Freescale Semiconductor SC140 Edca Reference Value Registers a and B EDCAiREFA, EDCAiREFB

Event Detection Unit (EDU) Channels and Registers

the range on bus B, and the two EDCA events should be OR-ed in the event selector. The apparent alternative of detecting the upper range boundary on both buses and the other EDCA to detect the lower range boundary on both buses (AND-ing them in the event selector) may produce erroneous results, for example if two unrelated parallel accesses match the conditions by chance.

When used for data address detection, the EDCA takes into account the access width in order to identify an access to an address that is part of a wide access. Hence, when the data access is 16-bit wide, the LSB of the address does not participate in the comparison.

In a similar way, the following holds true:

—for 16-bit accesses - the LSB of the address is not compared

—for 32-bit accesses (including MOVE.2W) - the 2 LSBs of the address are not compared

—for 64-bit accesses (including MOVE.4W, MOVE.2W) - the 3 LSBs of the address are not compared.

For example, this feature allows setting a watchpoint on address 0x101, in which case the EDCA will also identify it when the core is performing a MOVE.W, MOVE.L, etc. to address $100.

When detection occurs, status bit EDCASTi is set by the EOnCE in the EMCR register. Refer to Table 4-15 on page 4-41.

4.9.1.2EDCA Reference Value Registers A and B (EDCAi_REFA, EDCAi_REFB)

EDCAi_REFA and EDCAi_REFB are 32-bit registers used to hold reference values that are to be compared by the event detection channel comparators. EDCAi_REFA is used by the event detection channel comparator A. EDCAi_REFB is used by the event detection channel comparator B.

4.9.1.3 EDCA Mask Register (EDCAi_MASK)

The EDCAi_MASK is a 32-bit register that allows masking of any one of a sample address’ bits. The sampled address is ANDed with the mask value.

•Mask bits with a value of one stored in them allow the corresponding bit of the selected address to participate in the comparison.

•Mask bits with a value of zero stored in them cause the corresponding bit of the selected address to always match the corresponding bits in the reference value.

The masked address value is then compared to the EDCAi_REFA and EDCAi_REFB registers. For example, the EDCAi_MASK register can be used to detect accesses to a memory region with several address aliases.

SC140 DSP Core Reference Manual 4-57