings.


Priority of -1. This is the priority of the HardFault exception.


Priority of -2. This is the priority of the NMI exception.


AHBS prioritization control:


AHBS access priority demoted. This is the reset value.


Software access priority demoted.


AHBS access priority demoted by initializing the fairness counter to the CM7_AHBSCR.INITCOUNT value when the software execution priority is higher than or equal to the threshold level programmed in CM7_AHBSCR.TPRI. When the software execution priority is below this value, the fairness counter is initialized with 1 (round-robin).


  • The threshold level encoding matches the NVIC encoding and uses arithmetically larger numbers to represent lower priority.

  • The current execution priority of the processor is defined architecturally and includes the effect of the PRIMASK, BASEPRI, and FAULTMASK special-purpose registers.


AHBSPRI signal has control of access priority.

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