Microcontroller User's Manual

MOTOROLA Chapter 8. System Control Module (SCM) 8-15
System Access Control Unit (SACU)
It should be noted that while the bus does not implement the concept of reference type (code
versus data) and only supports the user/supervisor privilege level, the reference type
attribute is supported by the system bus. Accordingly, the access checking associated with
both privilege level and reference type is performed in the IPS controller using the
attributes associated with the reference from the system bus.
The SACU partitions the access control mechanisms into three distinct functions:
• Master privilege register (MPR)
— Allows each bus master to be assigned a privilege level:
– Disable the master’s user/supervisor attribute and force to user mode access
– Enable the master’s user/supervisor attribute
— The reset state provides supervisor privilege to the processor core (bus master 0).
— Input signals allow the non-core bus masters to have their user/supervisor
attribute enabled at reset. This is intended to support the concept of a trusted bus
master, and also controls the ability of a bus master to modify the register state
of any of the SACU control registers; that is, only trusted masters can modify the
control registers.
• Peripheral access control registers (PACRs)
— Nine 8-bit registers control access to 17 of the on-chip peripheral modules.
— Provides read/write access rights, supervisor/user privilege levels
• Reset state provides supervisor-only read/write access to these modulesGrouped
peripheral access control registers (GPACR0, GPACR1)
— One single register (GPACR0) controls access to 14 of the on-chip peripheral
modules
— One register (GPACR1) controls access for IPS reads and writes to the Flash
module
— Provide read/write/execute access rights, supervisor/user privilege levels
— Reset state provides supervisor-only read/write access to each of these peripheral
spaces
8.6.3 Memory Map/Register Definition
The memory map for the SACU program-visible registers within the System Control
Module (SCM) is shown in Figure 8-8. The MPR, PACR, and GPACRs are 8 bits in width.
Table 8-8. SACU Register Memory Map
IPSBAR
Offset
[31:28] [27:24] [23:20] [19:16] [15:12] [11:8] [7:4] [3:0]
0x020 MPR ——————
0x024 PACR0 PACR1 PACR2 PACR3