armdsp - a simple framework for developing dsp programs for the TI OMAP

Pace Willisson
pace@alum.mit.edu
July 3, 2010

* Overview

armdsp adds the ability to run bare metal dsp programs on an arm linux
system running on the TI OMAP processor.  The main components are:

armdsp.ko - an arm kernel module for setting up the dsp

rundsp - an arm program for loading a dsp binary into memory, and then
starting the dsp

armhost - an arm program that communicates with the dsp through shared
memory and provides debug printouts

The directory example/ shows how your dsp application will be structured.

* Prerequisites

Board: tested with Zoom OMAP-L138 EVM and the Hawkboard

Host system: Ubuntu 9.10 or similar

TI DSP compiler (cl6x, etc)

ARM compiler (arm-none-linux-gnueabi-gcc, etc)

ARM kernel, configured and compiled

32 megabytes of free DDR memory on the OMAP in the range
0xc4000000...0xc8000000.  You can do this on a 64 megabyte board by
telling linux to use only the first 32 megabytes

4k bytes of free shared ram at 0x80000000 on the OMAP

* Configuration

There's no auto configuration yet. In the mean time, edit the following
variables by hand.  They appear in Makefile, example/Makefile and the
script armdsp-link

** KERNELDIR /opt/hawkboard/linux-omapl1 or /opt/ti/linux-03.20.00.11/

** ARMDSP_DIR /usr/local/armdsp

** ARMDSP_NFSROOT default /arm

ARMDSP_NFSROOT is optional, and is used in "make test" to put files
where the arm can get at them.

* Compilation

	host$ make
	host# make install

* Testing

Send the files to the arm with:

	host$ make test

Log into the arm with two windows.  In the first run:

	arm# armdsp-ldmod
	arm# armhost
	
armhost is now waiting for messages from the dsp, and will print them
out on the armhost standard output.

In the other window, run:

	arm# rundsp dsptest.dsp
	(the dsp will be started, and a message will be printed in the
	armhost window)

Your normal development cycle will be to leave armhost running while
you update your application and execute "rundsp" to start each new
version.

* Theory of operation

armdsp uses two areas of memory:

1. the fist page of the shared memory (address 0x80000000)

2. 32 megabytes of DDR ram (address 0xc4000000)

The first 512 bytes of the shared memory page is used for the dsp
interrupt vector table.  The dsp will start executing from the start
of this table when it comes out of reset.

The dsp program is loaded in the lower part of the DDR ram, and the
dsp stack is set to the top.

The middle of the shared memory page is used to support the TI C
runtime library functions with names such as HOSTwrite, etc, and which
implement simple file-like io.  These functions are normally used with
a jtag emulator to transfer messages between the dsp and to the host
development system.  The TI library is nicely designed, so that simply
defining the functions writemsg and readmsg in the dsp application
allows the same mechanism to be used to communicate through shared
memory with the "armhost" program

The protocol is adequate for debug messages, but you'll need to
implement something custom with other areas of shared memory for a
real application.