Apparatus for performing direct memory access with stride

A direct memory access controller for controlling a linearly organized memory, the memory storing information for adjacent pixels in sequential addresses, the direct memory access controller comprising;

• a) means for storing an address to which information is to be written or from which information is to be read;
• b) means for storing a value indicative of a width of a block of data to be transferred;
• c) means for storing a value indicating a number of addresses to be bypassed during a transfer;
• d) means for incrementing the address while decrementing the value indicative of the width of the block until the width of the block has been crossed, the means for incrementing the address including;
• 1) a first adder having an input coupled to an output of the means for storing an address and the first adder having an output coupled to an input of the means for storing an address;
• 2) a first subcontractor having an input coupled to the means for storing a value indicative of a width and an output coupled to the means for storing a value indicative of a width;
• and
• 3) a comparator having an input coupled to the output of the first subtractor and the comparator having an output indicative of when the width of the block has been crossed;
• e) means for changing the address by the value indicating a number of addresses to be bypassed during a transfer when the width of the block has been crossed;
• and
• f) means for resetting the value indicative of a width of a block of data to be transferred to the original value when the width of the block has been crossed, the means for resetting including;
• 1) a multiplexor having a first input coupled to an output of the subcontractor and the multiplexor having a second input coupled to the means for storing a value indicating a number of addresses to be bypassed during a transfer, the multiplexor selecting as an output the second input when the width of the block has been crossed;
• and
• 2) a width count register having an input coupled to the output of the multiplexor and having an output connected to the input of the first subcontractor.

A direct memory access controller for transferring a rectangular block of data to and from a linearly organized memory, the memory storing information for adjacent pixels in sequential addresses, the direct access memory controller comprising:

• a) an address pointer register for storing an address to which information is to be written or from which information is to be read;
• b) a width register for storing a value indicative of a width of a block of data to be transferred;
• c) a width count register having an input coupled to the width register;
• d) a stride register for storing a stride value indicating a number of addresses to be bypassed during a transfer;
• e) a length register for storing a value indicating a total amount of information to be transferred;
• f) a first adder for incrementing the address pointer register until a vale of the width count register indicates that the width of the rectangular block has been crossed;
• g) a first subtractor for decrementing the width count register until a value of the width count register indicates that the width of the rectangular block has been crossed;
• h) a second subtractor for decrementing the length register until a value of the width count register indicates that the width of the rectangular block has been crossed;
• i) a first multiplexor having an input coupled to the stride register and an output coupled to the first adder, the first multiplexor selecting the value of the stride register as the output when the width count register indicates that the width of the rectangular block has been crossed;
• and
• j) a second multiplexor having an first input coupled to the width register, a second input coupled to an output of the first subtractor, and an output coupled to the width count register, the second multiplexor resetting the width count register to the value stored by the with register when the width of the block has been crossed.