SPI in Real Systems#

SPI is the workhorse bus for high-speed peripheral communication — flash memory, ADCs, displays, and radio transceivers all speak SPI at clock rates from 1 MHz to over 50 MHz. The protocol is simple (clock, data in, data out, chip select), but the four mode/polarity combinations, the chip-select timing requirements, and the DMA integration complexity mean that SPI drivers are where many firmware projects first encounter serious peripheral bugs.

This section covers SPI from the firmware perspective: mode and polarity configuration that matches the device datasheet, chip-select management strategies for single and multi-device buses, DMA-driven transfers that free the CPU for other work, and the bus architecture decisions that determine whether multiple SPI devices can coexist reliably.

Pages#

• SPI Mode Configuration & Clock Polarity — CPOL, CPHA, the four SPI modes, MSB/LSB ordering, and how to read a device datasheet timing diagram to select the correct mode.
• Chip-Select Management — Hardware vs software CS, timing requirements between CS assertion and first clock edge, and multi-device select strategies.
• DMA-Driven SPI Transfers — Configuring DMA for SPI TX/RX, handling the dummy-byte problem, and managing completion callbacks without race conditions.
• Multi-Device SPI Buses — Shared-bus topologies, mixed-speed devices, per-device configuration switching, and when to use separate SPI peripherals instead.