Motorola IH5 User Manual

5-1

This chapter describes the remote interface provided by the firmware to the 
host CPU via the cPCI bus. This interface facilitates the host obtaining 
information about the board, downloading code and/or data, and execution 
of the downloaded program.

Applications may also be downloaded to the MCPN750A via one 
of the PCI bus windows provided by the PCI-to-PCI bridge. This 
method is faster than using the PPCBug remote interface and may 
be preferable to use for large downloads.

PPCBug uses one of the scratch pad registers of the 2155x PCI-to-PCI 
bridge as the command/response channel. This scratch pad register is 
logically divided into 5 sections:

❏

An ownership flag. When set, indicates that the host ‘owns’ the 
register and is free to write a new command into it. It also indicates 
that the previous command, if any, has been completed and the 
results, if any, have been returned to the register. When the host 
writes a new command to the register, it must clear the ownership 
flag to indicate the register contains a command to be processed.

❏

A ‘command opcode’. This field is a numeric field which specifies 
the command the host desires to be performed.

❏

An error flag which is used to provide command completion status 
to the host CPU.

❏

A ‘command options’ field. This field further qualifies the specifics 
of the command to be performed. The meaning of the option field is 
specific to each command opcode.