Raspberry PI I2S Bus Test Application
Overview
This test application is intended to present a simple to understand user space test application that can be used to control the output of the Raspberry PI I2S bus.The source is available here:
https://github.com/arisena-com/rpi_src
This is the readme file:
#*****************************************************************************
# Copyright (C) 07 Nov 2014 Simon Derek Hughes
# Raspberry PI I2S Bus Test Application
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
# For more information, contact Simon Hughes at:
# Email: simon.d.hughes@arisena.com
# Address: Arisena, 11 Gough Way, Cambridge, CB3 9LN, UK.
#
#*****************************************************************************
Introduction
============
This test application is intended to present a simple to understand user space
test application that can be used to control the output of the Raspberry PI
I2S bus. See the i2s_test.c comments for detailed explanation.
There are a number of deficiencies with the main source of Raspberry Pi
technical documentation (REF1) with regard to the I2S Bus:
- The PCM/I2S clock registers CM_PCM_CTRL and CM_PCM_DIV are not documented.
- The Clock Manager (CM) clock source oscillator frequencies have not been
documented (as they are selected by the board designer)
- REF1 Sec 6.3 Table 6-32 equation for I2S_BCLK average output frequency
(4th column) incorrectly documents 1024 as the divisor to DIVF rather than
the correct value of 4096. Incorrect values of DIVI and DIVF to achieve
a desired I2S_BCLK bit clock frequency are computed using the documented
equation.
This had lead to a confusing picture. Therefore, the aim of this small test
application project is to:
- provide a stand-alone, simple, working code sample that solves all the
problems as a whole, so you can start using the Raspberry Pi I2S bus as
quickly as possible.
- provide references to documentation errata for the CM_PCM_CTRL and
CM_PCM_DIV configuration registers.
- provide a spreadsheet that shows you how to calculate the correct values
of DIVI and DIVF to achieve the desired PCM_CLK/I2S_BLCK target frequency.
Building the i2s_test Application
=================================
If you have a compiler installed on your RPI, copy file files in the
/app/i2s_test/src
subdirectory to your RPI and type:
make
This will compile the i2s_test binary, which should be run as root.
The project is intended to be built in a cross compile environment. See
/app/setup.sh
for more details about setting up the cross compile environment.
Running the I2S Bus Test Application i2s_test
=============================================
See i2s_test.sh for some example command lines for invoking the test
appplication.
Computing DIVI and DIVF values for I2S_BLCK clock frequency
===========================================================
An .xls spreadsheet is supplied so you can compute the correct values
of DIVI & DIVF for the I2S_BCLK clock frequency required for your
application. See the xls in the i2s_test/docs subdir and the notes
in i2s_test.c
Background
==========
Having read BCM2835-ARM-Peripherals.pdf Sec 6.3 (REF1) I thought I had a
detailed map to guide an I2S 3G/4G/LTE modem interfacing project
and quickly bought a Raspberry PI. But slowly, slowly the documentation
reminded me of the Hunting of the Snark:
He had bought a large map representing the sea,
Without the least vestige of land:
And the crew were much pleased when they found it to be
A map they could all understand.
"What's the good of Mercator's North Poles and Equators,
Tropics, Zones, and Meridian Lines?"
So the Bellman would cry: and the crew would reply
"They are merely conventional signs!
"Other maps are such shapes, with their islands and capes!
But we've got our brave Captain to thank
(So the crew would protest) "that he's bought us the best—
A perfect and absolute blank!"
...
Lewis Carroll
Enjoy the hunt.
References
==========
REF1
BCM2835 ARM Peripherals 6 Feb 2012 Broadcom Europe
BCM2835-ARM-Peripherals.pdf, Section 6.3 General Purpose GPIO Clocks.
Simon Hughes
20141124
# Copyright (C) 07 Nov 2014 Simon Derek Hughes
# Raspberry PI I2S Bus Test Application
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
#
# For more information, contact Simon Hughes at:
# Email: simon.d.hughes@arisena.com
# Address: Arisena, 11 Gough Way, Cambridge, CB3 9LN, UK.
#
#*****************************************************************************
Introduction
============
This test application is intended to present a simple to understand user space
test application that can be used to control the output of the Raspberry PI
I2S bus. See the i2s_test.c comments for detailed explanation.
There are a number of deficiencies with the main source of Raspberry Pi
technical documentation (REF1) with regard to the I2S Bus:
- The PCM/I2S clock registers CM_PCM_CTRL and CM_PCM_DIV are not documented.
- The Clock Manager (CM) clock source oscillator frequencies have not been
documented (as they are selected by the board designer)
- REF1 Sec 6.3 Table 6-32 equation for I2S_BCLK average output frequency
(4th column) incorrectly documents 1024 as the divisor to DIVF rather than
the correct value of 4096. Incorrect values of DIVI and DIVF to achieve
a desired I2S_BCLK bit clock frequency are computed using the documented
equation.
This had lead to a confusing picture. Therefore, the aim of this small test
application project is to:
- provide a stand-alone, simple, working code sample that solves all the
problems as a whole, so you can start using the Raspberry Pi I2S bus as
quickly as possible.
- provide references to documentation errata for the CM_PCM_CTRL and
CM_PCM_DIV configuration registers.
- provide a spreadsheet that shows you how to calculate the correct values
of DIVI and DIVF to achieve the desired PCM_CLK/I2S_BLCK target frequency.
Building the i2s_test Application
=================================
If you have a compiler installed on your RPI, copy file files in the
subdirectory to your RPI and type:
make
This will compile the i2s_test binary, which should be run as root.
The project is intended to be built in a cross compile environment. See
for more details about setting up the cross compile environment.
Running the I2S Bus Test Application i2s_test
=============================================
See i2s_test.sh for some example command lines for invoking the test
appplication.
Computing DIVI and DIVF values for I2S_BLCK clock frequency
===========================================================
An .xls spreadsheet is supplied so you can compute the correct values
of DIVI & DIVF for the I2S_BCLK clock frequency required for your
application. See the xls in the i2s_test/docs subdir and the notes
in i2s_test.c
Background
==========
Having read BCM2835-ARM-Peripherals.pdf Sec 6.3 (REF1) I thought I had a
detailed map to guide an I2S 3G/4G/LTE modem interfacing project
and quickly bought a Raspberry PI. But slowly, slowly the documentation
reminded me of the Hunting of the Snark:
He had bought a large map representing the sea,
Without the least vestige of land:
And the crew were much pleased when they found it to be
A map they could all understand.
"What's the good of Mercator's North Poles and Equators,
Tropics, Zones, and Meridian Lines?"
So the Bellman would cry: and the crew would reply
"They are merely conventional signs!
"Other maps are such shapes, with their islands and capes!
But we've got our brave Captain to thank
(So the crew would protest) "that he's bought us the best—
A perfect and absolute blank!"
...
Lewis Carroll
Enjoy the hunt.
References
==========
REF1
BCM2835 ARM Peripherals 6 Feb 2012 Broadcom Europe
BCM2835-ARM-Peripherals.pdf, Section 6.3 General Purpose GPIO Clocks.
Simon Hughes
20141124
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