The invention applies according to a special form of realisation, to a portable object such as an integrated circuit card. The integrated circuit cards may be for example memory cards or microprocessor cards.

In the context of the invention, the term"portable object"must be taken in its broadest sense. It concerns in particular all types of light terminals equipped with an electronic chip and more especially the smart cards as such.

The electronic chip is itself equipped with information processing means (for example a microprocessor) and information storage means.

TECHNICAL FIELD Currently, a new non volatile memory technology is emerging in smart cards: Flash technology. The Flash memory is organised in sectors as shown on figure 1 (sectors 1,2 and 3). Each sector is a memory block of unique size. The memory space of each sector is divided into memory pages, for example of 128 bytes, grouped into partitions or segments (e. g.: partition Appli1, partition Appli2, partition Appli3 and partition OS of sector 1 on figure 1), used to store various software modules (Appli1, Appli2, Appli3, OS). A partition contains all pages of a sector allocated to a given owner.

In the multi-application cards, several applications may share the same sector (for example, applications 1,2 and 3 share sector 1 on figure 1).

The access controllers of known type provide a given application with write access to a sector it owns or shares. In the Flash memory, a sector defines the unit of erasable memory: consequently to modify a non-blank area of the sector, for example a partition, the entire sector must be erased. To write in a non-blank area of a sector, the entire sector is erased: a sector forms an indivisible unit for

erasure. As shown on figure 1 therefore, if application 1 wants to modify sector 1, it could erase the data of application 2 or even of the operating system. When erasing before writing, partitions containing data belonging to other applications could suffer irrevocable damage.

One known solution is to allocate an entire sector to a single owner. When the sector is large, however, there is a significant loss of memory space and poor flexibility.

One objective of this invention is to optimise the write operation in a Flash memory.

SUMMARY OF THE INVENTION This invention concerns a method to control the access to a sector of a flash type memory of an electronic module which consists in checking that the owner of the data to be written has write access to a partition of said sector characterised in that it consists in checking at least one additional rule on the sector concerned in order to allow possible erasure of the entire said sector before writing in it.

This invention also concerns the electronic module including information processing means, a FLASH type non volatile memory characterised in that it includes a memory manager which consists in checking on the sector concerned at least one rule in addition to that which consists in checking that the owner of the data to be written has write access to a partition of said sector, in order to authorise possible erasure of the entire said sector before writing in it.

BRIEF DESCRIPTION OF THE DRAWINGS Other purposes, features and advantages of the invention will appear on reading the description which follows of the implementation of the method according to the invention and of a mode of realisation of an electronic system designed for this implementation, given as a non-limiting example, and referring to the attached drawings in which:

Figure 1 is a diagrammatic representation of the organisation of a Flash memory; - Figure 2 is a diagrammatic representation of a non-limiting mode of realisation of an electronic unit with microprocessor designed to use the method according to the invention; - Figure 3 is a diagrammatic representation of the various software and hardware layers of the access control system according to this invention.

WAY OF REALISING THE INVENTION The method according to the invention aims to optimise the write in a Flash memory of an electronic system such as for example any portable object equipped with an electronic module and more especially an integrated circuit card.

The electronic system comprises at least a processor and a Flash type non volatile memory. In the following description, FLASH type memory means any memory organised in sectors, the sector forming an indivisible unit for erasure, the sector being itself subdivided into memory pages which could be allocated to different owners.

As a non-limiting example, the electronic system described below corresponds to a portable object comprising an electronic module 1 illustrated on figure 1. This type of module is generally realised as a monolithic integrated electronic microcircuit, or chip, which once physically protected by any known means can be assembled on a portable object such as for example a smart card, integrated circuit card or other card which can be used in various fields.

The microprocessor electronic module 1 comprises a microprocessor CPU 3 with a two-way connection via an internal bus 5 to a Flash type non volatile memory 7 containing applications 9, appli1, appli2, appli3, to be executed, a volatile memory 11 of type RAM, input/output means 1/0 13 to communicate with the exterior.

As represented on figure 3, from the hardware layer consisting of the Flash memory 7 and an access controller 15 controlling access to the memory 7,

we can identify a software layer comprising a memory manager 17 associated or not with a pilot 19 and a software layer comprising resident applications 21 for example a program of the operating system and"user"applications 23 corresponding to precise features (for example an integrated circuit card: bank card, health card, identity card). This representation provides a diagrammatic illustration of the memory access control system only, bearing in mind that the hardware and software layers comprise many other modules performing various tasks.

The access controller 15 checks that a user wanting to access an address in the memory has the necessary rights. Generally, the access controller 15 can be realised as windows open on a series of pages (such as a segmentation device MPU) or as semi-static access matrices associating attributes to the pages (partition type device MAC). Applications are associated with memory areas either during configuration or when selecting an application. Such mechanisms only allow memory access for predetermined code/data area pairs. With an access matrix, for example, the role of the access controller at the time of execution simply consists in comparing the identity of the page"owner"and the identity of the module trying to access this page.

According to this invention, the memory manager 17 intercepts the writes in Flash memory 7 and performs an additional check on the sector concerned before authorising or not erasure of the sector following the write. The check determines whether the erasure caused by the write would not delete data belonging to other owners. In this description, the term"data"covers any type of information stored in the memory, whether code, data or other. Writes must never be made directly in memory nor by direct call to a pilot, but be made via said memory manager. The manager can also check the write access rights in the page indicated.

The method according to the invention consists, using the memory manager, in checking a set of rules for the entire sector concerned, to authorise the erasure of a sector before writing in it.

The set of rules concerning the sector takes into consideration the owner (s) of the pages in the segment concerned and the content of the pages.

The set of rules checks that the write cannot delete data which must be kept and

in particular data of an owner other than the user wanting to make the write.

The check is therefore based on one or more rules of the following type: - The write is authorised if: o the location in the sector where the write is to be made is blank, bearing in mind that the sector is not necessarily completely blank ; the write does not result in erasure; o And/or the entire sector belongs to the same owner; o And/or the pages not belonging to the same owner are blank ; o And/or the pages not belonging to the same owner are marked as erasable; In this description, a sector is said to be blank when no write has been made in the sector or when the sector has been erased and no new write has been made since the erasure.

According to a special form of realisation of the invention, the module according to this invention comprises all of these rules.

The manager has: - a memory description 27 stored in memory: o a number of sectors o a number of pages per sector o an owner of each page o the statuses of the pages (erasable, blank or not blank) - a description of the current request: o the sector concerned (from the address) o the owner issuing the request - and a set of rules 29.

The memory manager allows an owner to mark the pages belonging to him as erasable. As seen previously, the manager keeps the statuses of the pages marked as erasable in the description 27.

In addition, the memory manager must respect the following conditions: - The check code must be executed with the privileges required to authorise or not the erasure of a sector;

- All memory accesses must be made via this manager; - It must not be possible for the code to be changed by the code of another unauthorised owner.

A simple application program interface (API) 25 based on the previous constraints could include, for example, the following functions: - error nv write (dst addr, src addr, length) : o dstaddr : destination address where the data will be written o srcaddr : source address from which the data to be written will be read o length : length of the data to be written.

This function is used to write in memory the data read at a given address after checking the set of rules.

- error nv-fill (dst-addr, pattern, length) : o dstaddr : destination address from which the memory will be filled with the required pattern o pattern: byte to be reproduced o length : length of the area to be filled This function is used to write in memory the data of a"pattern"after checking the set of rules.

In the example illustrated on figure 1, if the applications and the operating system do not authorise any modification or any erasure by a third party: o In sector 1, the manager will not authorise any applications nor the operating system to erase the sector since the sector is divided into 4 partitions belonging to different owners and no owner authorises his neighbour to modify his own partition. The sector can only be erased if the 4 partitions are marked by their owners as erasable. o For sector 2, the manager will authorise application No.

2 to erase its own partition since the rest of the sector is blank ; o For sector 3, since the sector belongs entirely to the operating system, the operating system has all the rights on this sector. It can therefore erase it.