3.3.12. AHB Slave Control Register

The CM7_AHBSCR characteristics are:

Purpose

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

Usage Constraints

Accessible in privileged mode only.

Configurations

Available in all configurations.

Attributes

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

BitsNameTypeFunction
[31:16]--Reserved.
[15:11]INITCOUNTRW

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

Note

  • 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.

[10:2]TPRIRW

Threshold execution priority for AHBS traffic demotion.

0b0xxxxxxx

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

0b11111111

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

0b11111110

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

[1:0]CTLRW

AHBS prioritization control:

0b00

AHBS access priority demoted. This is the reset value.

0b01

Software access priority demoted.

0b10

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).

Note

  • 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.

0b11

AHBSPRI signal has control of access priority.


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