We've got some Visual BASIC 4.0 code from an older product that we're thinking about porting to your boards. Does anyone have a sense of how hard this might be? Are there any issues we should know before we decided to go this route?
Visual Basic desktop application code, whether it's version 3, 4, 5 or 6 is not directly portable to eMbedded Visual Basic. While they share the VB name, they have significant differences.
eVB's core is VBScript (a la web design) whereas the VB desktop environments are all VBA (VB for Applications) based, and therefore they are somewhat different. A majority of these differences appeared later in the VB life cycle (most notably versions 5 and 6 with their inclusions of classes and psuedo-inheritance) and therefore VB4 will likely be far more similar to eVB than VB6 would be.
The only way to determine portability is to actually start the port. Application vary so widely that it's nearly impossible without knowing the base code to make any type of estimates for the difficulty of such a port.
A brief list (by all means not everything) that eVB does not have that can make porting difficult:
eVB is interpreted, not compiled
No support for Classes
No support for creating controls
All eVB variables are stored as 16-byte Variants, no matter how you define them in code
No support for command-line parameters
No support for user-defined events
Limited error handling (Only On Error Resume Next)