From: Marcus Folkesson <marcus.folkesson@gmail.com>
To: Marcus Folkesson <marcus.folkesson@gmail.com>,
Kent Gustavsson <kent@minoris.se>,
Jonathan Cameron <jic23@kernel.org>,
Lars-Peter Clausen <lars@metafoo.de>,
Rob Herring <robh+dt@kernel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH v6 3/9] iio: adc: mcp3911: use correct formula for AD conversion
Date: Mon, 15 Aug 2022 08:16:19 +0200 [thread overview]
Message-ID: <20220815061625.35568-4-marcus.folkesson@gmail.com> (raw)
In-Reply-To: <20220815061625.35568-1-marcus.folkesson@gmail.com>
The ADC conversion is actually not rail-to-rail but with a factor 1.5.
Make use of this factor when calculating actual voltage.
Fixes: 3a89b289df5d ("iio: adc: add support for mcp3911")
Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
drivers/iio/adc/mcp3911.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/adc/mcp3911.c b/drivers/iio/adc/mcp3911.c
index f8875076ae80..890af7dca62d 100644
--- a/drivers/iio/adc/mcp3911.c
+++ b/drivers/iio/adc/mcp3911.c
@@ -40,8 +40,8 @@
#define MCP3911_CHANNEL(x) (MCP3911_REG_CHANNEL0 + x * 3)
#define MCP3911_OFFCAL(x) (MCP3911_REG_OFFCAL_CH0 + x * 6)
-/* Internal voltage reference in uV */
-#define MCP3911_INT_VREF_UV 1200000
+/* Internal voltage reference in mV */
+#define MCP3911_INT_VREF_MV 1200
#define MCP3911_REG_READ(reg, id) ((((reg) << 1) | ((id) << 5) | (1 << 0)) & 0xff)
#define MCP3911_REG_WRITE(reg, id) ((((reg) << 1) | ((id) << 5) | (0 << 0)) & 0xff)
@@ -139,11 +139,18 @@ static int mcp3911_read_raw(struct iio_dev *indio_dev,
*val = ret / 1000;
} else {
- *val = MCP3911_INT_VREF_UV;
+ *val = MCP3911_INT_VREF_MV;
}
- *val2 = 24;
- ret = IIO_VAL_FRACTIONAL_LOG2;
+ /*
+ * For 24bit Conversion
+ * Raw = ((Voltage)/(Vref) * 2^23 * Gain * 1.5
+ * Voltage = Raw * (Vref)/(2^23 * Gain * 1.5)
+ */
+
+ /* val2 = (2^23 * 1.5) */
+ *val2 = 12582912;
+ ret = IIO_VAL_FRACTIONAL;
break;
}
--
2.37.1
next prev parent reply other threads:[~2022-08-15 6:13 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-15 6:16 [PATCH v6 0/9] Improve MCP3911 driver Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 1/9] iio: adc: mcp3911: make use of the sign bit Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 2/9] iio: adc: mcp3911: correct "microchip,device-addr" property Marcus Folkesson
2022-08-15 6:16 ` Marcus Folkesson [this message]
2022-08-15 6:16 ` [PATCH v6 4/9] iio: adc: mcp3911: use resource-managed version of iio_device_register Marcus Folkesson
2022-08-20 12:41 ` Jonathan Cameron
2022-09-12 11:02 ` Marcus Folkesson
2022-09-19 15:36 ` Jonathan Cameron
2022-09-21 20:13 ` Jonathan Cameron
2022-08-15 6:16 ` [PATCH v6 5/9] iio: adc: mcp3911: add support for buffers Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 6/9] iio: adc: mcp3911: add support for interrupts Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 7/9] dt-bindings: iio: adc: mcp3911: add microchip,data-ready-hiz entry Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 8/9] iio: adc: mcp3911: add support for oversampling ratio Marcus Folkesson
2022-08-15 6:16 ` [PATCH v6 9/9] iio: adc: mcp3911: add support to set PGA Marcus Folkesson
2022-08-16 10:22 ` [PATCH v6 0/9] Improve MCP3911 driver Krzysztof Kozlowski
2022-08-16 14:57 ` Marcus Folkesson
2022-08-17 6:12 ` Krzysztof Kozlowski
2022-08-17 16:08 ` Marcus Folkesson
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