SPI

The Duckbill SPI is intended to be used in the evaluation kit “PLC bundle for Internet of Things”. Thus the device tree file contains a section which refers to the Qualcomm Atheros QCA7000 serial-to-powerline bridge.

The settings for the QCA driver are listed in the following table.

Attribute	Source	SSP2
Type	Modprobe config	External
MAC address	Device tree	Value from OTP
Max SPI clock rate	Device tree	8 MHz
Actual SPI clock rate	Clock tree	6 MHz
SPI mode	Device tree	3
Expected SPI slave	Device tree	QCA7000
Expected command mode	Device tree	burst

The device tree binding for the QCA driver can be found in the Kernel sources: Documentation/devicetree/bindings/net/qca-qca7000-spi.txt

Note 1: The MAC address is added dynamically by U-Boot into the device tree.

Note 2: The reference clock for SSP2 is switched from ref_io1 to ref_xtal by an additional kernel patch. This limits the maximum SPI frequency to 12 MHz. This is due to observed bit errors when ref_io1 is used as clock source. However, for the use-case with QCA7000, the maximum clock rate is already limited by the QCA7000 which only supports up to 12 MHz. The reason for the actual 6 MHz is, that the SPI leaves the Duckbill via the connector and “flying wires”.

Due the limitation of the selected clock and SPI the following SPI clock rates are available:

• 12.0 MHz
• 6.0 MHz
• 4.0 MHz
• 3.0 MHz
• 2.4 MHz
• 2.0 MHz
• 1.72 MHz
• 1.5 MHz
• 1.34 MHz
• 1.2 MHz
• 1.1 MHz
• 1.0 MHz