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preenfm2 and preenfm3 / Stm32F4Discovery port
« on: June 26, 2014, 11:10:19 AM »
Hi,
First of all thank you Xavier for this wonderful project and making it open source.
I've started to port the project to the STM32F4Discovery board, which has a nice audio codec on board. I haven't built the control surface yet, but in the current state I'm able to play notes from USB midi. The board have enough free IO pins left to direct connect the CS buttons and enc-s, so I'll try to eliminate the cs s/p converters too.
To use the onboard I2S audio codec I changed the Systic interrupt to DMA int. Currently I'm using 32 samples long DMA buffer, and it works perfectly. In that way the DMA int is fired only at every 16th sample.
I'm wondering if I can use the full 24 bit resolution of the codec. As far as I see the sample block contains 18 bit normalized uint samples, but I couldn't find where it is normalized. I plan to change the timbre summing at the end of the buildNewSampleBlock(), but I'm sure that it has a better place for it.
Would You mind helping me with the place of the "float to 18 bit" normalizing?
Thank's a lot,
Norbert
First of all thank you Xavier for this wonderful project and making it open source.
I've started to port the project to the STM32F4Discovery board, which has a nice audio codec on board. I haven't built the control surface yet, but in the current state I'm able to play notes from USB midi. The board have enough free IO pins left to direct connect the CS buttons and enc-s, so I'll try to eliminate the cs s/p converters too.
To use the onboard I2S audio codec I changed the Systic interrupt to DMA int. Currently I'm using 32 samples long DMA buffer, and it works perfectly. In that way the DMA int is fired only at every 16th sample.
I'm wondering if I can use the full 24 bit resolution of the codec. As far as I see the sample block contains 18 bit normalized uint samples, but I couldn't find where it is normalized. I plan to change the timbre summing at the end of the buildNewSampleBlock(), but I'm sure that it has a better place for it.
Would You mind helping me with the place of the "float to 18 bit" normalizing?
Thank's a lot,
Norbert