Visible to Intel only — GUID: iga1405558422226
Ixiasoft
Visible to Intel only — GUID: iga1405558422226
Ixiasoft
5.4.3.5. slaveselect Register
The slaveselect register is a bit mask for the ss_n signals driven by an SPI host. During a serial shift operation, the SPI host selects only the agent device(s) specified in the slaveselect register.
The slaveselect register is only present when the SPI core is configured in host mode. There is one bit in slaveselect for each ss_n output, as specified by the designer at system generation time. The slaveselect register value is only updated either at the beginning of the actual SPI transmission or when the SSO bit is set from 0 to 1.
A host peripheral can set multiple bits of slaveselect simultaneously, causing the SPI host to simultaneously select multiple agent devices as it performs a transaction. For example, to enable communication with agent devices 1, 5, and 6, set bits 1, 5, and 6 of slaveselect. However, consideration is necessary to avoid signal contention between multiple agents on their miso outputs.
Upon reset, bit 0 is set to 1, and all other bits are cleared to 0. Thus, after a device reset, agent device 0 is automatically selected.