More on SD Card Write Performance
Posted by retromaster on April 5, 2010
Over the weekend I was able to do some more test on SD card write performance. I’ve tested with two cards: A SanDisk Ultra II (Class 4) and a SanDisk Extreme (Class 10!).
Both cards are SDHC cards (4GB in size). So the first thing was to add SDHC support to the TFE+ firmware. After figuring out some of the quirks of the SD protocol, I was able to get it to work (fortunately, there are many open source examples on the net, which made the process much easier). Both cards were much better performers than the cards I’ve tested previously. However, there are still some unpredictable busy periods during write operations (can sometimes be up to 20ms even for the Class 10 card). They are much less in frequency and size, but they are still there, nevertheless. Due to the reasons explained in my previous post, this dictates having enough memory on board if writes are to be supported on the Amiga.
All that said, the class 10 card was able to support continuous operation to a certain degree and TFE+ was able to write several tracks to the card during a disk copy attempt with XCopy. Unfortunately, the track data was not valid as the SPI clock was not synchronized to the edges of the floppy write data. I may try to implement this synchronization and see if the data is recorded correctly. It also seems that some additional circuitry may be needed here, but I am not sure.