Add the page on the MX disk format. Mac disks are now unicorns.

README.md

@@ -89,7 +89,7 @@ people who've had it work).
 | [Brother 120kB](doc/disk-brother.md)     |  🦄   |        |                                     |
 | [Brother 240kB](doc/disk-brother.md)     |  🦄   |   🦄   |                                     |
 | [Brother FB-100](doc/disk-fb100.md)      |  🦖   |        | Tandy Model 100, Husky Hunter, knitting machines |
-| [Macintosh 800kB](doc/disk-macintosh.md) |  🦖   |        | and probably the 400kB too          |
+| [Macintosh 800kB](doc/disk-macintosh.md) |  🦄   |        | and probably the 400kB too          |
 | [TRS-80](doc/disk-trs80.md)              |  🦖   |        | a minor variation of the IBM scheme |
 {: .datatable }
 
@@ -105,6 +105,7 @@ at least, check the CRC so what data's there is probably good.
 |:-----------------------------------------|:-----:|:------:|-------|
 | [AES Superplus / No Problem](doc/disk-aeslanier.md) |  🦖   | | hard sectors! |
 | [Durango F85](doc/disk-durangof85.md)    |  🦖   |        | 5.25" |
+| [DVK MX](doc/disk-mx.md)                 |  🦖   |        | Soviet PDP-11 clone |
 | [Victor 9000](doc/disk-victor9k.md)      |  🦖   |        | 8-inch        |
 | [Zilog MCZ](doc/disk-zilogmcz.md)        |  🦖   |        | 8-inch _and_ hard sectors |
 {: .datatable }
@@ -189,7 +190,7 @@ Jonathan Müller (`foonathan <https://github.com/foonathan>`) with
 contributions from many other people. It is licensed under the terms of the
 BSD license. Please see the contents of the directory for the full text.
 
-As an exception, `dep/fnmatchemu` contains parts of the OpenBSD C library
+As an exception, `dep/emu` contains parts of the OpenBSD C library
 code, Todd Miller and William A. Rowe (and probably others). It is licensed
 under the terms of the 3-clause BSD license. Please see the contents of the
 directory for the full text. It's been lightly modified by me.

doc/disk-mx.md

@@ -0,0 +1,65 @@
+Disk: DVK MX
+============
+
+The DVK (in Russian, ДВК, Диалоговый вычислительный комплекс or Dialogue
+Computing Complex) was a late 1970s Soviet personal computer, a cut-down
+version of the professional SM EVM (СМ ЭВМ, abbreviation of Система Малых ЭВМ
+--- literally System of Mini Computers), which _itself_ was an unlicensed
+clone of the PDP-11. The MX board was an early floppy drive controller board
+for it.
+
+<div style="text-align: center">
+<a href="http://www.leningrad.su/museum/show_big.php?n=1006"><img src="dvk3m.jpg" style="max-width: 60%" alt="A Durango F85, held precariously"></a>
+</div>
+
+The MX format is interesting in that it has to be read a track at a time. The
+format contains the usual ID prologue at the beginning of the track, then
+eleven data blocks and checksums, then the epilogue, then it stops. The
+actual encoding is normal FM. There were four different disk variants, in all
+combinations of single- and double-sided and 40- and 80-tracked; but every
+track contained eleven 256-byte sectors.
+
+The format varies subtly depending on whether you're using the 'new' driver
+or the 'old' driver. FluxEngine should read both.
+
+A track is:
+
+  * 8 x 0x0000 words (FM encoded as 01010101...)
+  * 1 x 0x00F3 --- start of track
+  * 1 x 0xnnnn --- track number
+  * 11 of:
+    * 128 words (256 bytes) of data
+    * 16 bit checksum
+  * **if 'new' format:**
+    * 3 x 0x83nn --- `n = (track_number<<1) + side_number`
+  * **if 'old' format:**
+    * 3 x 0x8301
+
+The checksum is just the unsigned integer sum of all the words in the sector.
+Words are all stored little-endian.
+
+Reading discs
+-------------
+
+```
+fluxengine read mx
+```
+
+You should end up with an `mx.img` which will vary in length depending on the format. The default is double-sided 80-track. For the other formats, use:
+
+  * single-sided 40-track: `-s :s=0:t=0-79x2`
+  * double-sided 40-track: `-s :s=0-1:t=0-79x2`
+  * single-sided 40-track: `-s :s=0:t=0-79`
+  * double-sided 40-track: `-s :s=0-1:t=0-79`
+
+
+Useful references
+-----------------
+
+  - [The Soviet Digital Electronics
+    Museum](http://www.leningrad.su/museum/main.php) (source of the image
+    above)
+
+  - [a random post on the HxC2001 support
+    forum](http://torlus.com/floppy/forum/viewtopic.php?t=1384) with lots of
+    information on the format