/**********************************************************
*							  *
*	process_cmd(): This routine fetches the first     *
*		       command byte and executes the 	  *
*		       instruction.			  *
*							  *
**********************************************************/

process_cmd()
{
	int i;
	switch(com[0])
	{
		case TEST_UNIT_READY: ck_printer();
				      break;

		case REQUEST_SENSE: send_sense();
				    break;

		case PRINT:	if (sense[0])				/* Printer possibly in error state	*/
				{
					stat=CHECK_CONDITION;		/* Initiator must check sense before continuing	*/
					break;
				}
				data_len = (com[4] + (com[3] * 256));			/* Read the amount of data to be sent	*/
				if (!reserved || com[2] || !data_len || (data_len > BUFFLIM))
										/* Check the amount of data is not greater  	*/
				{						/* than the buffer limit, or equal to zero   	*/
					sense[0]=ILLEGAL_REQUEST;
					stat=CHECK_CONDITION;
				}
				else
					print_cmd();		/* DMA into buffer data_len of data	*/
			    	break;

		case RESERVE_UNIT: if (!initid)
				   {
					sense[0]=ILLEGAL_REQUEST;
					stat=CHECK_CONDITION;
				   }
				   else
				   {
				   	if (reserved && (reserved != initid))
						stat=RESERVATION_CONFLICT;
				   	else
						reserved=initid;
				   }
				   break;

		case RELEASE_UNIT:  if (!reserved)
				    {
					sense[0]=ILLEGAL_REQUEST;
					stat=CHECK_CONDITION;
				    }
				    else
				    {
					if (reserved && (reserved != initid))
						stat=RESERVATION_CONFLICT;
				   	else
						reserved=FALSE;
				    }
				    break;

		case FLUSH_BUFFER:  write(PIOC, (LED_ON | PRINTER_INIT));	/* Re-initialise printer to empty any buffer	*/
				    write(PIOC,LED_ON);
				    print_on = in_print = FALSE;	/* Stop print	*/
				    front = rear = bottom;		/* Empty SPC buffer	*/
				    break;

		case FORMAT:
		case SLEW_PRINT:
		case INQUIRY:
		case RECOVER_BUFFERED_DATA:
		case MODE_SELECT:
		case COPY:
		case MODE_SENSE:
		case STOP_PRINT:
		case RECEIVE_DIAGNOSTIC_RESULTS:
		case SEND_DIAGNOSTICS:
		default: sense[0]=ILLEGAL_REQUEST;
			 stat=CHECK_CONDITION;
	}
}

/**********************************************************
*							  *
*	ck_printer(): This is called in response to a     *
*		      'test unit ready' command.It checks *
*		      the printer and updates the status  *
*		      buffer and the sense data.	  *
*							  *
**********************************************************/

ck_printer()
{
	if(read(PIOB) & PRINTER_ERROR)
	{
		if(!(read(PIOB) & PRINTER_PE))
		{
			sense[0]=MEDIUM_ERROR;
			stat=CHECK_CONDITION;
		}
		else
		{
			sense[0]=UNIT_ATTENTION;
			stat=CHECK_CONDITION;
		}
	}
	else
	{
		sense[0]=NO_SENSE;
		stat=GOOD;
	}
}

/**********************************************************
*							  *
*	send_sense(): In response to a 'request sense'    *
*		      command this routine sends the data *
*		      contained in the status buffer,     *
*		      using a DMA transfer.		  *
*							  *
**********************************************************/

send_sense()
{
	if(com[4] > MAX_SENSE)				/* This byte indicates that the initiator requests extended 	*/
	{						/* sense which this software does not support.			*/
		sense[0]=ILLEGAL_REQUEST;
		stat=CHECK_CONDITION;
	}
	else
	{
		write(DMAMCL,DONT_CARE);
		write(DMAMOD,(SINGLE_MODE | READ_TRANSFER));
		write(DMAMSK,CHANNEL0);
		dmawrit(DMAADD,&sense[0]);
		dmawrit(DMACNT,(SENSE_BYTES-1));
		single_dma_in(DATA_IN);
	}
}