The naïve solution found in thousands of Arduino tutorials ... How about the MISO line? Most peripherals will disconnect their pins when the chip select signal is active, but there are exceptions.

But we do appreciate the clean and orderly technique that [Eric Rogers] uses to add multiple SPI SRAM chips to an Arduino. The heavy lifting is done with a CPLD shield called the Amani 64.

The Arduino line of open source electronic prototyping ... The AM335x processor also includes two on-chip 200 MHz 32-bit Programmable Real-time Unit (PRU) microcontrollers, which can be used ...