If a soft error occurs, one or more memory bits are corrupted. The memory bits affected can be in the device configuration memory (which determines the behavior of the design), or might be in design memory elements (which determines the state of the design). The following four memory categories represent a majority of the memory in a device:
- Configuration Memory
- Storage elements used to configure the function of the design loaded into the device. This includes function block behavior and function block connectivity. This memory is physically distributed across the entire device and represents the largest number of bits. Only a fraction of the bits are essential to the proper operation of any specific design loaded into the device.
- Block Memory
- High capacity storage elements used to store design state. As the name implies, the bits are clustered into a physical block, with several blocks distributed across the entire device. Block Memory represents the second largest number of bits.
- Distributed Memory
- Medium capacity storage elements used to store design state. This type of memory is present in certain configurable logic blocks (CLBs) and is distributed across the entire device. Distributed Memory represents the third largest number of bits.
- Flip-Flops
- Low capacity storage elements used to store design state. This type of memory is present in all configurable logic blocks (CLBs) and is distributed across the entire device. Flip-Flops represent the fourth largest number of bits.
An extremely small number of additional memory bits exist as internal device control registers and state elements. Soft errors occurring in these areas can result in regional or device-wide interference that is referred to as a single-event functional interrupt (SEFI). Due to the small number of these memory bits, the frequency of SEFI events is considered negligible in this discussion, and these infrequent events are not addressed by the SEM controller.