cpu/sam0_common: mitigate rounding errors of SPI baud rate calculation #13537
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Instead of always rounding up, the driver now rounds to the nearest integer. This reduces the absolut rounding error when setting SPI baud rates.
This reverts commit a9faac7. The changed rounding behavior sets the SPI baud rate to 4MHz, which is a suitable rate for the AT86RF212B.
benpicco
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Area: cpu
benpicco
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Mar 3, 2020
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good work! Now we just need an easy EU/USA/CH frequency/page in the Makefile to make it easier to remain legal ;-) |
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Contribution description
After the merge of #13526 @benpicco pointed out that there is room for improvement of the SPI baud rate calculation. This PR implements his proposed formula.
I checked this using a spread sheet. I highlighted cells with a higher frequency than expected resp. desired if the CPU is clocked with 16MHz. Those configurations may cause communication errors since the peripheral may not handle the high SPI clock.
Furthermore, I reverted the commit of #13526. The desired frequency of 5MHz now results into 4MHz, not 8MHz.
Testing procedure
examples/gnrc_networkingshould work of thesamr30-xproboard.Issues/PRs references
#13526