MOTOROLA
Chapter 22. CALRAM Operation
22-5
Modes of Operation
22.4.1
Reset
Reset configures the CALRAM module and resets some of the bits in the CALRAM
registers to their default reset state. Some register bits are unaffected by reset. See section
22.4.2
One-Cycle Mode
The CALRAM registers and array may be accessed for reads or writes as byte, (aligned)
half-word, or word. This mode is the default mode of operation and, as the name suggests,
the access time to the array and the internal registers for reads and writes is one cycle. Thus
the one-cycle mode is used for high performance although it consumes more power than
the two cycle mode.
22.4.2.1 CALRAM Access/Privilege Violations
Each 8-Kbyte CALRAM array can be assigned read-only, data-only, or supervisor-only
privilege if data relocate (DR) bit in the MSR is set. All CALRAM registers are assigned
supervisor-only and data-only privilege. A privilege violation causes an error. See section
An attempt to access any of the four unimplemented reserved registers (of the 16 register
spaces) causes an error and returns 0’s on the data bus for a read access. If an error condition
occurs due to privilege violation or an attempt to access unimplemented portions of array
or register space, then the type of the error generated depends on whether the access
generating the error was initiated by the RCPU core or by a non-RCPU bus master. If the
error causing access was initiated by the RCPU core, a data storage interrupt (DSI) is
generated. If the access was initiated by a non-RCPU bus master, a machine check
exception is generated. Also, a write access that generates an error does not corrupt the data
in an array or a register. Similarly, a read access that generates an error does not drive the
data on the L-bus from the array or the register, instead it drives 0’s. Also, aborted accesses
maintain data integrity. Aborted writes do not corrupt data in register/array, and aborted
reads do not drive the requested data on L-bus.
22.4.3
Two-Cycle Mode
In this mode, the CALRAM module takes two cycles to complete an access and consumes
less power than in one-cycle mode. It follows the normal one-cycle mode operation except
that the accesses are completed one cycle later. This mode is selected by setting the 2CY
bit in the CRAMMCR register.