Per datasheet, SHT4x may need up to 8.2ms for a "high repeatability"
measurement to complete. Attempting to read the result too early
triggers a NAK which then causes an EREMOTEIO error.
This behavior has been confirmed with a logic analyzer while running
the I2C bus at only 40kHz. The low frequency precludes any
signal-integrity issues, which was also confirmed by the absence of
any CRC8 errors. In this configuration, a NAK occurred on any read
that followed the measurement command within less than 8.2ms.
Signed-off-by: David Mosberger-Tang <davidm@xxxxxxxxxx>
---
drivers/hwmon/sht4x.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
index 09c2a0b06444..3415d7a0e0fc 100644
--- a/drivers/hwmon/sht4x.c
+++ b/drivers/hwmon/sht4x.c
@@ -23,7 +23,7 @@
/*
* I2C command delays (in microseconds)
*/
-#define SHT4X_MEAS_DELAY 1000
+#define SHT4X_MEAS_DELAY_HPM 8200 /* see t_MEAS,h in datasheet */
#define SHT4X_DELAY_EXTRA 10000
/*
@@ -90,7 +90,7 @@ static int sht4x_read_values(struct sht4x_data *data)
if (ret < 0)
goto unlock;
- usleep_range(SHT4X_MEAS_DELAY, SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
+ usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
if (ret != SHT4X_RESPONSE_LENGTH) {
--
2.25.1
