Method for virtually enlarging the stack of a portable data carrier

• US 20040015664A1
• Filed: 07/02/2003
• Published: 01/22/2004
• Est. Priority Date: 08/22/2000
• Status: Active Grant

• Current Assignee: Giesecke + Devrient Mobile Security GmBH (Giesecke & Devrient GmbH)
• Original Assignee: Giesecke & Devrient GmbH
• Inventors: Stocker, Thomas, Ciesinger, Daniel, Frey, Thomas, Merck, Martin
• Granted Patent: US 7,000,071 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• CPC Class Codes: G06Q 20/3552 Downloading or loading of personalisation data
• CPC Class Codes: G07F 7/1008 Active credit-cards provided with means to personalise their use, e.g. with PIN-introduction/comparison system

Abstract

A method is proposed for virtual enlargement of the stack of a portable data carrier (10) allowing reloading of executable program code. To permit the execution of programs requiring a larger stack than that physically present, the stack (26) is segmented into at least two stack segments (30) and their fill state monitored. When complete occupation of a segment (30) is recognized, the oldest stack segment (30) is swapped out to a further storage medium (18). The further storage medium (18) can be a slower memory compared to the stack (26). When sufficient memory space is available in the stack (26) again, the swapped out segment (30) is returned.

Claims

1. A method for virtual enlargement of a data structure of a volatile read-write memory (16) on a portable data carrier that is organized as a stack (26), whereby a fill parameter (GW) describing a fill state for the stack (26) is detected and monitored by comparison with a predetermined limiting value (GW), and a part of the data structure is swapped out to a further storage medium (18, 20) as soon as a predetermined relation between limiting value (GW) and fill parameter is reached, characterized in that the stack (26) is segmented into at least two stack segments (30) and swapping to the further storage medium (18, 20) is effected segment by segment.

2. A method according to claim 1, characterized in that the further storage medium is a read-write memory, in particular a nonvolatile read-write memory (18).

3. A method according to either of the above claims, characterized in that the method additionally includes the following step:

swapping in the stack segment (30) swapped out in step e) to the stack (26) as soon as a predetermined relation between fill parameter and a second limiting value is reached, in particular as soon as the fill parameter is smaller than the second limiting value.

4. A method according to any of the above claims, characterized by the following additional step:

managing a destination address of the stack segment (30) swapped out to the nonvolatile read-write memory (18), preferably in a register in the volatile read-write memory (16), the destination address being incremented by an integral multiple of the segment size with each newly swapped out stack segment (30) and decremented by an integral multiple of the segment size with each stack segment (30) swapped back to the stack (26).

5. A method according to any of the above claims, characterized in that segmentation is effected into segments with the size 2ⁿ⁻

m, where m=1, 2, 3 . . . , 2^m=number number of segmentations and 2ⁿ=size of the stack (26), and m is chosen so as to obtain optimal balancing of the data carrier system.

6. A method according to claim 5, characterized in that the limiting value (GW) and/or the second limiting value matches the size of the segment (30), namely 2ⁿ⁻

m, or an integral multiple of the segment size.

7. A method according to any of the above claims, characterized in that the relation between the limiting value (GW) and the fill parameter in step d) is described by the following relation:

“

Fill parameter≦

limiting value.”

8. A method according to any of the above claims, characterized in that the smart card (10) has an operating system that permits reloading of executable program code.

9. A method according to any of the above claims, characterized in that swapping out and/or in of a stack segment (30) is effected by means of known block-by-block transfer instructions.

10. A method according to any of the above claims, characterized in that the fill parameter is formed as a stack pointer (28).

11. A method according to any of the above claims, characterized in that in step d) the stack segment (30) that is oldest is swapped out.

12. A method according to any of the above claims, characterized in that the swapped out stack segment (30) contains return addresses of subprograms, local variables, intermediate results and/or call parameters.

13. A method according to any of the above claims, characterized in that a management of the stack (26), in particular steps a), b), c), d) and optionally steps e) and f), are implemented in hardware.

16. A portable data carrier according to claim 14, characterized in that the microcontroller (32) additionally has a page controller (34) designed for carrying out a method according to any of claims 1 to 10 for swapping out a segment (30) to the nonvolatile memory (18, 20).

14. A portable data carrier (10) having a microcontroller (32) consisting at least of a processor (12), an I/O unit (14), at least one volatile read-write memory (16) with a stack (26), at least one nonvolatile memory (18, 20), an operating system (22) and a data, control and address bus (24), characterized in that the operating system (22) has means for segmenting the stack (26) and for swapping out at least one segment (30) of the volatile read-write memory (16) to the nonvolatile memory (18, 20) when a defined fill state is exceeded.

15. A portable data carrier according to claim 14, characterized in that the nonvolatile memory is a nonvolatile read-write memory (18).