I'm building a more 'modern' flash cart for the GB. The question is, would you prefer it USB like a Drag'n'Derp? or SD card based like an Everdrive?
SRAM will be 128k to satisfy the LSDJ folk, what is the maximum ROM size you would like it to support?
4Mbytes is the most cost effictive, this would cover 99% of GB/GBC games.
The cart price is targeted at $50 but hopefully strong support will bring the price down.
Let me know your thoughts!
I’ve been looking at how the EZ flash does it, they use a multi layer chip, with 2 Flash layers and one SRAM layer. They come in various capacities with the standard EZ using 32mbytes/32mbytes/32mbytes. This is a huge amount of SRAM and is extremely fast but what is more interesting is the 32byte write time to the Flash being ~30ns!!!!!!!
The problem is I cannot source them throught the regular methods, RS/Mouser/Aliexpress…
Pseudo SRAM as suggested in that thread is BGA and pricey, I don’t mind BGA parts, i haven’t used them but it can’t be too hard. Even if it means making BGA breakout boards to TSOP, its achievable.
What we really need is either a source of the EZ flash chips, or maybe a more modern flash IC with flash write times not stuck in the 1990’s. A 2GB USB stick is cheap enough, I wonder what they use in there for such fast write times. Can even use a CPLD to burst read if we need to.
BennVenn,
Could it be possible to use pseudo SRAM or asynchronous SRAM ? Flash memory is simply too slow and I found a page where creative people are discussing the same issue. More info can be found here:Building an SRAM Substitute
http://www.bigmessowires.com/2015/09/04/building-an-sram-substitute/
Could the suggestions of John Kelley or David be implemented in the upcoming flash cart ?
Keep the scene alive !
Eidis
Eidis,
This kind of feedback is extremely helpful!
I can use the fastest Flash available that will conform to the electrical specs though you’d still expect 30-60seconds to transfer a 1mbyte ROM. The bottle neck is the SD interface + Flash write speed, The cart has access to a 1mhz clock which is a fairly good speed for older SD card compatibility, in bulk read mode this will have 1 byte of data ready for the GB every 8 clock cycles which at the best possible conditions would equal 125kbytes/second. = 8 seconds / Mbyte
There is finite RAM in the GB so we’d be buffering around 2kbytes per transfer, then writing to the Flash ROM in 32byte blocks (most efficient write speed). With the Flash write protocol overhead plus data we’re looking at around 100kbytes/second and that is before you take into account the actual flash write delays.
If we were to use SRAM instead of Flash we’d only have to accept the SD speed limit which would would be great except the price for 32mbits of SRAM is crazy!
its all a balance of cost vs features…
This is exciting to hear! I’d be more than happy with USB or SD. The million dollar question, though, is: Will there be an RTC battery? Fingers crossed!!!
The initial transfer times of the ROM from the SD to the Cart’s internal Flash should be considered very seriously. For example, the Everdrive GB would be perfect if not for the very long erasing and transferring times. I think that your flash cart would be a very huge hit if it could copy any GameBoy ROM to internal flash and launch it under one second. This might sound very demanding, but could prove to be a huge commercial success.
Keep the scene alive!
Eidis