NXT Functions Datalog

NXT → Functions and Variables → Datalog

The NXT has a data logging capability similar to that found in the RCX. This capability allows you to save variable and sensor values in a log during program execution. This is useful for collecting data during measurements. It is also useful for program debugging where you may want to analyze the value of a particular variable after a program has been run. There’s room for storage of about 5,000 data points. The data points are stored into RAM. They can be subsequently copied to a NXT flash file. They are not immediately stored into a flash file during program execution because writing to a file in the flash memory can take 3 to 6 milliseconds which could disturb performance of the user application. There are utilities within the ROBOTC IDE to upload the datalog and display in a PC window. These can be found under the “debug display” and the “NXT -> Files Management” display.

Color Key Function: Variable:

AddToDatalog

void AddToDatalog(const long data)

(void) Adds an entry to the datalog.

Parameter Explanation Data Type data An integer or long variable to print to datalog long

int i; // create variable 'i' for(i=0; i<10; i++) // cycle through "for loop" ten times (0-9), incrementing 'i' with each iteration: { AddToDatalog(i); // add variable 'i' to the datalog with each iteration of the loop }

bHideDataFiles

word bHideDataFiles

(word) Boolean flag to indicate whether data files should be hidden or shown in the NXT GUI. Note that this is defined as a word but is treated as a bool.

bHideDataFiles = true; // data files will be HIDDEN and NOT SHOW on NXT GUI bHideDataFiles = false; // data files will be SHOWN on NXT GUI

nDatalogSize

word nDatalogSize

(word) The current size allocated to the datalog.

const int size = 2000; // a constant int variable 'size' of size 2000 nDatalogSize = size; // create a new Datalog of size, 'size'

nMaxDataFiles

word nMaxDataFiles

(word) Maximum number of saved datalog files (DATAnnnn.RDT) allowed on a NXT.

nMaxDataFiles = 15; // allow up to 15 Datalog files on one NXT nxtDisplayCenteredTextLine(3, "Max Datalog Files:"); // display on a centered textline on line 3 nxtDisplayCenteredBigTextLine(4, "%d", nMaxDataFiles); // (will display, "15")

nMaxDataFileSize

word nMaxDataFileSize

(word) Maximum size (in 100 byte units) of all datalog files saved on the NXT.

nMaxDataFileSize = 10; // 10*100 = 1000 = roughly 1 kilobyte nxtDisplayCenteredTextLine(3, "Max Datalog Files:"); // display on a centered textline on line 3 nxtDisplayCenteredBigTextLine(4, "%d", nMaxDataFileSize); // (will display, "1000")

nUsedDatalogBytes

const word nUsedDatalogBytes

(word) The number of bytes currently containing data in the datalog.

nMaxDataFileSize = 10; // 10*100 = 1000 = roughly 1 kilobyte while(nMaxDataFileSize - nUsedDatalogBytes > 0) // while there are still bytes left (0 < bytes < size): { AddToDatalog(data); // write to datalog (fill it up!) }

SaveNxtDatalog

void SaveNxtDatalog()

(void) Saves the existing datalog from RAM memory into a NXT file named "DATAnnnn.rdt" where 'nnnn' is numeric and increases by one on every save.

SaveNxtDatalog(); // saves the Datalog