Motorola MVME166IG/D2, MVME166D2 manual 166Bug Vector Table and Workspace, Hardware Functions

Using the 166Bug Debugger

If your application enables translation through the Memory Management Units (MMUs), and if your application utilizes resources of the debugger (e.g., system calls), your application must create the necessary translation tables for the debugger to have access to its various resources. The debugger honors the enabling of the MMUs; it does not disable translation.

166Bug Vector Table and Workspace

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As described in the Memory Requirements section in Chapter 3, 166Bug needs 64KB of read/write memory to operate. The 166Bug reserves a 1024-byte area for a user program vector table area and then allocates another 1024-byte area and builds an exception vector table for the debugger itself to use. Next, 166Bug reserves space for static variables and initializes these static variables to predefined default values. After the static variables, 166Bug allocates space for the system stack, then initializes the system stack pointer to the top of this area.

With the exception of the first 1024-byte vector table area, you must be extremely careful not to use the above-mentioned memory areas for other purposes. You should refer to the Memory Requirements section in Chapter 3 to determine how to dictate the location of the reserved memory areas. If, for example, your program inadvertently wrote over the static variable area containing the serial communication parameters, these parameters would be lost, resulting in a loss of communication with the system console terminal. If your program corrupts the system stack, then an incorrect value may be loaded into the processor Program Counter (PC), causing a system crash.

Hardware Functions

The only hardware resources used by the debugger are the EIA-232-D ports, which are initialized to interface to the debug terminal. If these ports are reprogrammed, the terminal characteristics must be modified to suit, or the ports should be restored to the debugger-set characteristics prior to reinvoking the debugger.

4-10 MVME166 Single Board Computer Installation Guide