AT697E datasheet(19/154 Pages) ATMEL

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AT697

4226G–AERO–05/09

Watch Points

The integer unit contains four hardware watch-points allowing generation of a trap on an

arbitrary memory address range. Any binary aligned address range can be watched (the

two less significant bits are ignored)

Each watch-point consists in a pair of application-specific registers

•

break address register

The break address defines a reference address for testing.

•

mask register

The mask indicates which bits of the break address register are to be effectively

taken in account during address test

Configuration

A watchpoint is enabled setting logical one at least one of the three bits IF, Dl or DS in

the watchpoint address and mask registers. When all three bits are set logical zero, the

watchpoint is disabled.

If the instruction fetch bit (IF) from the watchpoint address register is set logical one, any

attempt to fetch an instruction from one of the address defined by ADDR and MASK

results in a trap generation.

If the data store bit (DS) from the watchpoint address register is set logical one, any

attempt to store data to one of the address defined by ADDR and MASK results in a trap

generation.

If the data load bit (DL) from the watchpoint mask register is set logical one, any attempt

to load a data from one of the address defined by ADDR and MASK results in a trap

generation.

Operation

To detect if an address is part of the memory address range that traps, address bit 31

down to bit 2 are Xored with the ADDR field from the watchpoint address register.

This operation is based on the following segmentation of an address.

Table 7. Address Segmentation

With such segmentation, it is possible to define trap segment from 4bytes up to 1Gbyte.

The result of the Xor is then Anded with the MASK field of the watchpoint mask register.

If the result is zero, this indicates that address specified is in the watched range. Then, a

watchpoint hit error is generated. Trap 0x0B is generated. If result is different from zero,

address is out of the watched address range.

Figure 6. Watchpoint Hit Principle

bit num. 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9

field

Address

ignored

Watchpoint Address Reg.

%asrx

Trap 0x0B

Watchpoint Mask Reg.

%asry

logic

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