For the record, there is an Application Note about PDM in ST's STM32F4 page:
AN3998: PDM audio software decoding on STM32 microcontrollers
(pdf<http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/APPLICATION_NOTE/DM00040808.pdf>
)
This is exactly about the MEMs mic on the STM32F4 Discovery board and how
to convert it to 16-bit PCM. From the introduction:
This application note presents the algorithms and architecture of an
optimized software implementation for PDM signal decoding and audio signal
reconstruction when connecting an ST MP45DT02 MEMS microphone with an STM32
microcontroller. It can directly take the Pulse Density Modulated (PDM)
data output from the microphone and convert it to 16-bit pulse-code
modulation (PCM) format.
This document also provides quick start information describing how to
implement the PDM Library for single microphone acquisition via I2S based
on the STM32F4 microcontroller and STM32F4DISCOVERY board.
*Ronan Paixão***
2011/11/3 Peter Lawrence <[email protected]>
> On Thu, Nov 3, 2011 at 4:42 PM, <[email protected]> wrote:
> > MEMs microphone is always going to be pretty crap, couldn't make out
> > whether it has 2 I2S ports...
>
> There are a total of three SPI peripherals (which can operate in an I2S
> mode).
>
> On the STM32F4DISCOVERY board: SPI1 maps to the MEMS accelerometer;
> SPI2 maps to the digital MEMS microphone; SPI3 maps to the headphone
> DAC/amp.
>
> > It does USB host, so perhaps a demo could use a USB headset.
>
> Yes, it is technically feasible that a USB headset could be used, but
> there is no driver code to leverage. When one buys a shrink-wrapped
> USB headset, there is a lot of behind the scenes development to write
> accompanying drivers (primarily for Windows/MacOS). Ostensibly, it
> might conform to a documented "USB class", but the devil is in the
> details.
>
>
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