The DevHlp_RAS function provides a service for device drivers to add information to the System Trace buffer.

Note: DevHlp_RAS is a 16-bit API.

Coding Example.

         MOV   AX,MajorCode           ; major trace event code (240-255)
         MOV   BX,Length              ; length of data area (0-512 bytes)
         MOV   CX,MinorCode           ; minor trace event code (0-255)
         LDS   SI,pData               ; pointer to trace data
         MOV   DL,28H                 ; DevHlp_RAS function code
         CALL  [Device_Help]          ; invoke device helper
16-bit MASM Example

Parameters.

MajorCode

The major code to be placed in the trace buffer. Only the low order byte is used. The high order byte should be 0 for future compatibility reasons, but no error checking of the high order byte is performed.
Length
The length of the area pointed to by the address parameter. If a length greater than 512 is specified, only 512 bytes will be recorded. If a length of 0 is specified, the address parameter will not be used; however, a dummy doubleword must be pushed on the stack so that all calls use the same stack space.
MinorCode
The minor code to be placed in the trace buffer. This code identifies the specific trace event. Only the low order byte is used. The high order byte should be 0 for future compatibility reasons, but no error checking of the high order byte is performed.
pData
The address of the variable length data area which contains additional information that the system trace function will add to the trace buffer. If a length of 0 is specified, the address will not be used, but a value must still be added to the stack.

Results.

         If CF = 0            Trace record placed in trace buffer
         Else
            Data not traced

The possible errors are :

• Tracing suspended
  
• Minor code not being traced
  
• PID not being traced
  
• Trace overrun

Remarks.

The trace facility maintains an array of 32 bytes (256 bits), in which each bit represents a major event code. This array is updated each time the user enables or disables tracing of a major event. The device driver must check this array before calling DevHlp_RAS to ensure that the major event specified is currently enabled for tracing. This array is located in the Global Infoformation Segment.

All registers are preserved. Interrupts are disabled while the trace data is saved and then re-enabled if they were initially enabled.

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