Abstract: The present invention relates to the management of caches in a data processing apparatus. An ‘n’-way set-associative cache is disclosed, each way comprises a plurality of cache lines, each of said plurality of cache lines comprising a plurality of data words, each of said plurality of data words having associated therewith a unique address. The unique address includes an address portion. The ‘n’-way set-associative cache comprises a cache memory comprising ‘n’ memory units, each of the ‘n’ memory units having a plurality of entries, respective entries in each of the ‘n’ memory units being associated with the same address portion and being operable to store a data word having that same address portion within its unique address.

Abstract: A valid memory 2 is provided storing valid words 8 with bit positions indicating whether corresponding cache lines within a cache memory 7 store valid data. Flip-flop circuits 4 are provided to indicate whether or not the valid words 8 within the valid memory 2 are themselves valid. The number of valid words 8 corresponding to an individual flip-flop circuit 4 varies in dependence upon the size of the valid memory 2. Thus, for example, a single flip-flop circuit 4 may indicate whether one, two, four or eight valid words 8 from the valid memory 2 are storing valid data depending upon the particular size of the valid memory 2 employed.

Abstract: A valid memory 2 is provided storing valid words 8 with bit positions indicating whether corresponding cache lines within a cache memory 7 store valid data. Flip-flop circuits 4 are provided to indicate whether or not the valid words 8 within the valid memory 2 are themselves valid. The number of valid words 8 corresponding to an individual flip-flop circuit 4 varies in dependence upon the size of the valid memory 2. Thus, for example, a single flip-flop circuit 4 may indicate whether one, two, four or eight valid words 8 from the valid memory 2 are storing valid data depending upon the particular size of the valid memory 2 employed.

Abstract: The data processing apparatus comprises a cache having a plurality of cache lines for storing data values retrieved from a plurality of memory regions, when a data value from a first memory region is stored in the cache and is subsequently updated within the cache by a new data value, the new data value is not transferred to memory until that new data value is removed from the cache. A marker is associated with each cache line and is settable to indicate that the data values stored in the corresponding cache line are from said first memory region. A protection unit for controlling the transfer of data values between the cache and the memory, is arranged, when said data values are to be loaded from the memory into a cache line of the cache, to determine whether said data values are from said first memory region and to cause the marker to be set accordingly.

Abstract: A data processing system is provided having a main processor 4 and a coprocessor 26. When in a debug mode, the main processor 4 and the coprocessor 26 are supplied with different instructions. The coprocessor 26 is supplied with a coprocessor debug data generation instruction (MCR) whilst the main processor 4 is supplied with a main processor data capture instruction (LDR). The coprocessor 26 responds to the MCR instruction by controlling debug data representing state of the data processing apparatus 2 to be placed upon a data bus 24 from where it is read by the main processor 4 under control of the LDR instruction.

Abstract: The present invention relates to a technique for accessing memory units in a data processing apparatus. The data processing apparatus comprises of plurality of memory units for storing data values, a processor core for issuing an access request specifying an access to be made to the memory units in relation to a data value, and a memory controller for performing the access specified by the access request. Attribute generation logic is provided for determining from the access request one or more predetermined attributes verifying which of the memory units should be used when performing the access. However, the memory controller does not wait until such determination has been performed by the attribute generation logic before beginning the access.

Abstract: A connection between a source node and a destination node is automatically routed and switched in a WDM photonic network, on receipt of a connection request. A switching and routing mechanism selects a plurality of valid link paths using a path tree, where invalid branches are eliminated based on constraints received in the connection request, and on a link and path cost functions. A regenerator placement tree is used for determining a plurality of viable regenerator paths for each valid link path. On the regenerator placement tree, non-viable branches are eliminated based on constraints received with the request and on regenerator availability at the intermediate nodes along the respective path, and on the specification of these available regenerators. Next, the switching and routing mechanism assigns a set of wavelengths to each viable regenerator path, and estimates the performance of the path using a Q estimator.

Abstract: A cache memory system 22 is described in which a content addressable memory 24 and a cache RAM memory 28 are provided. Each content addressable storage row has an associated hit line 18 and an access enable line 12. An index decoder 46 is provided for controlling cache replacement and cache maintenance operations. The hit line 18 is used for passing both hit signals to the cache RAM 28 and select signals generated by the index decoder 46. A gate 36 operating under control of a multiplexer controller 44 controls this dual-use of the hit line 18 in dependence upon a selected mode of operation. In some embodiments a fast block transfer may be performed by loading data from a first address A into the cache memory 22. A match for the TAG value of the first address A could then be performed and the corresponding hit signal asserted and latched within a latch 43.

Abstract: A data processing system 2 is provided with a processor core 4 that issues virtual addresses VA that are translated to mapped addresses MA by an address translation circuit 6 based upon a predicted address mapping. The mapped address MA is used for a memory access within a memory system 8. The mapped address MA starts to be used before a mapping validity circuit 6 has determined whether or not the predicted translation was valid. Accordingly, if the predicted address translation turns out to be invalid, then the memory access is aborted. The state of the processor core is preserved either by stretching the processor clock signal or by continuing the processor clock signal and waiting the processor 4. The memory system 8 then restarts the memory access with the correct translated address.

Abstract: An image processing system is described in which a data buffer memory 4 is provided between an image processor 2 and an image frame memory 8. The data buffer memory 4 stores a sub-set of the raster lines stored within the image frame memory 8. This data can be read in either an intra-raster-line mode from adjacent memory cells within a bank or in an inter-raster-line mode from memory cell locations at corresponding positions within different banks. The data may be 8-bit pixel data or 16-bit pixel data. In the case of 8-bit pixel data a single bank contains a full raster line whereas in the case of 16-bit pixel data a single raster line extends over two banks.

Abstract: A cache memory 18 is formed of a content addressable memory 20 and a cache RAM 22. The content addressable memory 20 is divided into two or more sections by an AND gate array 28 that serves to selectively either block or unblock the bit lines 26 that supply an input data word to the bit storage and comparison cells 34 of the content addressable memory 20. The generation of match signals for each section is also selectively blocked by preventing the match signal discharge to ground. The match signals from a blocked section are not passed to the RAM 22. The AND gate array 28 and match signal disable may be controlled by the least significant bit of the input data word, higher order bits of the input data word or may be controlled by a bit selected by program control from among the bits of the input data word.

Abstract: A cache memory circuit 36 is described which has a separate read bus 90 and write bus 98. When a given cache row is selected, then simultaneous read and write operations can take place to different words (W#0, W#1, W#2, W#3) within the cache row using the read bus and the write bus. The cache memory circuit 38 having this configuration is particularly suited for use as a write back cache. When a cache miss occurs causing the need for a cache row to be replaced, then the words are replaced starting with the word to which an attempted access triggered the cache miss and proceeding in ascending address order.

Abstract: A method of and apparatus for toning an exposed electrophotographic member in a camera or other electrostatic imaging device which uses liquid toner comprising toner particles suspended in a dispersant.The method contemplates running the liquid toner into a chamber containing the photoconductive surface of the electrophotographic member and a metal plate parallel with one another and spaced apart as two boundaries of the chamber. During the toning operation, a low d.c. bias is applied across the chamber between the photoconductive surface and the plate of a polarity opposite to that characterizing the latent image such as to repel toner particles from the photoconductive surface, but the voltage of the bias is low enough not to affect increments of the surface which have substantial charge on them. The result is that said increments with very little charge are left with practically no adhering particles.

Abstract: A method for charging an electrophotographic imaging surface includes the steps of reciprocating at least one longitudinally disposed corona electrode along the longitudinal axis and simultaneously applying a corona voltage to the electrode for developing a corona so that a substantially uniform corona charge is applied to the entire electrophotographic imaging surface. An additional step, performed simultaneously with production of the corona and reciprocation of the electrode can be the movement of one of the electrodes or the electrophotographic imaging surface relative to the other. Apparatus employed to perform this method also is disclosed.