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['F446 documentation] SAI clock generator

Question asked by waclawek.jan on Jan 2, 2018
Latest reply on Jan 16, 2018 by waclawek.jan

The SAI clock generator subchapter and related comments throughout the SAI chapter are confusing. A complete rewrite would be beneficial, but I doubt anybody is willing to do that. So let me give a couple of simple suggestions:


- the figure ought to contain the SCK-to-FS divider; and the MCLK-to-SCK divider should indicate that its division rate is 256/FRL+1; such figure then would present a complete clock information (for free protocol setting + master).


In fact, you already have that figure; I don't see why RM contains an inferior and confusing version:


- similarly, the formula for SCK frequency shall read MCLK/(256/(FRL+1)), as the multiplication form confusingly suggests that there is some "multiplier" present; and accompanying text should point out that this strange arrangement is designed so that FS is always MCLK/256. The confusing "In the SAI, the single ratio MCLK/FS = 256 is considered." sentence could then be removed


- the text "In master mode it is mandatory that (FRL[7:0] +1) is equal to a number with a power of 2" should be accompained by pointing out the safeguard mechanism in form of WCKCFG


- MCLK stops to be output when MCKDIV=0 and FRL=255; the RM shall say this either in this subchapter, or at FRL bits description; or maybe both, as it's quite surprising.


- in Configuration register 1 (SAI_ACR1 / SAI_BCR1) , description of MCKDIV contains an incorrect formula (the result is not FSCK_x)