stm Posted April 13, 2015 Report Share Posted April 13, 2015 Hi, I wonder how the access to the on-board RAM can be implemented and organized. So far I know that a ZPUino uses the on-board RAM to store programs and data. If I understand it correctly, the ZPUino implementation uses the sram_ctl8.vhd source to access the RAM chip via a Wishbone bus interface. I want to use the Papilio DUO to simulate an expansion board for an old 6502-based computer (Ohio Scientific Challenger 1P). On the one hand I want to use a part of the Papilio DUO RAM chip as a memory expansion for the 6502 board. On the other hand a floppy controller with attached floppy disks shall be simulated with storage on an SD card. So for the RAM expansion alone I only need to translate the 6502 bus to something that can communicate with the Papilio DUO's RAM chip. I either could create a Wishbone bus wrapper around the 6502 bus, and use the sram_ctl8.vhd as-is, or I could directly build a bridge from the 6502 bus to the RAM chip based on the internals of the sram_ctl8.vhd source. But when the floppy controller comes into the picture it gets more complicated. I need to simulate some of the chips for the floppy controller (6850 ACIA and 6820 PIA) and map them into the address space of the 6502. For access to an SD card I will either need to use a ZPUino or the real ATmega32U4 processor. With a ZPuino I would need to divide the RAM between the memory expansion and the ZPUino. So lots of questions arise: How can I divide the RAM between the ZPUino and other parts of my design? Could that be managed with compile and link time options when building the sketch for the ZPUino, or would I need to build something in VHDL? Is it even possible at all to influence the ZPUino's use of the RAM chip without modifying its implementation? Would it be better to use the ATmega32U4 for implementing the access to the SD card? I'm obviously at the very beginner level regarding designing and implementing such a project, so I would be very grateful about any tips and experiences in this area. ThanksStephan Quote Link to comment Share on other sites More sharing options...
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