JPH04373021A - Rom patch device - Google Patents

Abstract

PURPOSE:To save cost and man-hour for changing a ROM by switching a data bus from the ROM to a patch data storage device while responding to a switching information signal, and transferring these data to a ROM access source. CONSTITUTION:An address to access to a ROM 4 is received by a patch address coincidence detector 3 equipped with a circuit to output a switching information signal 10 for detecting and informing whether an access request is outputted or not. When it is judged that the request address to the ROM access requested from a ROM access source 1 is equal to the TOM patch address, the patch address coincidence detector 3 supplies the switching information signal 10 to a bus switching device 2. This device 2 normally connects a data bus 7 from the ROM 4 to a data bus 6 to the ROM access source 1 and when the switching information signal 10 is received, however, a data bus 8 from a patch data storage device 5 is connected to the data bus 6 so that data changing the contents of the ROM can be supplied to the ROM access source 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ROM patch device used for ROM access.

0002

[Prior Art] Conventionally, when a change occurs in the contents of a ROM, the ROM patching method is to either recreate the ROM, or
A method has been used in which the contents of the ROM are once loaded into the RAM and the ROM contents loaded into the RAM are patched.

0003

[Problem to be solved by the invention] The above-mentioned conventional ROM
The patching method involves replacing the ROM with a re-created ROM, or expanding the ROM contents onto the RAM and applying the patch to the expanded data. However, this method has the disadvantage that it requires processing to expand the ROM contents into RAM.

0004

[Means for Solving the Problems] A ROM patch device of the present invention stores a ROM patch address, detects whether or not an access request has been made to the stored address, and outputs a switching notification signal when detected. A patch address match detection device, a patch data storage device that stores ROM patch data (data with changed ROM contents), and a switching notification that notifies that the patch address match detection device has issued an access request to a patch address. It has a bus switching device that switches the data bus from the ROM to the patch data storage device when a signal is input, and transfers data with changed ROM contents in the patch data storage device to the ROM access source.

[0005]

Embodiments Next, embodiments of the present invention will be explained with reference to the drawings.

Referring to FIG. 1, in one embodiment of the present invention, a ROM access source 1 (for example, a CPU) and a RO
For a ROM data reading system in which M4 is connected to the address bus 9 and data buses 7 and 6, the patch address match detection device 3 and the patch data storage device 5 are connected to the address bus 9, and the data bus 7 and 6
A bus switching device 2 is provided between the two.

The operation of the embodiment shown in FIG. 1 will be explained with reference to the flowchart shown in FIG. is received by patch address matching detection device 3, which includes a circuit that stores switching notification signal 10, detects whether an access request has been issued to the stored address, and, if detected, issues a switching notification signal 10 that notifies the detection. It compares with the ROM patch address held by itself (operation step F1). As a result of this comparison, if it is determined that the request address for the ROM access requested by the ROM access source 1 is equal to the ROM patch address, the patch address matching detection device 3 outputs a switching notification signal 10 to the bus switching device 2. supply The bus switching device 2 normally connects the data bus 7 from the ROM 4.
is connected to the data bus 6 to the ROM access source 1, but when receiving the switching notification signal 10, the data bus 8 from the patch data storage device 5 that stores patch data of the ROM is connected to the data bus 6, The data with changed ROM contents is supplied to the ROM access source 1.

That is, when the bus switching device 2 detects the switching notification signal 10, the bus switching device 2 R transfers the data in the patch data storage device 5 to the address requested by the ROM access source 1.
In order to transfer data to OM access source 1, the bus to be connected to data bus 6 is switched from bus 7 to bus 8, thereby transferring data corresponding to the requested address to ROM access source 1 (operation step F2). ROM access source 1
Address and R for ROM access requested by
If the OM patch addresses are not equal, the patch address matching detection device 3 does not output the switching notification signal 10.
The bus switching device 2 transfers the data 7 in the ROM 4 to the ROM access source 1 without performing bus switching (operation step F3).

[0009]

Effects of the Invention As explained above, the present invention transfers the changed data from the patch data storage device to the ROM access source when accessing changed data in the ROM while directly accessing the ROM. It is possible to save the cost and man-hours of
This has the effect of eliminating the need for expansion processing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the embodiment shown in FIG. 1;

[Explanation of symbols]

1 ROM access source 2 Bus switching device 3 Batch address matching detection device 4 RO
M 5 Patch data storage device 6, 7, 8 Data bus 9 Address bus 10 Switching notification signal

Claims (1)

[Claims] Claim 1: A patch address matching detection device that stores a ROM patch address, detects whether an access request has been made to the stored address, and outputs a switching notification signal when detected; The data bus is switched from the ROM to the patch data storage device in response to the switching notification signal output by the patch data storage device to be stored and the patch address match detection device, and the data stored in the patch data storage device is accessed from the ROM. A ROM patch device comprising: a bus switching device for transferring data to a ROM patch device.