[Oberon] SD Card File Exchange (was: Why is RSC string data word-aligned?)

[Skulski, Wojciech]

Chris:

>"HCFiler - An efficient embedded SDHC FileSystem"
>https://www.astrobe.com/forum/viewtopic.php?f=4&t=534

I know. It is great!

>Copying files from Windows using HCFiler has not been a high priority for me
>as nobody apart from you has asked me for it to date. Is there anybody else
>here who is interested?

I would ask an opposite question. Why the RISC5 OS should not adopt the HCFiler as an official file system?

>Point me to documentation on how to access SDHC cards using QSPI and I'll
>look into it. I was only aware of MMC as a faster access method. If anybody
>has any experience of using MMC with RISC5 I'd be very interested.

The SD card can be accessed either over SPI or in SD mode, which I named QSPI. The official name is "SD" rather than QSPI. These two are almost the same, but QSPI refers to flash chip access, while SD refers to SD card in QSPI mode. Oh, my.  It could be simpler...

I found some projects. The first two below are pretty well documented. There are official SD documents (short versions) in the github trees. 

1)  http://opencores.org/project,sd_card_controller   in Verilog & VHDL
   In trunk -> doc -> References they provide 
   "Physical Layer Simplified Specification Version 4.10" (2013)
   The VHDL code seems quite different from the Verilog code.

2) http://opencores.org/project,sdcard_mass_storage_controller
   In trunk -> doc -> References they provide 
   Physical Layer Simplified Specification Version 2.00  (2006)
  This is an earlier version of (1).
  It provides two controllers, one simple and one complex but of higher performance.

3) On the XESS Corporation github there is a library of VHDL modules. The SDcard.vhd is among them. This module is documented in source, but there is no separate document. They recommend documentation (4) below. It is using SPI. The commands and other logic are wrapped into VHDL. 

https://github.com/xesscorp/VHDL_Lib
https://raw.githubusercontent.com/xesscorp/VHDL_Lib/master/SDCard.vhd

4) The XESS author recommends the following website. It is pretty comprehensive, with scope screens, some file system discussions, etc.
   http://elm-chan.org/docs/mmc/mmc_e.html 

W.