This paper presents a Software Defined Radio (SDR) implementation in C++ of a Multiple Input Multiple Output (MIMO) transceiver platform using the open-source 5G physical layer free5GRAN. The platform evaluates the processing latency of physical layer functions at the receiver on a x86 processor, required for 2 and 4 layer MIMO transmissions. The goal is to verify if the functions can be implemented in software, and integrated into the free5GRAN 5G physical layer. The implemented MIMO transmission schemes are Spatial multiplexing based on V-BLAST and Alamouti Space Frequency Block Coding based on LTE Transmission Mode 2. Results show that MIMO decoding adds significant processing latency that may not respect the time budget for decoding. To reduce latency, functions have been implemented using AVX2 instructions and processing times between sequential and AVX2 execution are compared. Measurements are performed in a Faraday cage and the code will be open-source to provide reproductible results.