MAG-IOL, I$MA

* ????-???-???? (MAG-IOL) DRAWING NO. 41285823-001-01 PAGE 5

0201 * MODIFIED TO INCLUDE THE APPROPRIATE MTU NUMBER BY CALLING M$SETU, 0202 * PASSING A ZERO-TERMINATED TABLE OF ADDRESSES OF THE I/O 0203 * INSTRUCTIONS TO BE MODIFIED. M$SETU IS PASSED THE LOGICAL UNIT 0204 * NUMBER AND CALLS M$UNIT TO MAP THIS TO THE APPROPRIATE PHYSICAL 0205 * UNIT NUMBER. 0206 * 0207 * I$MAGT IS NOT INTENDED TO BE CALLED DIRECTLY, INSTEAD RECORDS ARE 0208 * READ BY CALLING ONE OF I$MA, I$MB, OR I$MC. THE RETURN ADDRESS OF 0209 * THE CALL TO THIS (I$MX) ROUTINE IS PASSED TO I$MAGT IN THE INDEX 0210 * REGISTER, ALLOWING THE BUFFER ADDRESS, BUFFER SIZE, AND LOGICAL 0211 * UNIT NUMBER PARAMETERS TO BE LOCATED, AND THE APPROPRIATE RETURN 0212 * ADDRESS TO BE COMPUTED. THE CALL TO I$MAGT (FROM I$MX) IS FOLLOWED 0213 * BY AN OCP INSTRUCTION THAT INDICATES THE TYPE OF RECORD TO BE 0214 * READ. I$MAGT DOES NOT RETURN TO ITS (I$MX) CALLER BUT INSTEAD 0215 * RETURNS DIRECTLY TO THE APPOPRIATE RETURN LOCATION IN THE I$MX 0216 * CALL SEQUENCE. 0217 * 0218 * SIMILARLY, RECORDS ARE WRITTEN BY CALLING ONE OF O$MA, O$MB, OR 0219 * O$MC WHICH IN TURN CALLS O$MAGT. 0220 * 0221 * CONTROL OPERATIONS (C$FR, C$FF, C$BR, C$BF, AND C$MR) CALL 0222 * C$MAGT, WITH THE CALL TO C$MAGT BEING FOLLOWED BY THE OCP 0223 * INDICATING THE REQUIRED CONTROL OPERATION. IN THE CASE OF 0224 * SPACING BY A RECORD A RETURN LOCATION IS USED THAT INDICATES 0225 * END-OF-FILE BEING REACED. THOSE OPERATIONS THAT ALWAYS MOVE 0226 * TO THE START OR END OF A FILE (C$FF, C$BF, AND C$MR) DO NOT 0227 * HAVE THE EOF RETURN LOCATION. 0228 * 0229 * EACH OF THE GENERAL ROUTINES (I$MAGT, O$MAGT, AND C$MAGT) CALL 0230 * M$NBRW TO ENSURE THAT THE MTU IS NOT BUSY AND THE TAPE IS NOT 0231 * WINDING. THE ADDRESSES OF TWO SKS INSTRUCTIONS IN THAT ROUTINE 0232 * NEED TO BE INCLUDED IN THE TABLE OF I/O ISNTRUCTION ADDRESSES 0233 * PASSED TO M$SETU. M$NBR1 AND M$NBR2 ARE SYMBOLS PROVIDED FOR 0234 * THIS PURPOSE. 0235 * 0236 * A DEFAULT M$UNIT IS INCLUDED IN THE LIBRARY THAT USES THE 0237 * LOGICAL UNIT NUMBER DIRECTLY AS THE PHYSICAL NUMBER. IT MAY 0238 * BE REPLACED BY A ROUTINE THAT DOES ACTUALLY MAP UNIT NUMBERS. 0239 * THIS ROUTINE MAY MODIFY THE INDEX REGISTER. 0240 * 0241 EJCT