Microprocessor-based memory card that limits memory accesses by application programs and method of operation

A method comprising:

• (A) providing a microprocessor-based memory card, the memory card having a microprocessor and a memory, the memory including a user memory and a system memory, the user memory having an application program stored therein and the system memory having an operating system stored therein, the application program including memory access instructions that are used by the application program to access the memory, the memory access instructions not being directly executable by the microprocessor but rather requiring interpretation;
• and
• (B) executing the application program using the operating system wherein, for each memory access instruction, the executing step includes the step of interpreting the memory access instruction using an interpreter subprogram, the interpreter subprogam implementing a memory access control interface that controls access to the memory by the memory access instructions based on access clearances stored in a checking zone, the interpreter subprogram being contained in the memory, the memory access instruction being interpreted so as to produce an executable instruction that is directly executable by the microprocessor, the interpreting step further including
• (1) examining the checking zone in the user memory to determine an access clearance associated with the memory access instruction,
• (2) comparing (i) an address specified by the memory access instruction and the type of access required to execute the executable instruction with (ii) the access clearance associated with the memory access instruction, and
• (3) accessing the memory in the manner specified by the memory access instruction only if the access clearance exists for the address specified and the type of access required.

A method comprising:

• (A) providing a microprocessor-based memory card, the memory card having a microprocessor and a memory, the memory including a user memory and a system memory, the user memory having an application program stored therein and the system memory having an operating system stored therein, the application program including memory access instructions that are used by the application program to access the memory, the memory access instructions not being directly executable by the microprocessor but rather requiring interpretation;
• and
• (B) executing the application program using the operating system, the executing step including, for each memory access instruction, the step of interpreting the memory access instruction by executing an executable routine (i) that corresponds to the memory access instruction and (ii) that includes a plurality of executable instructions which are executed by the microprocessor to implement the memory access required by the memory access instruction, the memory access instruction serving as a pointer to an address of the memory at which the executable routine is stored, the executable routine comprising a plurality of instructions that are directly executable by the microprocessor, and the interpreting step further including
• (1) examining a checking zone in the user memory to determine an access clearance associated with the memory access instruction,
• (2) comparing (i) an address specified by the memory access instruction and the type of access required to execute the executable instruction with (ii) the access clearance associated with the memory access instruction, and
• (3) accessing the memory in the manner specified by the memory access instruction only if the access clearance exists for the address specified and the type of access required, and
• wherein the examining, comparing and accessing steps are all performed by the executable routine;
• and
• wherein the interpreting step is performed by an interpreter program that implements a memory access control interface which controls access to the memory by the memory access instructions based on the access clearances stored in the checking zone.