This is the IIO driver for AVIA HX711 ADC which is mostly used in weighting
cells.
The protocol is quite simple and using GPIOs:
One GPIO is used as clock (SCK) while another GPIO is read (DOUT)
The raw value read from the chip is delivered.
To get a weight one needs to subtract the zero offset and scale it.
Signed-off-by: Andreas Klinger <ak@xxxxxxxxxxxxx>
---
drivers/iio/adc/Kconfig | 19 ++
drivers/iio/adc/Makefile | 1 +
drivers/iio/adc/hx711.c | 531 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 551 insertions(+)
create mode 100644 drivers/iio/adc/hx711.c
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 932de1f9d1e7..1dcf2ace1697 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -205,6 +205,25 @@ config HI8435
This driver can also be built as a module. If so, the module will be
called hi8435.
+config HX711
+ tristate "AVIA HX711 ADC for weight cells"
+ depends on GPIOLIB
+ help
+ If you say yes here you get support for AVIA HX711 ADC which is used
+ for weigh cells
+
+ This driver uses two GPIOs, one acts as the clock and controls the
+ channel selection and gain, the other one is used for the measurement
+ data
+
+ Currently the raw value is read from the chip and delivered.
+ To get an actual weight one needs to subtract the
+ zero offset and multiply by a scale factor.
+ This should be done in userspace.
+
+ This driver can also be built as a module. If so, the module will be
+ called hx711.
+
config INA2XX_ADC
tristate "Texas Instruments INA2xx Power Monitors IIO driver"
depends on I2C && !SENSORS_INA2XX
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index b1aa456e6af3..d46e289900ef 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -21,6 +21,7 @@ obj-$(CONFIG_CC10001_ADC) += cc10001_adc.o
obj-$(CONFIG_DA9150_GPADC) += da9150-gpadc.o
obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
obj-$(CONFIG_HI8435) += hi8435.o
+obj-$(CONFIG_HX711) += hx711.o
obj-$(CONFIG_IMX7D_ADC) += imx7d_adc.o
obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
new file mode 100644
index 000000000000..e41414556158
--- /dev/null
+++ b/drivers/iio/adc/hx711.c
@@ -0,0 +1,531 @@
+/*
+ * HX711: analog to digital converter for weight sensor module
+ *
+ * Copyright (c) 2016 Andreas Klinger <ak@xxxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/gpio/consumer.h>
+#include <linux/regulator/consumer.h>
+
+/* gain to pulse and scale conversion */
+#define HX711_GAIN_MAX 3
+
+struct hx711_gain_to_scale {
+ int gain;
+ int gain_pulse;
+ int scale;
+ int channel;
+};
+
+/*
+ * .scale depends on AVDD which in turn is known as soon as the regulator
+ * is available
+ * therefore we set .scale in hx711_probe()
+ *
+ * channel A in documentation is channel 0 in source code
+ * channel B in documentation is channel 1 in source code
+ */
+static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {
+ { 128, 1, 0, 0 },
+ { 32, 2, 0, 1 },
+ { 64, 3, 0, 0 }
+};
+
+static int hx711_get_gain_to_pulse(int gain)
+{
+ int i;
+
+ for (i = 0; i < HX711_GAIN_MAX; i++)
+ if (hx711_gain_to_scale[i].gain == gain)
+ return hx711_gain_to_scale[i].gain_pulse;
+ return 1;
+}
+
+static int hx711_get_gain_to_scale(int gain)
+{
+ int i;
+
+ for (i = 0; i < HX711_GAIN_MAX; i++)
+ if (hx711_gain_to_scale[i].gain == gain)
+ return hx711_gain_to_scale[i].scale;
+ return 0;
+}
+
+static int hx711_get_scale_to_gain(int scale)
+{
+ int i;
+
+ for (i = 0; i < HX711_GAIN_MAX; i++)
+ if (hx711_gain_to_scale[i].scale == scale)
+ return hx711_gain_to_scale[i].gain;
+ return -EINVAL;
+}
+
+struct hx711_data {
+ struct device *dev;
+ struct gpio_desc *gpiod_pd_sck;
+ struct gpio_desc *gpiod_dout;
+ struct regulator *reg_avdd;
+ int gain_set; /* gain set on device */
+ int gain_chan_a; /* gain for channel A */
+ struct mutex lock;
+};
+
+static int hx711_cycle(struct hx711_data *hx711_data)
+{
+ int val;
+
+ /*
+ * if preempted for more then 60us while PD_SCK is high:
+ * hx711 is going in reset
+ * ==> measuring is false
+ */
+ preempt_disable();
+ gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
+ val = gpiod_get_value(hx711_data->gpiod_dout);
+ /*
+ * here we are not waiting for 0.2 us as suggested by the datasheet,
+ * because the oszilloscope showed in a test scenario
+ * at least 1.15 us for PD_SCK high (T3 in datasheet)
+ * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz
+ */
+ gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
+ preempt_enable();
+
+ return val;
+}
+
+static int hx711_read(struct hx711_data *hx711_data)
+{
+ int i, ret;
+ int value = 0;
+ int val = gpiod_get_value(hx711_data->gpiod_dout);
+
+ /* we double check if it's really down */
+ if (val)
+ return -EIO;
+
+ for (i = 0; i < 24; i++) {
+ value <<= 1;
+ ret = hx711_cycle(hx711_data);
+ if (ret)
+ value++;
+ }
+
+ value ^= 0x800000;
+
+ for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++)
+ hx711_cycle(hx711_data);
+
+ return value;
+}
+
+static int hx711_wait_for_ready(struct hx711_data *hx711_data)
+{
+ int i, val;
+
+ /*
+ * a maximum reset cycle time of 56 ms was measured.
+ * we round it up to 100 ms
+ */
+ for (i = 0; i < 100; i++) {
+ val = gpiod_get_value(hx711_data->gpiod_dout);
+ if (!val)
+ break;
+ /* sleep at least 1 ms */
+ msleep(1);
+ }
+ if (val)
+ return -EIO;
+
+ return 0;
+}
+
+static int hx711_reset(struct hx711_data *hx711_data)
+{
+ int ret;
+ int val = gpiod_get_value(hx711_data->gpiod_dout);
+
+ if (val) {
+ /*
+ * an examination with the oszilloscope indicated
+ * that the first value read after the reset is not stable
+ * if we reset too short;
+ * the shorter the reset cycle
+ * the less reliable the first value after reset is;
+ * there were no problems encountered with a value
+ * of 10 ms or higher
+ */
+ gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
+ msleep(10);
+ gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
+
+ ret = hx711_wait_for_ready(hx711_data);
+ if (ret)
+ return ret;
+ /*
+ * after a reset the gain is 128 so we do a dummy read
+ * to set the gain for the next read
+ */
+ ret = hx711_read(hx711_data);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * after a dummy read we need to wait vor readiness
+ * for not mixing gain pulses with the clock
+ */
+ ret = hx711_wait_for_ready(hx711_data);
+ if (ret)
+ return ret;
+ }
+
+ return val;
+}
+
+static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
+{
+ int ret;
+
+ if (chan == 0) {
+ if (hx711_data->gain_set == 32) {
+ hx711_data->gain_set = hx711_data->gain_chan_a;
+
+ ret = hx711_read(hx711_data);
+ if (ret < 0)
+ return ret;
+
+ ret = hx711_wait_for_ready(hx711_data);
+ if (ret)
+ return ret;
+ }
+ } else {
+ if (hx711_data->gain_set != 32) {
+ hx711_data->gain_set = 32;
+
+ ret = hx711_read(hx711_data);
+ if (ret < 0)
+ return ret;
+
+ ret = hx711_wait_for_ready(hx711_data);
+ if (ret)
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+static int hx711_read_raw(struct iio_dev *indio_dev,
+ const struct iio_chan_spec *chan,
+ int *val, int *val2, long mask)
+{
+ struct hx711_data *hx711_data = iio_priv(indio_dev);
+ int ret;
+
+ switch (mask) {
+ case IIO_CHAN_INFO_RAW:
+ mutex_lock(&hx711_data->lock);
+
+ /*
+ * hx711_reset() must be called from here
+ * because it could be calling hx711_read() by itself
+ */
+ if (hx711_reset(hx711_data)) {
+ dev_err(hx711_data->dev, "reset failed!");
+ return -EIO;
+ }
+
+ ret = hx711_set_gain_for_channel(hx711_data, chan->channel);
+ if (ret < 0) {
+ mutex_unlock(&hx711_data->lock);
+ return ret;
+ }
+
+ *val = hx711_read(hx711_data);
+
+ mutex_unlock(&hx711_data->lock);
+
+ if (*val < 0)
+ return *val;
+ return IIO_VAL_INT;
+ case IIO_CHAN_INFO_SCALE:
+ *val = 0;
+ mutex_lock(&hx711_data->lock);
+
+ *val2 = hx711_get_gain_to_scale(hx711_data->gain_set);
+
+ mutex_unlock(&hx711_data->lock);
+
+ return IIO_VAL_INT_PLUS_NANO;
+ default:
+ return -EINVAL;
+ }
+}
+
+static int hx711_write_raw(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ int val,
+ int val2,
+ long mask)
+{
+ struct hx711_data *hx711_data = iio_priv(indio_dev);
+ int ret;
+ int gain;
+
+ switch (mask) {
+ case IIO_CHAN_INFO_SCALE:
+ /*
+ * a scale greater than 1 mV per LSB is not possible
+ * with the HX711, therefore val must be 0
+ */
+ if (val != 0)
+ return -EINVAL;
+
+ mutex_lock(&hx711_data->lock);
+
+ gain = hx711_get_scale_to_gain(val2);
+ if (gain < 0) {
+ mutex_unlock(&hx711_data->lock);
+ return gain;
+ }
+
+ if (gain != hx711_data->gain_set) {
+ hx711_data->gain_set = gain;
+ if (gain != 32)
+ hx711_data->gain_chan_a = gain;
+
+ ret = hx711_read(hx711_data);
+ if (ret < 0) {
+ mutex_unlock(&hx711_data->lock);
+ return ret;
+ }
+ }
+
+ mutex_unlock(&hx711_data->lock);
+ return 0;
+ default:
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int hx711_write_raw_get_fmt(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ long mask)
+{
+ return IIO_VAL_INT_PLUS_NANO;
+}
+
+static ssize_t hx711_scale_available_show(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr);
+ int channel = iio_attr->address;
+ int i, len = 0;
+
+ for (i = 0; i < HX711_GAIN_MAX; i++)
+ if (hx711_gain_to_scale[i].channel == channel)
+ len += sprintf(buf + len, "0.%09d ",
+ hx711_gain_to_scale[i].scale);
+
+ len += sprintf(buf + len, "\n");
+
+ return len;
+}
+
+static IIO_DEVICE_ATTR(in_voltage0_scale_available, S_IRUGO,
+ hx711_scale_available_show, NULL, 0);
+
+static IIO_DEVICE_ATTR(in_voltage1_scale_available, S_IRUGO,
+ hx711_scale_available_show, NULL, 1);
+
+static struct attribute *hx711_attributes[] = {
+ &iio_dev_attr_in_voltage0_scale_available.dev_attr.attr,
+ &iio_dev_attr_in_voltage1_scale_available.dev_attr.attr,
+ NULL,
+};
+
+static struct attribute_group hx711_attribute_group = {
+ .attrs = hx711_attributes,
+};
+
+static const struct iio_info hx711_iio_info = {
+ .driver_module = THIS_MODULE,
+ .read_raw = hx711_read_raw,
+ .write_raw = hx711_write_raw,
+ .write_raw_get_fmt = hx711_write_raw_get_fmt,
+ .attrs = &hx711_attribute_group,
+};
+
+static const struct iio_chan_spec hx711_chan_spec[] = {
+ {
+ .type = IIO_VOLTAGE,
+ .channel = 0,
+ .indexed = 1,
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+ },
+ {
+ .type = IIO_VOLTAGE,
+ .channel = 1,
+ .indexed = 1,
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+ },
+};
+
+static int hx711_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct hx711_data *hx711_data;
+ struct iio_dev *indio_dev;
+ int ret;
+ int i;
+
+ indio_dev = devm_iio_device_alloc(dev, sizeof(struct hx711_data));
+ if (!indio_dev) {
+ dev_err(dev, "failed to allocate IIO device\n");
+ return -ENOMEM;
+ }
+
+ hx711_data = iio_priv(indio_dev);
+ hx711_data->dev = dev;
+
+ mutex_init(&hx711_data->lock);
+
+ /*
+ * PD_SCK stands for power down and serial clock input of HX711
+ * in the driver it is an output
+ */
+ hx711_data->gpiod_pd_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
+ if (IS_ERR(hx711_data->gpiod_pd_sck)) {
+ dev_err(dev, "failed to get sck-gpiod: err=%ld\n",
+ PTR_ERR(hx711_data->gpiod_pd_sck));
+ return PTR_ERR(hx711_data->gpiod_pd_sck);
+ }
+
+ /*
+ * DOUT stands for serial data output of HX711
+ * for the driver it is an input
+ */
+ hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_IN);
+ if (IS_ERR(hx711_data->gpiod_dout)) {
+ dev_err(dev, "failed to get dout-gpiod: err=%ld\n",
+ PTR_ERR(hx711_data->gpiod_dout));
+ return PTR_ERR(hx711_data->gpiod_dout);
+ }
+
+ hx711_data->reg_avdd = devm_regulator_get(dev, "avdd");
+ if (IS_ERR(hx711_data->reg_avdd))
+ return PTR_ERR(hx711_data->reg_avdd);
+
+ ret = regulator_enable(hx711_data->reg_avdd);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * with
+ * full scale differential input range: AVDD / GAIN
+ * full scale output data: 2^24
+ * we can say:
+ * AVDD / GAIN = 2^24
+ * therefore:
+ * 1 LSB = AVDD / GAIN / 2^24
+ * AVDD is in uV, but we need 10^-9 mV
+ * approximately to fit into a 32 bit number:
+ * 1 LSB = (AVDD * 100) / GAIN / 1678 [10^-9 mV]
+ */
+ ret = regulator_get_voltage(hx711_data->reg_avdd);
+ if (ret < 0) {
+ regulator_disable(hx711_data->reg_avdd);
+ return ret;
+ }
+ /* we need 10^-9 mV */
+ ret *= 100;
+
+ for (i = 0; i < HX711_GAIN_MAX; i++)
+ hx711_gain_to_scale[i].scale =
+ ret / hx711_gain_to_scale[i].gain / 1678;
+
+ hx711_data->gain_set = 128;
+ hx711_data->gain_chan_a = 128;
+
+ platform_set_drvdata(pdev, indio_dev);
+
+ indio_dev->name = "hx711";
+ indio_dev->dev.parent = &pdev->dev;
+ indio_dev->info = &hx711_iio_info;
+ indio_dev->modes = INDIO_DIRECT_MODE;
+ indio_dev->channels = hx711_chan_spec;
+ indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec);
+
+ ret = iio_device_register(indio_dev);
+ if (ret < 0) {
+ dev_err(dev, "Couldn't register the device\n");
+ regulator_disable(hx711_data->reg_avdd);
+ }
+
+ return ret;
+}
+
+static int hx711_remove(struct platform_device *pdev)
+{
+ struct hx711_data *hx711_data;
+ struct iio_dev *indio_dev;
+
+ indio_dev = platform_get_drvdata(pdev);
+ hx711_data = iio_priv(indio_dev);
+
+ iio_device_unregister(indio_dev);
+
+ regulator_disable(hx711_data->reg_avdd);
+
+ return 0;
+}
+
+static const struct of_device_id of_hx711_match[] = {
+ { .compatible = "avia,hx711", },
+ {},
+};
+
+MODULE_DEVICE_TABLE(of, of_hx711_match);
+
+static struct platform_driver hx711_driver = {
+ .probe = hx711_probe,
+ .remove = hx711_remove,
+ .driver = {
+ .name = "hx711-gpio",
+ .of_match_table = of_hx711_match,
+ },
+};
+
+module_platform_driver(hx711_driver);
+
+MODULE_AUTHOR("Andreas Klinger <ak@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:hx711-gpio");
+
--
2.1.4
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