BR - Set or Alter a Debug Register Breakpoint

Set or alter a sticky breakpoint. using the debug registers.

Syntax:

───┬─ BR  ─┬─┬─ E  ─┬─ addr ─┬──────┬─┬─────────────────────┬─
     └─ BRn ─┘ ├─ Wb ─┤        └─ pc ─┘ ├─── , ─── cmd ───────┤
               ├─ Rb ─┤                 └─ , " ─── cmd ─┬─ " ─┘
               └─ Ib ─┘                                │
                                                └── ; ──┘

Parameters:

n

Explicitly specifies a breakpoint number to be assigned to this breakpoint. A value from 0 to 9 may be specified but from this range only a total of 4 may specify enabled debug register breakpoints.

If a value n is specified there must be no space between the number and the BR command.

The default is to assign the lowest available number. If all 10 breakpoint numbers have been assigned then the following message appears:

Too many breakpoints

If all four debug registers are in use then the message:

Out of debug registers

is displayed.

Note:

A disabled debug register breakpoint does not commit the use of a debug register. Thus more that 4 debug register breakpoints may be defined, but only a maximum of 4 enabled at any time.

See the BE and BD commands for information on enabling and disabling breakpoints.

E
Specifies that the breakpoint is to fire when an instruction at the breakpoint address is fetched for execution.

This is mutually exclusive with the W and R parameters.

Rb
Specifies that the breakpoint is to fire when storage at the breakpoint address, for length b is referenced. b may specify 1, 2 or 4 bytes and defaults to 1 byte if left blank.

This is mutually exclusive with the W, I and E parameters.

Wb
Specifies that the breakpoint is to fire when storage at the breakpoint address, for length b is stored. b may specify 1, 2 or 4 bytes and defaults to 1 byte if left blank.

This is mutually exclusive with the R, I and E parameters.

Ib
Specifies that the breakpoint is to fire when data is read or written from an I/O port address specified by addr. The length operand, b is used by the processor to mask out the low order bits of the I/O address. Thus:

     BR I2 %13f

places an I/O breakpoint on ports 13c - 13f. b may specify 1, 2 or 4 bytes and defaults to 1 byte if left blank.

Note that the IO port address must be specified as a linear address, otherwise the expression evaluator will attempt to use the base address of the current CS register to resolve the address parameter.

This is mutually exclusive with the R, W and E parameters.

Note: I/O breakpoints are only available to Pentium processors. Support for this was introduced from fix pack 29 of Warp 3.0 and base Warp 4.0, however a bug has prevented them from working correctly until Fix Pack 0 of Warp 4.0 and Fix Pack 39 of Warp 3.0.

addr
The address of the breakpoint.

The Kernel Debugger converts the address to a linear address before setting up the debug registers. If the address is invalid the definition is retained but marked disabled and invalid.

Note: Real addresses may not be used with debug register breakpoints.

passcount
Specifies the number of times the breakpoint may be passed before the Kernel Debugger is entered. Each time the breakpoint is passed the count is decremented by 1 until 1 is reached. When the breakpoint is encountered with a count of 1 then it will fire and the Kernel Debugger will be entered. Thus if passcount is 5 then the breakpoint will fire on the 5th encounter.

The default passcount is 1, that is the breakpoint will fire on first encounter.

cmd
Specifies a command to be executed when the breakpoint fires. More than one command may be specified by using a semi-colon separator and enclosing the entire command list in single or double quotes.

If no command string is specified then the default command string, as specified by the Z command will be executed.

Note: The command list must be preceded by a comma, unlike the BP command where the comma is optional.

Results & Notes:

If the specified address is valid then the breakpoint definition is accepted and enabled otherwise it is accepted but disabled and one of the following messages is generated:

Invalid selector: selector:offsetPast end of segment selector:offset

If the break-point is successfully defined then the in-built mnemonic BRn, where n corresponds to the break-point number, takes the value of the break-point address. This may be used in any address expression or any command.

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