Attached is the model which i found to be working for DAC-A. The model is created in 2018b version of MATLAB.
I found it working in both interrupt and periodic step time scenario. To get a view of ramp signal I found we need to work with high sample rate else we may not be able to make out the Ramp signal generated. You can either enable periodic/interrupt based approach to test the DAC block. Comment the other implementation which is not used in the model.
The perodic step time is set to 1ms which could give a good ramp signal. The interrupt runs still tight in usec scale. Be sure to tap the correct pin the launchpad for DAC output.
Hope this helps.