linux/drivers/iio/adc/hx711.c
Andreas Klinger 68d8ab3cf1 iio: adc: hx711: optimize performance in read cycle
Set gain in hx711_reset() to its default value after a reset cycle. This
omits one precautionary read cycle, because the read is performed in
hx711_set_gain_for_channel() anyway if gain has changed.

Check for DOUT low and if its high wait some time if it goes down
instead of doing a blind reset cycle when DOUT is not down.

This is a performance optimization which allows to query the sensor with
a higher frequency.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
2019-10-22 12:58:07 +01:00

624 lines
14 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* HX711: analog to digital converter for weight sensor module
*
* Copyright (c) 2016 Andreas Klinger <ak@it-klinger.de>
*/
#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/iio/buffer.h>
#include <linux/iio/trigger_consumer.h>
#include <linux/iio/triggered_buffer.h>
#include <linux/gpio/consumer.h>
#include <linux/regulator/consumer.h>
/* gain to pulse and scale conversion */
#define HX711_GAIN_MAX 3
#define HX711_RESET_GAIN 128
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;
/*
* triggered buffer
* 2x32-bit channel + 64-bit timestamp
*/
u32 buffer[4];
/*
* delay after a rising edge on SCK until the data is ready DOUT
* this is dependent on the hx711 where the datasheet tells a
* maximum value of 100 ns
* but also on potential parasitic capacities on the wiring
*/
u32 data_ready_delay_ns;
u32 clock_frequency;
};
static int hx711_cycle(struct hx711_data *hx711_data)
{
unsigned long flags;
/*
* if preempted for more then 60us while PD_SCK is high:
* hx711 is going in reset
* ==> measuring is false
*/
local_irq_save(flags);
gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
/*
* wait until DOUT is ready
* it turned out that parasitic capacities are extending the time
* until DOUT has reached it's value
*/
ndelay(hx711_data->data_ready_delay_ns);
/*
* here we are not waiting for 0.2 us as suggested by the datasheet,
* because the oscilloscope 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);
local_irq_restore(flags);
/*
* make it a square wave for addressing cases with capacitance on
* PC_SCK
*/
ndelay(hx711_data->data_ready_delay_ns);
/* sample as late as possible */
return gpiod_get_value(hx711_data->gpiod_dout);
}
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;
/*
* in some rare cases the reset takes quite a long time
* especially when the channel is changed.
* Allow up to one second for it
*/
for (i = 0; i < 100; i++) {
val = gpiod_get_value(hx711_data->gpiod_dout);
if (!val)
break;
/* sleep at least 10 ms */
msleep(10);
}
if (val)
return -EIO;
return 0;
}
static int hx711_reset(struct hx711_data *hx711_data)
{
int val = hx711_wait_for_ready(hx711_data);
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);
val = hx711_wait_for_ready(hx711_data);
/* after a reset the gain is 128 */
hx711_data->gain_set = HX711_RESET_GAIN;
}
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_reset_read(struct hx711_data *hx711_data, int chan)
{
int ret;
int val;
/*
* 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);
if (ret < 0)
return ret;
val = hx711_read(hx711_data);
return val;
}
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);
switch (mask) {
case IIO_CHAN_INFO_RAW:
mutex_lock(&hx711_data->lock);
*val = hx711_reset_read(hx711_data, chan->channel);
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 irqreturn_t hx711_trigger(int irq, void *p)
{
struct iio_poll_func *pf = p;
struct iio_dev *indio_dev = pf->indio_dev;
struct hx711_data *hx711_data = iio_priv(indio_dev);
int i, j = 0;
mutex_lock(&hx711_data->lock);
memset(hx711_data->buffer, 0, sizeof(hx711_data->buffer));
for (i = 0; i < indio_dev->masklength; i++) {
if (!test_bit(i, indio_dev->active_scan_mask))
continue;
hx711_data->buffer[j] = hx711_reset_read(hx711_data,
indio_dev->channels[i].channel);
j++;
}
iio_push_to_buffers_with_timestamp(indio_dev, hx711_data->buffer,
pf->timestamp);
mutex_unlock(&hx711_data->lock);
iio_trigger_notify_done(indio_dev->trig);
return IRQ_HANDLED;
}
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 const struct attribute_group hx711_attribute_group = {
.attrs = hx711_attributes,
};
static const struct iio_info hx711_iio_info = {
.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),
.scan_index = 0,
.scan_type = {
.sign = 'u',
.realbits = 24,
.storagebits = 32,
.endianness = IIO_CPU,
},
},
{
.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),
.scan_index = 1,
.scan_type = {
.sign = 'u',
.realbits = 24,
.storagebits = 32,
.endianness = IIO_CPU,
},
},
IIO_CHAN_SOFT_TIMESTAMP(2),
};
static int hx711_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
struct device_node *np = dev->of_node;
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)
goto error_regulator;
/* 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;
hx711_data->clock_frequency = 400000;
ret = of_property_read_u32(np, "clock-frequency",
&hx711_data->clock_frequency);
/*
* datasheet says the high level of PD_SCK has a maximum duration
* of 50 microseconds
*/
if (hx711_data->clock_frequency < 20000) {
dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n");
hx711_data->clock_frequency = 400000;
}
hx711_data->data_ready_delay_ns =
1000000000 / hx711_data->clock_frequency;
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_triggered_buffer_setup(indio_dev, iio_pollfunc_store_time,
hx711_trigger, NULL);
if (ret < 0) {
dev_err(dev, "setup of iio triggered buffer failed\n");
goto error_regulator;
}
ret = iio_device_register(indio_dev);
if (ret < 0) {
dev_err(dev, "Couldn't register the device\n");
goto error_buffer;
}
return 0;
error_buffer:
iio_triggered_buffer_cleanup(indio_dev);
error_regulator:
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);
iio_triggered_buffer_cleanup(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@it-klinger.de>");
MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:hx711-gpio");