Quote:
e5frog wrote:
Sounds like it will be expensive, do you have any aim regarding the cost?
Sounds to me a Spartan-3 should be enough. Can't you download an entire VIC-20 emulation in one of those? You'd need to know how of course, don't have those skills myself, made a 8x8 multi color LED battleship game with sampled sound effects some years ago that's about it.
Spartan-3's require a fourth power plane at 2.5V for all the VCCAUX connections. I didn't have enough board room or patience for 4 power planes and another regulator. The cost difference between 3 and 3A isn't too bad and I agree that a Spartan 3A is total overkill but I've looked into other options already.
The cost won't be too bad except for the SRAM, because 32M parallel SRAM's are expensive parts. I could save 90% of the cost of the SRAM by switching to an SDRAM but that adds a lot of complexity because of random access schemes (to interface with the VB) and row/column refreshing and clock generation. Another option is to downgrade the SRAM to 16M. The part I'm using has a pin-compatible 16M version, so I may decide to use 16M to save $10 or so, and then implement the flash save RAM and VBSD menu in the FPGA in memory blocks.
Again, this is a prototype and after I get it working I might decide to switch out the RAM and use a cheaper part to save cost.