Command Code:

cmdDBG_STEP = 13

Host-to-Stem Packet:

0		1		2		3		4		5
address		4		cmdDBG_STEP		ProcID		Opcode		OpData

ProcID -	Index of a VM process.  Range is 0-3.
Opcode -	VM instruction opcode.
OpData -	0-2 bytes of data for VM instruction.

Reply Packet:

0		1		2		3		4		5		6		7		8		9
address		8		cmdDBG_STEP		ProcID		DBGSTAT		PCH		PCL		SPH		SPL		FLAGS

ProcID -	Index of a VM process.  Range is 0-3.
DBGSTAT -	Status of debugging process.
PCH -	High byte of 16-bit program counter.
PCL -	Low byte of 16-bit program counter.
SPH -	High byte of 16-bit stack pointer.
SPL -	Low byte of 16-bit stack pointer.
FLAGS -	Contents of flag register.

Description:

This command executes a single instruction in an active debugging process.  A process ID that is out of range will generate an error message.  A process ID for an inactive process or an active process that is not in debug mode will generate an error message.

The reply packet is tagged with the cmdDBG_STEP code.  It contains the process ID, debug status, program counter, stack pointer, and flag register.

The DBGSTAT is 0 if the operation completes normally.  It is 1 if the process exits after an error or normal execution of an exit opcode.  The bits in the FLAGS byte are described below.