Custom Logic

Use the following links to browse through the frequently asked questions relevant to this area of soft design. For more in-depth, visual answers to commonly posed questions, use the links to the corresponding training videos, listed on the right.

Is the Custom Wishbone Interface component's Internal Register item actually a physical register for reading/writing?

When writing a value from the processor to your custom logic, the value will be latched into a register within the Custom Wishbone Interface component. This value persists until the next write to that internal register item.

When the processor is reading a value from your custom logic, the data from the custom logic will be forwarded to the Wishbone DAT_O bus. The data read is not stored in a register within the Custom Wishbone Interface component.

What is the reset value for Internal Register items in a Custom Wishbone Interface component?

After a reset, Internal Register items in the interface will be cleared to zero.

Why can't I use code-level debugging for code added using a C Code Symbol?

Unlike code in an embedded software project, it is not possible to debug C code that is added to an FPGA or Core project through use of a C Code Symbol and C-to-Hardware Compilation technology. This is because the C code in the exported function is transformed into a hardware circuit, not a series of instructions to be carried out by a host processor.

The only available avenue for test is use of a configurable logic analyzer (LAX) virtual instrument.

How do the data types for Parameter-type C Code Entries map to data types used in C source code?

A Parameter-type C Code Entry can be classed as one of the following data types:

• Boolean

• Floating Point

• Unsigned Integer

• Signed Integer.

The Boolean data type corresponds to the bool data type in C, as defined in stdbool.h.

For the Floating Point data type, the associated Precision property can be set to Single or Double. These correspond to 32-bit float and 64-bit double C data types respectively.

For integer data types, the associated Integer Width property can be defined in the range 1 to 64. You are not limited to the widths of C data types. The following table shows the mapping of variable integer widths (defined for the C Code Entry) to C data types.

This mapping becomes especially relevant during synchronization of C Code Entries with corresponding parameters in the exported C function.