From: Chris Bostic <cbostic@xxxxxxxxxx> Add details on the basic functions of the FSI serial bus. Signed-off-by: Chris Bostic <cbostic@xxxxxxxxxx> --- Documentation/devicetree/bindings/fsi/fsi.txt | 54 +++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) create mode 100644 Documentation/devicetree/bindings/fsi/fsi.txt diff --git a/Documentation/devicetree/bindings/fsi/fsi.txt b/Documentation/devicetree/bindings/fsi/fsi.txt new file mode 100644 index 0000000..7fa2394 --- /dev/null +++ b/Documentation/devicetree/bindings/fsi/fsi.txt @@ -0,0 +1,54 @@ +FSI: Flexible Support processor Interface + +FSI is a two line serial bus capable of running at speeds up to 166 MHz. +The lines consist of a clock responsible for synchronizing the target device +(slave) with the master which is responsible for all transactions on the bus. +The master owns the clock line and is the only side allowed to change its +state. The second line, SDA, is a data line that conveys information to/from +the slave who samples based on the clock line. The data line is +bi-directional. + +The master initiates communication by sending a command to the slave and +depending on the type of command will allow the slave to control the bus +to return requested data. All commands are CRC protected. The slave upon +receipt of a command will determine if the CRC is correct and discard +the data if noise has corrupted the line. In the same manner the master +will verify the CRC received from the slave. + +Types of commands: +Read 32 bit: Read a 32 bit word from a specified address on the slave. +Read 16 bit: Read a 16 bit 'half word' from a specified address on the slave. +read 8 bit: Read a byte from a specified address on the slave. +Write 32,16,8 bit: Write to a specified address on the slave with the provided + data. +BREAK: Initialize the slave's logic to receive commands. +TERM: Terminate the slave's error lockout to resume communications + after an error on the bus is detected. +D-POLL: Poll the slave to determine when it is no longer buy processing + a previous command. +I-POLL: Interrupt signal check. Master queries slave to see if any + interrupts are asserting. + +High fanout capability: +FSI buses can be chained together in 'hub' configurations to expand the +available communications channels and thus allow connetion to more slaves. + + +Typical implementation + + FSI master ----- slave with local FSI master (hub) ------- downstream slave + + +Each two line combination of a clock and data line is collectively referred +to as a 'FSI link'. Depending on hardware the primary FSI master may support +up to 64 links. Hub FSI masters can support at most 8 links. Total number +of supported slaves can grow exponentially depending on how many hubs are +placed in the path. Presently only two hubs in the chain are allowed but +in the future this may be expanded. + +The slave hardware logic responsible for decoding FSI master commands is +contained in a CFAM (Common Field replaceable unit Access Macro). Up to +4 slaves or CFAMs can be connected on each FSI link. CFAMs in addition +to the slave logic (or engine) can contain other functions that allow access +via FSI. Common additional functionality includes I2C masters, GPIO +controllers, UARTs, etc... -- 1.8.2.2 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
