Thread: SD card adapter
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Old 14 September 2014, 19:58   #56
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Join Date: Dec 2013
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Originally Posted by pandy71 View Post
AFAIK Paula is not standard FDD controller - this is plain parallel to serial and seriall to parallel converter with DMA + some features to help deal with things typical for FDD - but data stream decoding is performed in a software way (or by CPU or by blitter).
Paula does not use any type of serial data stream. Just like other disk controllers, it clocks bitcell times that are provided from a floppy drive. This is nothing even close to serial data. Flux to data conversion (MFM or GCR, depending on how you set Paula) is the function of Paula's disk controller. You can see how Paula's disk controller circuitry works by looking up the patent that Commodore had for Paula. There is a PLL, missing clock detector, sync detector, etc. Its a rather complex device, and far more flexible than the WD177x controllers of the same era in that it doesn't frame sectors and can provide raw MFM data. The incoming (and outgoing) data is restricted to the legal MFM or GCR values. Hence, no more than three 0 bits in a row for MFM, you can't use FF (and other illegal values), etc. There are different rules for GCR.

I made dozens of things (disk copiers, device drivers, and utilities) that poked directly at Paula. I also just got done helping MikeJ (FPGA Arcade Replay) with the FPGA implementation of Paula for the Amiga core. I know even the undocumented quirks that Paula's disk controller has.

Last edited by JimDrew; 14 September 2014 at 20:09.
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