4.9.4. AHB Slave Control Register


This register is optional and might not be available in your implementation.

The AHBSCR is used by software to control the priority of AHB slave traffic. The bit assignments are:

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Table 4.72. AHBSCR bit assignments


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


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

  • INITCOUNT must not be set to 0b00 because the demoted requestor always takes priority when contention occurs, which can lead to livelock.

  • INITCOUNT is not used when 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 AHBSCR.INITCOUNT value when the software execution priority is higher than or equal to the threshold level programmed in 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.


AHBSPRI signal has control of access priority.

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