Freescale Semiconductor MCF5480 - Manual (Page 172)

MCF548x Reference Manual, Rev. 3
5-6 Freescale Semiconductor
5.2.3.10 ACR Address Improvements
ACRs provide a 16-Mbyte address window. For a given request address, if the ACR is valid and the request
mode matches the mode specified in the supervisor mode field, ACRn[S], hit determination is specified as
follows:
ACRx_Hit = 0;
if ((address[31:24] & ~ACRn[23:16]) == (ACRn[31:24] & ~ACRn[23:16]))
ACRx_Hit = 1;
With this hit function, ACRs can assign address attributes for user or supervisor requests to memory spaces
of at least 16 Mbytes (through the address mask). With the MMU definition, the ACR hit function is
improved by the address mask mode bit (ACRn[AMM]), which supports finer address granularity. See
Table 5-1 .
The revised hit determination becomes the following:
ACRx_Hit = 0;
if (ACRn[10] == 1)
if ((address[31–24] == ACRn[31–24])) &&
((address[23–20] & ~ACRn[19–16]) == (ACRn[23–20] & ~ACRn[19–16])))
ACRx_Hit = 1;
else if (address[31–24] & ~ACRn[23–16]) == (ACRn[31–24] & ~ACRn[23–16]))
ACRx_Hit = 1;
Table 5-1. New ACR and CACR Bits
Bits Name Description
ACRn[10] AMM Address mask mode. Determines access to the associated address space.
0 The ACR hit function is the same as previous versions, allowing control of a 16-Mbyte
or greater memory region.
1 The upper 8 bits of the address and ACR are compared without a mask function; bits
23–20 of the address and ACR are compared masked by ACR[19–16], allowing control
of a 1- to 16-Mbyte region.
Reset value is 0.
ACRn[3] SP Supervisor protect. Determines access to the associated address space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes an access error
exception.
Reset value is 0.
CACR[23] DDSP Default data supervisor protect. Determines access to the associated data space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes an access error
exception.
Reset value is 0.
CACR[7] DISP Default instruction supervisor protect. Determines access to the associated instruction
space.
0 Supervisor and user access allowed.
1 Only supervisor access allowed. Attempted user access causes access error exception
Reset value is 0.