System information

5.1 USB Device Emulation

After the daemon detects an active interrupt, it acknowledges the request. Figure 5.6

illustrates the process of this protocol.

AHB-HPI

Bridge

Interrupt Port

MSBO

Daemon

MSBO

Firmware

AHB

Acknowledge Port

...

Command Port

Data Pointer Port

Size Port

...

SRAM

2. polling

5. read out

ARM CPU

USB Controller

3. set

6. reset

1. set

4. reset

Figure 5.6: Processing of an MSBO message. The numbers represent the time ﬂow of the

processing steps.

To avoid raise conditions, the MESSAGE_ACK_PORT is written only by the daemon

and read out by the ﬁrmware. In opposite, the MESSAGE_INTERRUPT_PORT is written

by the ﬁrmware and read out by the daemon. The ﬁrmware resets the interrupt after the

detection of the acknowledgment. This is the same handshaking mechanism used for the

VGA processing entities (shown in section 4.2.2). At the time, the daemon reads out the

message. Afterwards, the daemon resets the acknowledgment.

SCSI Command Processing

The ﬁrmware generates a MESSAGE_CMD_SCSI_CMD message, when a SCSI command

from the host arrived. Afterwards the daemon processes the SCSI command. The daemon

does not acknowledge the MESSAGE_CMD_SCSI_CMD until the SCSI command is pro-

cessed. Following steps are passed through while SCSI command processing:

• Host send an SCSI command to the CHARM.

• MSBO ﬁrmware sends a MESSAGE_CMD_SCSI_CMD message.

• MSBO daemon process the SCSI command.

• MSBO daemon acknowledges the MESSAGE_CMD_SCSI_CMD message.

• MSBO ﬁrmware sends a response to the host.