System information

4 Graphic Card Implementation

4.3.2 Host Interface of the RPC

The CHARM provides three 32-bit I/O ports for the RPC communication: command, data

and status port. The host computer can send or receive RPC commands with the aid of

these I/O ports. The I/O ports are deﬁned by the PCI Base Address Register of the PCI

core.

RPC Command Port receives or provides RPC command IDs. An RPC command is a

task or an information for the receiver of the command. The command ID deﬁnes a

speciﬁc RPC command. The ID is written to the command port and setups a new

RPC command for the CHARM. Afterwards, the RPC data port is ready to accept

data. Writing to the command port again, executes the RPC command. Thereby, the

host can either start a new RPC command or reset the command port. The command

port can be reset by writing the RPC Reset command to the command port. Table

4.5 shows a list of all RPC commands.

RPC Data Port receives or provides data which relates to the RPC command. The RPC

data is part of the command and can specify a sub-command or data which has to

be processed by the receiver. Some RPC commands do not have a data ﬁeld and the

data port is not used in this case.

RPC Status Port provides the state of the input or output FIFO of the RPC data port.

Data cannot be written if the status port returns a full input FIFO.

The diagram 4.16 illustrates the ﬂow of sending an RPC command. First, the host writes

the RPC command ID to the RPC command port. Before the host can send data to the

CHARM, it has to check the state of the input FIFO. The input FIFO synchronizes the

data ﬂow of the host to the CHARM. It is implemented in software and is part of the RPC

kernel driver (section 4.3.3 explains the RPC driver). After the transfer of the RPC data,

the host writes again to the RPC command port to signal the end of the RPC message.

Receiving an RPC command is quite similar to the sending of an RPC command. The

UML diagram 4.17 illustrates this process. The host reads out periodically the RPC com-

mand port until it receives an RPC command ID which is diﬀerent to the ID of the RPC

Reset command. The RPC status port provides information whether the RPC command

contains additional data. After reading the RPC message, the host executes the command.

Afterwards, the host can read out the command and data port again until all pending RPC

commands are executed.

ID Command Description

0 RPC_COMMAND_RESET Marks the end of a command.

1 RPC_TEXT_MESSAGE Sends a text message.

2 RPC_CMOS_DATA Contains the CMOS content of the host.

3 RPC_DMI_DATA Contains the DMI content of the host.

Table 4.5: RPC Commands.