matlab-call-nidaqmx

matlab-call-nidaqmx

Translate NI-DAQmx C signatures into correct calldaqlib MATLAB calls on Data Acquisition Toolbox R2026a+.

When to Use

• User explicitly mentions calldaqlib or a specific DAQmx* C function
• User needs NI-DAQmx capability the daq object doesn't expose (retriggerable, export signal, reference triggers, enhanced alias rejection, digital filters)
• User is debugging at the driver level (reading back what the NI driver holds)
• User is translating existing C/LabVIEW code to MATLAB

When NOT to Use

• User describes a capability achievable with the daq object alone (dq.Rate, addtrigger, addclock, addinput, read, write, start, stop)
• User asks about the Session-based (legacy) DAQ interface
• User needs DAQmxCreateTask or DAQmxLoadTask (these cannot work through calldaqlib — it owns task creation internally)

Decision Tree

Step 0 — Read the user's intent

Did the user explicitly mention calldaqlib or a specific DAQmx C function?

• Yes — Write the calldaqlib call they asked for. Do NOT redirect to the daq object. They have a reason (driver debugging, matching C code, capability gap, learning). Skip to Step 2.
• No — They described a capability without naming calldaqlib. Go to Step 1.

Step 1 — Pick the right tool

Can the daq object property/method do this? (dq.Rate, addtrigger, addclock, addinput, dq.NumScansAvailable, etc.)

• Yes — Recommend the daq object. Mention calldaqlib only if the user needs driver-level diagnostics or a capability outside daq object coverage.
• No — Proceed to Step 2.

Step 2 — Device-level check

Does the C function lack a taskHandle parameter (device-level API)?

• Functions like DAQmxGetDevIsSimulated, DAQmxGetDevAISupportedMeasTypes: Use an empty daq object (no channels added). Pass the device name as an argument. Returns a plain scalar or array, not a dictionary.
• Functions like DAQmxCreateTask, DAQmxLoadTask: These do not work through calldaqlib at all (calldaqlib owns task creation internally).
• Functions like DAQmxConnectTerms, DAQmxDisconnectTerms: Use an empty daq object (same as device-level queries). These work on X-series devices.

Step 3 — Multi-task check

Does the daq object have multiple internal task handles (e.g., AI + DIO)?

• Getters with a channel arg: The call runs on both tasks. The irrelevant task warns. Read the dictionary key you care about. Acceptable.
• Setters targeting one measurement type: No scoping mechanism. Split into separate daq objects (loses synchronized start/stop).

Step 4 — Buffer placeholder check

Is this a getter returning a string or array?

• String getter (char *data, uInt32 bufferSize in C): Pass "" then bufferSize. Example: calldaqlib(dq, "DAQmxGetSampClkSrc", "", 256)
• Array getter (int32 data[], uInt32 arraySize in C): Pass zeros(1,N,'type') then N. Example: calldaqlib(dq, "DAQmxGetDevAISupportedMeasTypes", "Dev1", zeros(1,32,'int32'), 32)

Step 5 — Enum check

Does any argument correspond to a C int32 enum slot?

• Always use the string form: "DAQmx_Val_RisingSlope" not int32(10280). Both work, but strings are self-documenting and prevent silent wrong-enum bugs.
• See references/enum-constants.md for the 15 most-used enum names.

Call Forms

Six distinct patterns cover all calldaqlib usage:

1. Config (DAQmxCfg*)

dq = daq("ni");
addinput(dq, "Dev1", "ai0", "Voltage");
calldaqlib(dq, "DAQmxCfgSampClkTiming", "/Dev1/PFI0", 5000, ...
    "DAQmx_Val_Rising", "DAQmx_Val_FiniteSamps", uint64(1000));

2. Setter (DAQmxSet*)

calldaqlib(dq, "DAQmxSetStartTrigRetriggerable", true);

3. Getter — scalar (DAQmxGet* returning numeric)

result = calldaqlib(dq, "DAQmxGetSampClkRate");
rate = result("Dev1_ai0");

Returns a dictionary keyed by channel name — even on single-channel objects.

4. Getter — string (DAQmxGet* with char output)

result = calldaqlib(dq, "DAQmxGetSampClkSrc", "", 256);
source = result("Dev1_ai0");

The "" is required as a placeholder for the char *data output slot. bufferSize follows immediately. Use 256 for short names, 1024 for long paths.

5. Getter — array (DAQmxGet* with typed array output)

dEmpty = daq("ni");
result = calldaqlib(dEmpty, "DAQmxGetDevAISupportedMeasTypes", ...
    "Dev1", zeros(1, 32, "int32"), 32);
measTypes = result(result ~= 0);

Pre-allocate a typed buffer (zeros(1,N,'int32')) matching the C signature's array type. Filter unused slots with result(result ~= 0).

6. Device-level (no taskHandle in C signature)

dEmpty = daq("ni");
isSim = calldaqlib(dEmpty, "DAQmxGetDevIsSimulated", "Dev1");

Use an empty daq (no channels added). Pass device name as argument. Returns a plain scalar (not a dictionary).

Also works for terminal routing on X-series devices:

dEmpty = daq("ni");
calldaqlib(dEmpty, "DAQmxConnectTerms", "/Dev1/PFI0", "/Dev1/PFI1", "DAQmx_Val_DoNotInvertPolarity");
calldaqlib(dEmpty, "DAQmxDisconnectTerms", "/Dev1/PFI0", "/Dev1/PFI1");

C-to-calldaqlib Translation

C argument	calldaqlib equivalent
TaskHandle taskHandle	Omit — daq object owns it
const char source[]	MATLAB string "/Dev1/PFI0"
float64 rate	MATLAB double
int32 activeEdge (enum)	Enum name string "DAQmx_Val_Rising"
uInt64 sampsPerChan	uint64(1000)
bool32 data (input)	true / false
float64 *data (output scalar)	Becomes return value (dictionary)
int32 *data (output scalar)	Becomes return value (dictionary)
char *data, uInt32 bufferSize (output pair)	Pass "" + bufferSize
int32 data[], uInt32 arraySize (output array)	Pass zeros(1,N,'int32') + N
Any getter return	Always a dictionary keyed by DevN_chanName

Hard Rules

1. taskHandle is implicit. The daq object owns it. Never pass it.

2. calldaqlib loops over every internal task. A daq with AI + DIO has 2 NI tasks; both get the call. For getters with a channel arg, ignore the warning from the irrelevant task and read the dictionary key you want. For setters targeting one measurement type, split into separate daq objects.

3. Output-pointer args still need a placeholder + bufferSize. String getters: pass "" before bufferSize. Array getters: pass zeros(1,N,'type') before arraySize.

4. start() clobbers calldaqlib-set rate and clock source. start() reapplies dq.Rate to the driver. If you set rate via DAQmxCfgSampClkTiming then call start(), it snaps back to dq.Rate. Fix: set dq.Rate first, use calldaqlib only for parameters the daq object does not track. Alternative: use DAQmxStartTask/DAQmxStopTask via calldaqlib to bypass the daq object's commit pass entirely.

5. Enum constants: use the string form. "DAQmx_Val_RisingSlope" not int32(10280). Strings are readable and prevent wrong-enum bugs. The error on a bad string is misleading ("Value must be of type int32") — it means the string wasn't recognized, not that you should pass an int.

6. Device-level APIs need an empty daq. Functions whose C signature has no taskHandle (like DAQmxGetDevIsSimulated, DAQmxGetDevAISupportedMeasTypes) work only when the daq object has no channels. Create dEmpty = daq("ni") and pass the device name as an arg.

7. DAQmxCreateTask and DAQmxLoadTask cannot work through calldaqlib. These functions create a new task — calldaqlib already owns task creation internally. DAQmxConnectTerms/DAQmxDisconnectTerms DO work via an empty daq object on X-series devices (same pattern as device-level queries).

8. Property values are scalar. Passing a vector where a scalar is expected errors. To set the same property on multiple channels, loop.

9. Channel/device paths are not validated client-side. A bad path produces no error until start().

10. Trigger support is per-device. Not all devices support all trigger types. Error -200077 lists the supported enum values — read it.

11. All task-level getter results return a dictionary. Keyed by DevN_chanName. Never expect a bare scalar. Use result("Dev1_ai0") or iterate keys(result).

12. Buffer-size too small returns NI Error -200228. The error message includes "Required Buffer Size in Bytes: N" — parse it and retry with N. Heuristic: 256 for short names, 1024 for long paths/channel lists.

13. Array getters return a fixed-size buffer. Filter unused trailing zeros with result(result ~= 0).

Conventions

• Always set dq.Rate before using calldaqlib for timing config
• Always use enum name strings, never raw integers
• Always expect a dictionary return from task-level getters
• Always pass "" before bufferSize for string getters
• Always pre-allocate typed buffer for array getters
• Use empty daq (no channels) for device-level queries
• Warn about multi-task semantics in prose before the code block
• Configure trigger type before enabling retriggerable mode
• Retriggerable mode requires DAQmx_Val_FiniteSamps — it does not work with ContSamps
• Use specific getter function names (DAQmxGetSampClkRate) not generic attribute getters (DAQmxGetTimingAttribute)

References

• references/hot-signatures.md — 20 most-used calldaqlib signatures by category
• references/enum-constants.md — 15 DAQmx_Val_* enum name strings
• references/common-mistakes.md — Mistakes from discovery trials and customer usage

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