ESP32 Forum

Posted: **Wed Oct 23, 2019 6:39 pm**

My ultimate goal is to do high frequency (100-1000 kHz) ADC in the 0-1.1V range, i.e. with 0dB attenuation. Therefore, I am trying to use the DIG SAR ADC controller which can be accessed through the I2S peripheral, based of this example:https://github.com/espressif/arduino-es ... eq_ADC.ino. The example seems to be working for me, but by default it uses the maximum attenuation setting which yields a voltage range of 0-4V. And unlike the standard way of using the ADC, like this: (which gives me about 20 kHz sampling frequency; somehow even less than analogRead() does ~ 50kHz)

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adc1_config_width(ADC_WIDTH_12Bit);// use the max 12 bit ADC precision
adc1_config_channel_atten(ADC1_GPIO33_CHANNEL,ADC_ATTEN_0db);//strap ADC1 to GPI 33
cx_in[i] = adc1_get_raw(ADC1_GPIO33_CHANNEL);//read a sample

There is no setting as far as I can find which lets me easily adjust it, (using the adc1_config_channel_atten() command does not appear to have an affect on the DIG SAR ADC approach). This is where I started digging into the technical reference manual and stumbled upon this overview:

: DIG_SAR_ADC_Control_Top.PNG (222.43 KiB) Viewed 3861 times

It clearly shows the pattern table which contains the attenuation for up to 16 measurement rules per controller. More detailed:

: apb_registers.PNG (436.17 KiB) Viewed 3861 times

and description of contents per register:

: APB_SARADC_SAR1_PATT_TAB1_REG.PNG (105.72 KiB) Viewed 3861 times

So my idea was to write to this address and use a mask to set the attanuation to 0dB. However, I'm a noob and haven't approached registers on the ESP32 before so I'm quite unsure about what to do. After a lot of googling I think I have to do it like this:

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uint32_t mask = 0xFCFCFCFC;
  *((volatile uint32_t *) (0x0600261C)) &= mask;

However, this causes my board to crash and it ends up in a bootloop.

I was also looking around to find the header files which should contain the register addresses for APB_SARADC_SAR1_PATT_TAB1_REG etc, but I couldn't find this one exactly. I did find APB_CTRL_APB_SARADC_SAR1_PATT_TAB1_REG in <soc/apb_ctrl_reg.h> which points to a different address than the one given in the documentation.

Modifying the address from this header doesn't cause me bootloops but also doesn't seem to affect my attenuation

.

Sorry about the long story, but I would really appreciate it if someone can help me find the right register and tell me how to address it properly.

ESP32 Forum

How to access APB registers for DIG SAR ADC

How to access APB registers for DIG SAR ADC