Image data processing circuit and method of accessing storing means for the processing circuit

A method of accessing a storing means which is shared between two image data processing circuits which are asynchronously operated, comprising the steps of:

• determining a common access asynchronous clock in a case where the two image data processing circuits access the storing means;
• determining an order of priority for access to the storing means between the two image data processing circuits;
• interrupting access to the storing means by a lower-priority image data processing circuit when a higher-priority image data processing circuit requests access to the storing means while the lower-priority image data processing circuit is accessing the storing means to cause the higher-priority image data processing circuit to access the storing means;
• and
• resuming access to the storing means by the lower-priority image data processing circuit after access to the storing means by the higher-priority image data processing circuit is terminated, and wherein
• a unit operation time period, S1, required for said lower-priority image data processing circuit to process data corresponding to one pixel, a maximum time period, T1, during which the lower-priority image data processing circuit can access the storing means in the unit operation time period, S1, a unit operation time period, S2, required for the higher-priority image data processing circuit to process data corresponding to one pixel and a maximum time period, T2, during which the higher-priority image data processing circuit can access the storing means in the unit operation time period, S2, are determined, so as to satisfy the following conditions:
• S1.gtoreq.T1+T2, and S1.ltoreq.S2.