Hi, I am using Xilinx FPGAs (Spartan 3E, Spartan 6) and they don't have ROMs. They load the configuration from an external flash chip at power on. I don't see any problem with using RAM for ROM content. The Papilio Pro board has 8Mbyte SDRAM which is way much more than we need in a 8 bit computer. My sdram controller uses half of it for RAM the other half for ROM. ROM is writeable only for the bootstrap logic, TED anyway doesn't assert cs0 or cs1 when a write happens to a ROM address so the Plus4 will never write to it. The Papilio Pro's board has larger SPI flash chip than Spartan 6 needs for its config thus after the FPGA code user data can be stored. I am storing ROM images there and the bootstrap part uploads it to sdram at startup (in theory I could use the flash chip on the fly for ROM reading but I don't like that solution). The FPGA internal RAM I am going to use for a scandoubler. It is static ram and fast. Regards Istvan -----Original Message----- From: Michał Pleban Sent: Sunday, January 01, 2017 11:50 PM To: firstname.lastname@example.org Subject: Re: Switchless ROMs Hello! Hegedűs István wrote: > The FPGA doesn't have much RAM so there is no point in using it to store > ROM images. But ROM and RAM on FPGA are different things. You should not, of course, use RAM to hold ROM contents, but it should be perfectly OK to use ROM to hold ROM contents. I don't know what kind of FPGA you are using, but for example Altera 10M02 has 12 kB of RAM and separate 12 kB of ROM, which is most likely too small for your purposes, but bigger chips have more. Regards, Michau. Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2017-01-03 17:00:02
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