Retromaster’s Electronics Projects

…related to old computers and other assorted stuff…

UFE SD Card Access Working

Posted by retromaster on May 3, 2010

I’ve managed to get the SD card access working with the new UFE board. It was a mostly straightforward port from the TFE firmware, except for changing a few bits here and there related to the underlying SPI module usage. I have not implemented DMA yet, but I do not think that is going to be a big deal.

It is probably not clear from the photo above, but I also fixed the video flickering issue I mentioned in my previous post. It turns out that the SPI clock is free-running and SPI output gets synchronized to that clock and that made the video output start a pixel late sometimes. Reinitializing the SPI module on each video line did the trick. I chose to have 72 text columns per line this time, as that seems to be achieve a good balance between readability and amount of text shown, at least on my screen. I also implemented DMA for video output, lowering the CPU load. The CPU is not completely freed of video generation tasks however as it needs to prepare the data for the next line while DMA is outputting the current line.

Getting those out of the way, I’ve spent most of the weekend on getting the SDRAM to work. Unfortunately, I haven’t had any success. There are still a few things I would like to try with the software, before I take the drastic step of replacing the chip itself. I desoldered the chip from a SDRAM module that I know to be working beforehand. I might try soldering the chip back to the module just to try if it would still work on a PC. This way I would know at least if the chip is still intact.

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