2.8. ADC

2.8.1. Introduction

ADC (Analog-to-digital Converter) can convert continuous analog signals into discrete digital signals.

The ADC module in BL MCU series has the following characteristics:

• Support selecting 12/14/16 bits conversion result output

• ADC maximum working clock is 2MHZ

• Support 2.0V, 3.2V optional internal reference voltage

• DMA support

• Support four modes: single channel single conversion, continuous single channel conversion, single multi-channel conversion and continuous multi-channel conversion mode

• Support both single-ended and differential input modes

• 12 external analog channels

• 2 DAC internal channels

• 1 VBAT /2 channel

2.8.2. ADC Device Structure Definition

typedef struct adc_device {
    struct device parent;
    adc_clk_div_t clk_div;
    adc_vref_t vref;
    bool continuous_conv_mode;
    bool differential_mode;
    adc_data_width_t data_width;
    adc_fifo_threshold_t fifo_threshold;
    adc_pga_gain_t gain;
} adc_device_t;

• parent inherits the properties of the parent class

• clk_div Partial frequency clock in ADC module

• vref 2.0/3.2V reference voltage optional

• continuous_conv_mode Whether to select continuous mode. If it is in continuous mode, once adc_start operation, ADC will continue to work until adc_stop. If it is not in continuous mode, adc will only convert the result once every adc_start.

• differential_mode Whether it is in differential mode, if it is in differential mode, negative voltage can be measured.

• data_width Measurement width selection, the actual accuracy of ADC is 12 bits, but the accuracy of 14bits / 16bits can be achieved by averaging multiple times through OSR. Note that when a higher data width is selected, the frequency will decrease due to averaging. For details, please refer to the enumeration information.

• fifo_threshold This parameter affects the DMA handling threshold and ADC FIFO interrupt threshold

• gain ADC gain selection for input signal

• Others to be added

2.8.3. ADC Device Parameter Configuration Table

Each ADC has a parameter configuration macro, the macro definition is located in the peripheral_config.h file under the bsp/board/xxx directory, and the variable definition is located in hal_adc.c, so there is no need for the user to define it by himself . When the user opens the macro of the corresponding device, the configuration of the device will take effect. For example, open the macro BSP_USING_ADC0 to take effect, and at the same time, the ADC device can be registered and used.

/*Parameter configuration macro*/
#if defined(BSP_USING_ADC0)
#ifndef ADC0_CONFIG
#define ADC0_CONFIG                                        \
    {                                                      \
        .clk_div = ADC_CLOCK_DIV_32,                       \
        .vref = ADC_VREF_3P2V,                             \
        .continuous_conv_mode = DISABLE,                   \
        .differential_mode = DISABLE,                      \
        .data_width = ADC_DATA_WIDTH_16B_WITH_256_AVERAGE, \
        .fifo_threshold = ADC_FIFO_THRESHOLD_1BYTE,        \
        .gain = ADC_GAIN_1                                 \
    }
#endif
#endif

/*Variable definitions*/
static adc_device_t adcx_device[ADC_MAX_INDEX] = {
#ifdef BSP_USING_ADC0
    ADC0_CONFIG,
#endif
};

备注

The above configuration can be modified through ADC_DEV(dev)->xxx and can only be used before device_open.

2.8.4. ADC Device Interface

ADC device interfaces all follow the interfaces provided by the standard device driver management layer.

2.8.4.1. adc_register

adc_register is used to register an ADC device standard driver interface.Before registering, you need to open the macro definition of the corresponding ADC device. For example, define the macro BSP_USING_ADC0 to use the ADC0 device. After the registration is completed, other interfaces can be used. If no macro is defined, the ADC0 device cannot be used.

int adc_register(enum adc_index_type index, const char *name);

• index device index to be registered

• name device name to be registered

index is used to select ADC device configuration, one index corresponds to one ADC device configuration, for example, ADC0_INDEX corresponds to ADC0_CONFIG configuration. index has the following optional types:

enum adc_index_type
{
#ifdef BSP_USING_ADC0
    ADC0_INDEX,
#endif
    ADC_MAX_INDEX
};

2.8.4.2. device_open

device_open is used to open an ADC device,this funtion calls adc_open actually.

int device_open(struct device *dev, uint16_t oflag);

• dev device handle

• oflag open mode

• return Error code, 0: open successfully, others: error

oflag provides the following types

#define DEVICE_OFLAG_STREAM_TX  0x001 /* The device is turned on in rotation sending mode */
#define DEVICE_OFLAG_STREAM_RX  0x002 /* The device is turned on in rotation receiving mode */
#define DEVICE_OFLAG_INT_TX     0x004 /* The device is turned on in interrupt sending mode */
#define DEVICE_OFLAG_INT_RX     0x008 /* The device is turned on in interrupt receiving mode */
#define DEVICE_OFLAG_DMA_TX     0x010 /* The device is turned on in DMA transmission mode */
#define DEVICE_OFLAG_DMA_RX     0x020 /* The device is turned on in DMA receiving mode */

2.8.4.3. device_close

device_close is used to close an ADC device,this funtion calls adc_close actually.

int device_close(struct device *dev);

• dev device handle

• return Error code, 0: open successfully, others: error

2.8.4.4. device_control

device_control is used to control and modify the parameters of the adc device according to commands.This funtion calls adc_control actually.

int device_control(struct device *dev, int cmd, void *args);

• dev Device handle

• cmd Device control commands

• args Control parameter

• return Different control commands return different meanings.

In addition to standard control commands, serial devices also have their own special control commands.

#define DEVICE_CTRL_ADC_CHANNEL_START  0x10
#define DEVICE_CTRL_ADC_CHANNEL_STOP   0x11
#define DEVICE_CTRL_ADC_CHANNEL_CONFIG 0x12
#define DEVICE_CTRL_ADC_VBAT_ON        0x13
#define DEVICE_CTRL_ADC_VBAT_OFF       0x14
#define DEVICE_CTRL_ADC_TSEN_ON        0x15
#define DEVICE_CTRL_ADC_TSEN_OFF       0x16

args input is different depending on cmd, the list is as follows:

table1

cmd	args	description
DEVICE_CTRL_SET_INT	adc_it_type	Enable ADC device interrupt
DEVICE_CTRL_CLR_INT	adc_it_type	Disable ADC device interrupt
DEVICE_CTRL_CONFIG	ADC_param_cfg_t	Modify ADC configuration
DEVICE_CTRL_ADC_CHANNEL_CONFIG	adc_channel_cfg_t	Modify ADC channel configuration
DEVICE_CTRL_ATTACH_RX_DMA	struct device*	Link receiving DMA device
DEVICE_CTRL_ADC_CHANNEL_START	NULL	Start/continue ADC conversion
DEVICE_CTRL_ADC_CHANNEL_STOP	NULL	Stop ADC conversion
DEVICE_CTRL_ADC_VBAT_ON	NULL	Turn on the internal VDD measurement circuit
DEVICE_CTRL_ADC_VBAT_OFF	NULL	Turn off the internal VDD measurement circuit
DEVICE_CTRL_ADC_TSEN_ON	NULL	Turn on the internal temperature measurement circuit (requires hardware support)
DEVICE_CTRL_ADC_TSEN_OFF	NULL	Turn off the internal temperature measurement circuit (requires hardware support)

2.8.4.5. device_read

device_read is used to receive the data of ADC device, the receiving mode can be polling, interrupt, dma.

int device_read(struct device *dev, uint32_t pos, void *buffer, uint32_t size);

• dev Dvice handle

• pos No effect

• buffer Buffer to read

• size Length to read

• return Error code, 0: open successfully, others: error

2.8.4.6. device_set_callback

device_set_callback is used to register an ADC threshold interrupt callback function.

int device_set_callback(struct device *dev, void (*callback)(struct device *dev, void *args, uint32_t size, uint32_t event));

• dev Device handle

• callback The interrupt callback function to be registered

  • dev Device handle

  • args Receive and send buffer, the data type is uint8_t*

  • size Transmission length

  • event Type of interrupt event

event type is as follows:

enum ADC_event_type
{
    ADC_EVENT_FIFO_READY,
    ADC_EVENT_OVERRUN,
    ADC_EVENT_UNDERRUN,
};