deviation in ADC sampling results

[sel-zhu]

Hi!
When I use Oscilloscope to observe some signals, it get right results, like this:

Since I want to collect many signals and save them to my disk, when I use command-line tools or scpi to record the signal, both get some deviation to real signal.
In command-line tool, the operation is

In scpi, the code is from "https://github.com/RedPitaya/RedPitaya/blob/master/Examples/python/acquire_trigger_posedge.py"

import sys
import redpitaya_scpi as scpi
import matplotlib.pyplot as plot

rp_s = scpi.scpi(sys.argv[1])

rp_s.tx_txt('ACQ:RST')
rp_s.tx_txt('ACQ:DATA:FORMAT ASCII')
rp_s.tx_txt('ACQ:DATA:UNITS VOLTS')
rp_s.tx_txt('ACQ:DEC 1')

rp_s.tx_txt('ACQ:START')
rp_s.tx_txt('ACQ:TRIG CH1_PE')

while 1:
    rp_s.tx_txt('ACQ:TRIG:STAT?')
    if rp_s.rx_txt() == 'TD':
        break

while 1:
    rp_s.tx_txt('ACQ:TRIG:FILL?')
    if rp_s.rx_txt() == '1':
        break

rp_s.tx_txt('ACQ:SOUR1:DATA?')
buff_string = rp_s.rx_txt()
buff_string = buff_string.strip('{}\n\r').replace("  ", "").split(',')
buff = list(map(float, buff_string))

plot.plot(buff)
plot.ylabel('Voltage')
plot.show()

Both get the results like this:

Where could the problem be?

[b-swat]

HI.
I can't say that. There's not enough information.

SCPI gives a not quite correct result, since the buffer size is not specified.
The data in the middle is most likely valid, the data on the edges is old.

Check this.
#314

[sel-zhu]

Thanks for your reply.
Actually, I forgot to set the States to RP_HIGH(default RP_LOW), it works after adding the code
rp_AcqSetGain(RP_CH_1, RP_HIGH);
Regards.