SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
If multiple slave devices exist, the master generates a separate slave select
signal for each slave. These relationships are illustrated in Figure 32.
The master generates slave select signals using general-purpose discrete
input/output pins or other logic. This consists of old-fashioned bit banging
and can be pretty sensitive. You have to time it relative to the other signals
and ensure, for example, that you don't toggle a select line in the middle of a
frame.
Figure 32: SPI with Multi-Slave Configuration
