ARM System Controller ICST clocks The ICS525 and ICS307 oscillators are produced by Integrated Devices Technology (IDT). ARM integrated these oscillators deeply into their reference designs by adding special control registers that manage such oscillators to their system controllers. The various ARM system controllers contain logic to serialize and initialize an ICST clock request after a write to the 32 bit register at an offset into the system controller. Furthermore, to even be able to alter one of these frequencies, the system controller must first be unlocked by writing a special token to another offset in the system controller. Some ARM hardware contain special versions of the serial interface that only connects the low 8 bits of the VDW (missing one bit), hardwires RDW to different values and sometimes also hardwire the output divider. They therefore have special compatible strings as per this table (the OD value is the value on the pins, not the resulting output divider): Hardware variant: RDW OD VDW Integrator/AP 22 1 Bit 8 0, rest variable integratorap-cm Integrator/AP 46 3 Bit 8 0, rest variable integratorap-sys Integrator/AP 22 or 1 17 or (33 or 25 MHz) integratorap-pci 14 1 14 Integrator/CP 22 variable Bit 8 0, rest variable integratorcp-cm-core Integrator/CP 22 variable Bit 8 0, rest variable integratorcp-cm-mem The ICST oscillator must be provided inside a system controller node. Required properties: - compatible: must be one of "arm,syscon-icst525" "arm,syscon-icst307" "arm,syscon-icst525-integratorap-cm" "arm,syscon-icst525-integratorap-sys" "arm,syscon-icst525-integratorap-pci" "arm,syscon-icst525-integratorcp-cm-core" "arm,syscon-icst525-integratorcp-cm-mem" - lock-offset: the offset address into the system controller where the unlocking register is located - vco-offset: the offset address into the system controller where the ICST control register is located (even 32 bit address) - #clock-cells: must be <0> - clocks: parent clock, since the ICST needs a parent clock to derive its frequency from, this attribute is compulsory. Example: syscon: syscon@10000000 { compatible = "syscon"; reg = <0x10000000 0x1000>; oscclk0: osc0@c { compatible = "arm,syscon-icst307"; #clock-cells = <0>; lock-offset = <0x20>; vco-offset = <0x0c>; clocks = <&xtal24mhz>; }; (...) };