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cross-platform inconsistency in I2C bus speeds #24067

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pabigot opened this issue Apr 3, 2020 · 2 comments · Fixed by #24159
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cross-platform inconsistency in I2C bus speeds #24067

pabigot opened this issue Apr 3, 2020 · 2 comments · Fixed by #24159
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@MaureenHelm @mnkp
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area: I2C bug The issue is a bug, or the PR is fixing a bug priority: low Low impact/importance bug

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@pabigot
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pabigot commented Apr 3, 2020

The I2C bus specification in section 5 specifies these named speeds:

  • Standard up to 100 kHz
  • Fast up to 400 kHz
  • Fast+ up to 1 MHz
  • High up to 3.4 MHz
  • Ultra up to 5 MHz (unidirectional only)

Evaluation in #23971 (review) plus code review show that NXP (mcux, mcux_lpi2c, imx) and SiLabs (gecko) I2C drivers use 1 MHz for Fast, and do not implement Fast+.

The interpretation of named I2C bus speeds in Zephyr should be (a) documented and (b) consistent.
@pabigot pabigot added the bug The issue is a bug, or the PR is fixing a bug label Apr 3, 2020
@aloeppert aloeppert mentioned this issue Apr 3, 2020
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@carlescufi carlescufi added area: I2C priority: low Low impact/importance bug labels Apr 7, 2020
@carlescufi
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@mnkp and @MaureenHelm could you send a patch to correct Fast so it becomes Fast+?

@MaureenHelm
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@mnkp and @MaureenHelm could you send a patch to correct Fast so it becomes Fast+?

yes

@MaureenHelm MaureenHelm mentioned this issue Apr 7, 2020
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@MaureenHelm MaureenHelm

@mnkp mnkp

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area: I2C bug The issue is a bug, or the PR is fixing a bug priority: low Low impact/importance bug
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drivers: i2c: Fix incorrect fast and fast+ mode bus speeds
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@pabigot @MaureenHelm @carlescufi @mnkp