Controlling MCU with FPGA

Hi,

accessing MCU thru FPGA is the unusal way, but may be preferred in some cases where FPGA is owning the primary system interface, e.g. PCIe, ethernet or custom specific interface.

In systems that utilize both FPGA and MCU components, non time-critical communication, configuration and housekeeping jobs are typically assigned to MCU, because they are defined in sequential code and can be implemented there with less resource utilization. But that's a general consideration that must not necessarily apply to your design.

Things depend on which interfaces are already determined by the system topology, what's their bandwidth and which share of interface bandwidth is required for intended communication.

Also interface between MCU and FPGA (no matter which peer is director) will be designed according to bandwidth requirements. In order of increasing throughput we have I2C, UART, SPI, Quad-SPI, parallel data bus (e.g. STM32 FMC interface).

For specifically asked MCU configuration, I agree with @Farabi that serial boot loader is a good method, because it doesn't require previous flash programming, at least in case of STM32. There should be ST code examples for using the boot loader interface in custom code.

Regards
Frank