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tcpm: fusb302: Round VNC and Rd thresholds to nearest step

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fusb302 determines attach / no-attach (and Rd / Ra) by comparing CC
voltage against an MDAC output (42 mV steps). The previous 'floor'
calculation was particularly bad for 3.0A Rp (2600 / 42 = 61, 61 * 42 =
2562 mV - 21 = 2551 mV actual threshold, ignoring other error sources).
Reduce the chance of error by rounding our thresholds, which also
matches the suggested thresholds in the datasheet.

BUG=chromium:758608
BRANCH=gru
TEST=Attach problematic dingdong, verify we don't enter an attach /
detach loop.

Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Change-Id: I9211782da0fdad8339246e272952ba1930b69851
Reviewed-on: https://chromium-review.googlesource.com/633276
Reviewed-by: Joe Bauman <joe.bauman@fairchildsemi.com>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit 311b3e4e15fd37ea2ab151edb8b8a468e93355fd)
Reviewed-on: https://chromium-review.googlesource.com/638694
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>
This commit is contained in:
Shawn Nematbakhsh
2017-08-24 08:57:42 -07:00
committed by chrome-bot
parent 88abd3ee72
commit 4e46386877
1 changed files with 6 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
driver/tcpm/fusb302.h
View File

@@ -50,7 +50,12 @@
#define TCPC_REG_MEASURE 0x04
#define TCPC_REG_MEASURE_VBUS (1<<6)
#define TCPC_REG_MEASURE_MDAC_MV(mv) (((mv)/42) & 0x3f)
/*
* MDAC reference voltage step size is 42 mV. Round our thresholds to reduce
* maximum error, which also matches suggested thresholds in datasheet
* (Table 3. Host Interrupt Summary).
*/
#define TCPC_REG_MEASURE_MDAC_MV(mv) (DIV_ROUND_NEAREST((mv), 42) & 0x3f)
#define TCPC_REG_CONTROL0 0x06
#define TCPC_REG_CONTROL0_TX_FLUSH (1<<6)