Electrical computers and digital processing systems: support – Digital data processing system initialization or configuration – Loading initialization program
Reexamination Certificate
1998-11-18
2001-09-25
Butler, Dennis M. (Department: 2182)
Electrical computers and digital processing systems: support
Digital data processing system initialization or configuration
Loading initialization program
Reexamination Certificate
active
06295603
ABSTRACT:
BACKGROUND OF THE INVENTION:
Field of the Invention:
The invention lies in the field of electronics and relates, in particular, to a program-controlled unit which is enabled to select individual segments for use from an available memory by using a segment pointer.
Program-controlled units of this type are, for example, microprocessors, microcontrollers, or signal processors. As a rule, they are designed to execute programs straight away from the beginning (from the time when they are switched on or reset). The programs to be executed, more precisely the program codes representing the programs, may thereby be stored in program memories provided in the program-controlled unit or be read into the program-controlled unit externally via an interface to an external memory or a serial interface.
The fundamental structure of a program-controlled unit in which all of the above-mentioned possibilities are optionally available is illustrated in
FIG. 3. A
program-controlled unit
1
shown there comprises a central processing unit (CPU)
11
, a first read-only memory in the form of a first ROM
12
, a second read-only memory in the form of a second ROM
13
, an internal random-access memory in the form of an internal RAM
14
, a (memory) interface
15
for connecting the program-controlled unit
1
to a non-illustrated external memory and a serial interface
16
.
The program which is intended to be executed when the program-controlled unit
1
is started up or is reset may be stored in the first ROM
12
, in the second ROM
13
, or in the external memory.
Whether the startup program that is executed when the program-controlled unit is started up or on reset is a program stored in the first ROM
12
, a program stored in the second ROM
13
or a program stored in the external memory, depends on the addresses under which the respective memories can be addressed at the relevant point in time. The program to be executed after the program-controlled unit has been started up or reset is read out by the program-controlled unit in standard fashion, starting from a quite specific address. In the exemplary embodiment, the address is equal to zero. If it is the first ROM
12
which can be addressed via the address 0, then the program which is stored in the first ROM
12
starting from the location which can be addressed by the address 0 is executed. If it is the second ROM
13
which can be addressed via the address 0, then the program stored in the second ROM
13
starting from the location which can be addressed by the address 0 is executed. If it is the external memory that can be addressed via the address 0, then the program stored in the external memory starting from the location that can be addressed by the address 0 is executed.
Programs stored within the program-controlled unit are, for example, the so-called bootstrap loaders. A bootstrap loader is a program which enables the following to be instigated: data representing programs are read in via the serial interface
16
of the program-controlled unit
1
, are stored in the internal RAM
14
and, finally, are read from the latter and executed.
The bootstrap loader is stored in the second ROM
13
in the exemplary embodiment. In order that the bootstrap loader is executed after the program-controlled unit has been started up or reset, it is necessary to ensure that the second ROM
13
, more precisely the location starting from which the bootstrap loader is stored therein, can be addressed via the address 0. This is done by mapping the second ROM
13
, at least during the execution of the bootstrap loader, onto that location of the memory area (which can be addressed by the program-controlled unit) at which the read-out of the program code is begun after the program-controlled unit has been switched on or reset.
As a result of the mapping, the relevant memory is temporarily allocated specific addresses; consequently, specific memory regions can selectively be inserted into the memory space (which is addressable by the program-controlled unit) or be blanked out therefrom.
If a program stored in the first ROM
12
or in the external memory is intended to be executed, rather than the bootstrap loader, after the program-controlled unit has been started up or reset, then the first ROM
12
or the external memory must be made addressable via the address 0 by means of mapping.
Mapping is associated with a quite considerable outlay in terms of management and organizational resources.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a program-controlled unit, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which minimizes the outlay for the execution of the bootstrap loader.
With the foregoing and other objects in view there is provided, in accordance with the invention, a program-controlled unit of the type selecting individual memory segments from a memory whereby a segment pointer identifies the memory segment to be accessed, wherein the improvement comprises:
a segment pointer having a content that can be changed prior to an execution by the program-controlled unit of a program to be executed during a boot-up of the program-controlled unit.
With the above and other objects in view there is also provided, in accordance with the invention, a method of operating a program-controlled unit, which comprises:
selecting individual memory segments from an available memory by setting a segment pointer; and
selectively setting a content of the segment pointer prior to executing a bootstrap loading operation with the program-controlled unit.
As a result, the program to be executed after the starting up or resetting of the program-controlled unit no longer has to be stored at a quite specific location. It must—if at all—be stored, should the need arise, at a specific location within any desired memory segment. Since the memory can be subdivided into a multiplicity of memory segments, a multiplicity of programs to be executed after the starting up or resetting of the program-controlled unit can be stored in the memory. It is thus possible—unlike the prior art situation—that each of these programs can be read out and executed without the respective memory segments being mapped onto a specific location.
The relatively complicated mapping in the context of memory segmentation has consequently been replaced by individual setting of the memory segment to be addressed.
The outlay for execution of the bootstrap loader can thereby be reduced to a minimum.
In accordance with an added feature of the invention, the memory segments are at least partially formed by an internal memory of the program-controlled unit.
In accordance with another feature of the invention, the internal memory of the program-controlled unit defines memory segments having an ordinal number 2 and/or greater.
In accordance with an additional feature of the invention, the internal memory of the program-controlled unit is a flash EPROM. In other words, the invention facilitates the replacement of the internal ROMs of the program-controlled unit by so-called flash EPROMs.
The use of flash EPROMs instead of the normal ROMs has been risky heretofore because there was the danger that the bootstrap loader might be inadvertently erased and/or overwritten by a nonexecutable program or one not running as desired: at the address at which the bootstrap loader has had to be located heretofore in order to be executed after the starting up or resetting of the program-controlled unit, sometimes certain other items of information, data or programs, such as interrupt vector tables, for example, must also be present during “normal” operation of the program-controlled unit. If the bootstrap loader is overwritten by these items of information, the program-controlled unit can no longer be started or rebooted with the execution of the bootstrap loader or at any rate can only be started after complicated procedures. Such inadvertence can now be precluded with high probability because the bootstrap loader in the case of th
Butler Dennis M.
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
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