Method and apparatus for updating data in ROM using a CAM
View Patent ↗A method for providing field updates through the use of a memory emulation circuit with a content addressable memory (CAM) as the intelligent portion of the emulation circuit's arbiter. CAM circuit 200 is comprised of configurable memory and is initially unprogrammed. Address requests are passed straight through multiplexer 201 to Read Only Memory (ROM) 202 . As a result the data in the data location in ROM 202 that corresponds to the requested address will be output to data bus 205 . If data locations in ROM 202 become defective or contain data that needs to be upgraded the circuit implements a remapping of the data location. CAM circuit 200 is programmed with direct addresses to be replaced in ROM 202 . The direct addresses are paired to emulation addresses of data locations in configurable memory 203 . Upgraded or substitute data is programmed into the configurable memory 203 at the paired emulation address. When address requests are received thereafter, CAM circuit 200 compares the address request to its stored direct addresses. If a match is found the paired emulation address is passed through multiplexer 201 instead of the direct address. As a result, the substitute or upgraded data in configurable memory 203 is output to data bus 205 in place of the old data.
1. A content addressable memory arbiter emulation circuit for providing field upgrade capability to an electronic system:
a content addressable memory circuit having an address in terminal coupled to a request address line routing a direct address, an address out terminal, a match signal line, a set of configurable direct addresses, and a set of emulation addresses; and
a multiplexer having a pass control terminal coupled to said match signal line, a first pass input terminal coupled to said address out terminal, a second pass input terminal coupled to said request address line, and a pass output terminal outputting an access address;
a memory address line coupled to said pass output terminal having a first access connection to a block of memory and a second access connection to a block of configurable memory;
wherein said content addressable memory circuit outputs a match signal on said match signal line and outputs a particular emulation address of said set of emulation addresses corresponding to said direct address on said address out terminal when said direct address is in said set of configurable direct addresses;
wherein said multiplexer outputs said particular emulation address on said pass output terminal as said access address when receiving said match signal on said pass control terminal and outputs said direct address on said pass output terminal as said access address when not receiving said match signal on said pass control terminal; and
wherein said memory address line selects one of replacement data from said block of configurable memory in response to said particular emulation address and original data from said block of memory in response to said direct address depending upon the value of said access address to be passed to an output data line.
2. The content addressable memory arbiter emulation circuit of claim 1 , wherein said block of configurable memory block is SRAM.
3. The content addressable memory arbiter emulation circuit of claim 1 , wherein said block of memory is one of ultraviolet programmable ROM and mask ROM.
4. The content addressable memory arbiter emulation circuit of claim 1 ,
wherein said block of configurable memory and said block of memory use a common address decoding scheme; and
wherein said outputting of said access address is done through a decoding circuit.
5. The content addressable memory arbiter emulation circuit of claim 1 , wherein said set of emulation addresses are non-configurable.
6. The content addressable memory arbiter emulation circuit of claim 1 , wherein said direct address has one of an equivalent width as said particular emulation address and a larger width than said particular emulation address.
7. The content addressable memory arbiter emulation circuit of claim 1 , wherein said replacement data from said block of configurable memory is the same size as said original data from said block of memory being replaced by said replacement data from said block of configurable memory.
8. The contents addressable memory arbiter emulation circuit of claim 1 , wherein said set of configurable direct addresses are stored in one of SRAM and fast access registers.
9. The contents addressable memory arbiter emulation circuit of claim 8 , wherein said set of configurable direct addresses is programmed on power-up by one of on-chip and off-chip NVM.
10. A method for providing field upgrades to an electronic system after manufacture and distribution, comprising the steps of:
programming a block of configurable memory with replacement data to act as an upgrade of data in a memory block;
encoding a content addressable memory with direct addresses and emulation addresses;
receiving a direct address request on a request address line;
comparing said direct address request to said direct addresses encoded in said content addressable memory;
delivering a corresponding emulation address of one of said direct addresses to an address line as an access address if said direct address request is equivalent to said one of said direct addresses, whereby a replacement memory segment of said block of configurable memory is retrieved for said electronic system;
sending said direct address request to said address line as said access address if said direct address request is not equivalent to any of said direct addresses, whereby an original memory segment of said memory block is retrieved for said electronic system.
11. The method of claim 10 , wherein said programming and said encoding are accomplished in a concurrent manner.
12. The method of claim 10 , wherein said programming and said encoding are accomplished in an on-line manner where said programming and said encoding update data that is not currently being accessed by the system.
13. The method of claim 10 , wherein said block of configurable memory and said memory block use a common address decoding scheme; and wherein said comparing, delivering, and sending are conducted by a decoding circuit.
14. The method of claim 10 , wherein said method can be repeated any number of times to provide further upgrades of said electronic system.
15. The method of claim 10 , wherein said direct addresses have one of an equivalent width and a larger width than said emulation addresses.
16. The method of claim 10 , wherein said replacement memory segment is the same size as said original memory segment being upgraded.
17. The method of claim 10 , wherein said encoding said direct addresses is conducted at power-up.
18. The method of claim 17 , wherein said encoding of said direct addresses includes transferring data from a NVM memory to said content addressable memory.