Motorola MCPN750A, IH5 manual

5

Remote Start Via the PCI Bus

❏A command data and result field. This field provides the data, if any, needed by the command and provides the response from PPCBug upon command completion. The meaning of the bits in this field are specific to each command opcode.

Additionally, certain commands require more information than can be contained within the data and result fields of the scratch pad register. To provide this information, the interface provides four ‘virtual’ registers. The contents of these registers are used in certain commands. The contents of the registers can be accessed via commands issued through the scratch register. These registers are designated by the monikers VR0, VR1, VR2 and VR3.

During reset startup, the command/response register is written with a specific reset pattern. This indicates that the local CPU has been reset and is ready to accept commands through the command/response register.

PPCBug uses certain areas of memory and I/O devices for it’s own operation. This interface allows the host CPU to write and read any location on the local CPU bus including those in use by the firmware. Host CPUs should interrogate the firmware via the memory size query command (described in the following paragraph) and avoid overwriting memory which is in-use by firmware - otherwise, erratic behavior may result.

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