SAI with MCLK oversampling of 128fs and 64fs

[MOlbr]

Hey guys,

just playing here with the STM32H743 and it's SAI interaces. Works as expected, but from the datasheet the only supported oversampling factors for MCLK are 256 and 512. Especially for higher samplerates with high quality ADC thoose oversampling rates are not typical. 128fs or 64fs are typical for FS=192kHz, So my simple question is: is there an undocumented register entry to set the SAI to 64fs and/or 128fs ? Or do I need to dived MCLK externally by additional hardware?

Btt. HAL is setting bit 27 in ACR1/BCR1 registers, which is not documented. What does it do?

Best regards from Berlin/Germany

Michael

[waclawek.jan]

Hi Michael,

> only supported oversampling factors for MCLK are 256 and 512.

Yes that appears to be a design decision/constraint. As a workaround, try generating MCLK using an other SAI block/module, or any other suitable peripheral clocked from the same primary clock.

> Btt. HAL is setting bit 27 in ACR1/BCR1 registers, which is not documented.

> What does it do?

Good question. Please start a new thread with it to increase chance of ST noticing it.

JW