Using NI example code, I am able to synchronize reading succesive NI analog input blocks with writing a buffer to NI analog outputs starting at the same sample. One additional thing that I need is that once the input and output are underway I want to be able to modify the output buffer being sent to the NI USB-6221 while retaining the sychronization of the input and output.
Is this possible?
Here is the startup code to give an idea of what I'm doing:
...
// Set up input task
DAQmxErrChk (DAQmxCreateTask("", &m_NIUSBXInputTaskHandle));
DAQmxErrChk (DAQmxCreateAIVoltageChan(m_NIUSBXInputTaskHandle, (LPCSTR)GetDeviceInputName(0), "", DAQmx_Val_RSE,
-10.0, 10.0, DAQmx_Val_Volts, NULL));
DAQmxErrChk (DAQmxCreateAIVoltageChan(m_NIUSBXInputTaskHandle, (LPCSTR)GetDeviceInputName(1), "", DAQmx_Val_RSE,
-10.0, 10.0, DAQmx_Val_Volts, NULL));
DAQmxErrChk (DAQmxCfgSampClkTiming(m_NIUSBXInputTaskHandle, NULL, PER_CHANNEL_SAMPLE_RATE,
DAQmx_Val_Rising, DAQmx_Val_ContSamps, (uInt64)PER_CHANNEL_SAMPLE_RATE ));
DAQmxErrChk (GetTerminalNameWithDevPrefix(m_NIUSBXInputTaskHandle, "ai/StartTrigger", TriggerName));
DAQmxErrChk (DAQmxRegisterEveryNSamplesEvent(m_NIUSBXInputTaskHandle, DAQmx_Val_Acquired_Into_Buffer,SAMPLES_PER_BLOCK,
0,BufferedReadEveryNCallback,this));
// Set up output task
DAQmxErrChk (DAQmxCreateTask("",&m_NIUSBXOutputTaskHandle));
DAQmxErrChk (DAQmxCreateAOVoltageChan(m_NIUSBXOutputTaskHandle,GetDeviceOutputName(0),"",
-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCreateAOVoltageChan(m_NIUSBXOutputTaskHandle,GetDeviceOutputName(1),"",
-10.0,10.0,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxCfgOutputBuffer(m_NIUSBXOutputTaskHandle, OUTPUT_BUFFER_SIZE));
DAQmxErrChk (DAQmxCfgSampClkTiming(m_NIUSBXOutputTaskHandle,"",PER_CHANNEL_SAMPLE_RATE,
DAQmx_Val_Rising,DAQmx_Val_ContSamps,(uInt64)PER_CHANNEL_SAMPLE_RATE ));
DAQmxErrChk (DAQmxCfgDigEdgeStartTrig(m_NIUSBXOutputTaskHandle, TriggerName, DAQmx_Val_Rising));
// Set all buffer values to zero initially.
// NOTE: This is the buffer I would like to update...either from an NI callback or I can do it from a
// separate Windows thread I'm running.
for ( int i = 0; i < OUTPUT_BUFFER_SIZE; i++ )
m_NIOutputBuffer[i] = 0;
DAQmxErrChk (DAQmxWriteAnalogF64(m_NIUSBXOutputTaskHandle, SAMPLES_PER_BLOCK, FALSE,
DAQmx_Val_WaitInfinitely, DAQmx_Val_GroupByChannel,
m_NIOutputBuffer, NULL, NULL));
DAQmxErrChk (DAQmxStartTask(m_NIUSBXOutputTaskHandle));
DAQmxErrChk (DAQmxStartTask(m_NIUSBXInputTaskHandle));
--
Dr. Brian Turnquist
Professor, Chair
Bethel University
Mathematics and Computer Science
St Paul, Minnesota 55112
