Cypress's PSoC USB audio solution supports interfacing with an external PDM MEMS microphone. This solution provides a single chip audio path implementation for converting 1-bit PDM input signal to PCM signal (which includes PDM clock generation, PDM Data sampling, DMA data transfer, integrator, decimator and droop correction filtering) and transfer the resultant PCM samples over USB audio class interface to a USB host device.
This audio path implementation uses PSoC's UDB and DMA engine to process and transfer the microphone data, minimizing the CPU overhead and providing a high quality low power PDM microphone interface.
For more details on implementation, see this article: http://edn.com/design/consumer/4425878/High-quality-PDM-microphone-interfacing-using-off-the-shelf-SoCs
The PSoC Creator firmware project is available here: http://www.element14.com/community/thread/28830/l/psoc-4-pioneer-kit-community-project102-usb-audio-using-the-psoc-5lp