This code is intended to be used to emulate MFM disks using a beaglebone
board with a disk interface daughter card. A makefile is provided to
build mfm_emu. It requires files from the mfm_read/mfm_util programs.

The site for this code is http://www.pdp8online.com/mfm/mfm.shtml

The Makefile assumes am335x_pru_package-master is in the parent directory
of the source. This provides libprussdrv.a for accessing the PRUs, the
PRU assembler, and necessary include files.  The version I used to build it
is at https://github.com/beagleboard/am335x_pru_package. The Debian
distribution includes a version of this package with bugs so for now you
still need to download the current version.

See the pdp8online site above for more information on building.

For emulating disks the code running on PRU 0 is controlled by commands
from the ARM which are documented in cmd.h and prucode0.p. The commands
tell PRU 0 to start processing track data or exit. The emulation uses
track data as MFM clock and data bits. This data is converted to pulse
timing to control a pulse width modulator (PWM) for generating the MFM signal
to the controller. The write data from the controller pulse timing is decoded
and converted back to clock and data bits. This is written in the proper
spot in the emulation data file. The MFM clock and data bits are transferred
in the PRU DDR memory buffer to PRU 1. PRU 1 handles converting the bits
to PWM data and converting the capture time delta data back to MFM bits.
PRU 0 handles actual generation/reading of the MFM signal line and handling
select, head line changes, and seeks. The ARM handles reading and writing
the file and transferring to the DDR memory buffer. It also sends commands
and gets interrupts from PRU 0 to perform the needed operations.
More information is in the headers of the various routines.

See mfm_emu_doc.* for how to run the program.

All the code I created is released under GPLv3 or later.

Source file organization
mfm_emu.c	Top file for reading MFM disks
prucode0.p	The assembly program running in PRU 0
prucode1.p	The assembly program running in PRU 1
cmd.h		The PRU code commands, return status, and various memory
		location definitions
parse_cmdline.c	Routines for parsing and printing the command line options
Makefile	Makefile for building the two executables and PRU code
<other>.h	Various header files which define function prototypes

Other files
setup_emu  Script to configure the beaglebone pins
emu-00A0.dts Device tree file to configure pins

David Gesswein
djg@pdp8online.com