ADC can’t exceed the maximum sample rate of 50kSa/s using libiio

[Jakub]

Hello,

I am experiencing an issue with a low ADC sample rate when using triggered buffered mode. Although I have set sufficient values in the IIO user space interface, the actual sample rate cannot exceed 50 kSa/s, regardless of what I try. I use Linux 5.15 kirkstone with this device tree:

https://github.com/jromanki/meta-octavo-osd32mp1/blob/kirkstone/recipes-kernel/linux/files/0023-Add-Device-Tree-support-for-OSD32MP1-BRK.patch

And after startup these properties are edited:

echo 0 > /sys/bus/platform/devices/44000000.timer:pwm/pwm/pwmchip10/export
echo 10000 > /sys/bus/platform/devices/44000000.timer:pwm/pwm/pwmchip10/pwm0/period
echo 5000 > /sys/bus/platform/devices/44000000.timer:pwm/pwm/pwmchip10/pwm0/duty_cycle
echo 100000 > /sys/bus/iio/devices/trigger0/sampling_frequency
echo 1 > /sys/bus/platform/devices/44000000.timer:pwm/pwm/pwmchip10/pwm0/enable

echo “tim1_trgo” > /sys/bus/iio/devices/iio\:device1/trigger/current_trigger
echo 1 > /sys/bus/iio/devices/iio\:device1/scan_elements/in_voltage0_en
echo 1 > /sys/bus/iio/devices/iio\:device1/scan_elements/in_voltage1_en

echo 4096 > /sys/bus/iio/devices/iio\:device1/buffer/length
echo 2048 > /sys/bus/iio/devices/iio\:device1/buffer/watermark
echo 1 > /sys/bus/iio/devices/iio\:device1/buffer/enable

Here is my output of the iio_info command:

Library version: 0.23 (git tag: 92d6a35)
Compiled with backends: local xml ip usb serial
IIO context created with local backend.
Backend version: 0.23 (git tag: 92d6a35)
Backend description string: Linux osd32mp1-brk 5.15.24 #1 SMP PREEMPT Wed Feb 16 11:56:41 UTC 2022 armv7l
IIO context has 2 attributes:
local,kernel: 5.15.24
uri: local:
IIO context has 8 devices:
iio:device0: 44000000.timer:timer@0
1 channels found:
count0:  (input)
8 channel-specific attributes found:
attr  0: en value: 1
attr  1: enable_mode value: always
attr  2: enable_mode_available value: always gated triggered
attr  3: preset value: 2087
attr  4: raw value: 831
attr  5: scale value: 1.000000000
attr  6: trigger_mode ERROR: Invalid argument (22)
attr  7: trigger_mode_available value: trigger
ERROR: checking for trigger : Input/output error (5)
iio:device1: 48003000.adc:adc@0 (buffer capable)
2 channels found:
voltage0:  (input, index: 0, format: le:U16/16>>0)
3 channel-specific attributes found:
attr  0: offset value: 0
attr  1: raw ERROR: Device or resource busy (16)
attr  2: scale value: 0.044250488
voltage1:  (input, index: 1, format: le:U16/16>>0)
3 channel-specific attributes found:
attr  0: offset value: 0
attr  1: raw ERROR: Device or resource busy (16)
attr  2: scale value: 0.044250488
2 device-specific attributes found:
attr  0: trigger_polarity value: rising-edge
attr  1: trigger_polarity_available value: rising-edge falling-edge both-edges
2 buffer-specific attributes found:
attr  0: data_available value: 4096
attr  1: watermark value: 2048
7 debug attributes found:
debug attr  0: lincalfact6 value: 509
debug attr  1: lincalfact5 value: 540542463
debug attr  2: lincalfact4 value: 538446337
debug attr  3: lincalfact3 value: 537392635
debug attr  4: lincalfact2 value: 541593087
debug attr  5: lincalfact1 value: 540542465
debug attr  6: direct_reg_access value: 0x100A
Current trigger: trigger0(tim1_trgo)
trigger0: tim1_trgo
0 channels found:
3 device-specific attributes found:
attr  0: master_mode value: update
attr  1: master_mode_available value: reset enable update compare_pulse OC1REF OC2REF OC3REF OC4REF
attr  2: sampling_frequency value: 100037
No trigger on this device
trigger1: tim1_trgo2
0 channels found:
3 device-specific attributes found:
attr  0: master_mode value: reset
attr  1: master_mode_available value: reset enable update compare_pulse OC1REF OC2REF OC3REF OC4REF OC5REF OC6REF compare_pulse_OC4REF compare_pulse_OC6REF compare_pulse_OC4REF_r_or_OC6REF_r compare_pulse_OC4REF_r_or_OC6REF_f compare_pulse_OC5REF_r_or_OC6REF_r compare_pulse_OC5REF_r_or_OC6REF_f
attr  2: sampling_frequency value: 100037
No trigger on this device
trigger2: tim1_ch1
0 channels found:
No trigger on this device
trigger3: tim1_ch2
0 channels found:
No trigger on this device
trigger4: tim1_ch3
0 channels found:
No trigger on this device
trigger5: tim1_ch4
0 channels found:
No trigger on this device

Despite these efforts, the sampling rate still cannot exceed 50 kSa/s when tested with a signal generator. Do you have any suggestions as to why this might be the case? Thanks in advance.

Best Regards,

jromanki

[Author]

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