beneath-apple-dos/D1S2/CH8.3#064000.txt

          Call file manager with CATALOG opcode.
          Set new V value as default for future commands.
          Exit to caller.
.np
A57A-A59D FP command handler.
          Set ROM card, if any, for APPLESOFT (A5B2).
          If successful, coldstart DOS (9D84).
          Otherwise, set status flag to indicate INTEGER BASIC
          is active.
          Set primary filename buffer to "APPLESOFT".
          Set flags to indicate RAM APPLESOFT and coldstart.
          Go to RUN command handler.
.np
A59E-A5B1 INT command handler.
          Set ROM card, if any, for INTEGER BASIC (A5B2).
          If not successful, issue "LANGUAGE NOT AVAILABLE".
          Otherwise, clear RUN intercepted flag.
          Coldstart DOS (9D84).
.np
A5B2-A5C5 Set ROM to desired BASIC.
          (This routine is passed a $4C for APPLESOFT or a $20
          for INTEGER, since these bytes appear at $E000 in
          these BASICs.  It will work regardless of which
          BASIC is onboard)
          If desired BASIC is already available, exit.
          Try selecting ROM card.
          If desired BASIC is now available, exit.
          Try selecting onboard ROM.
          If desired BASIC is now available, exit.
          Otherwise, exit with error return code.
.np
A5C6-A5DC EXEC command handler.
          Open the file (A2A3).
          Copy file buffer address to EXEC's buffer pointer at
          AAB4,AAB5.
          Set EXEC active flag (AAB3).
          Jump into POSITION command handler to skip R lines.
.np
A5DD-A60D POSITION command handler.
          Locate the open file buffer (A764).
          If not found, open one as a TEXT file.
          Copy buffer pointers to file manager parmlist.
          If R was not given on command, exit.
     A5F2 Otherwise, test R value for zero and exit if so.
          Decrement R value by one.
          Read file byte by byte until a carriage return (end
          of line - $8D) is reached.
          If at end of file, issue "END OF FILE" message.
          Otherwise, go to A5F2 to skip next record.
.np
A60E-A625 Write one data byte to file.
          Insure that BASIC is running a program (A65E).
          If not, close file and warmstart DOS.
          Set up file manager parmlist to write the data byte
          to the open file.
          Call file manager and exit.
.np
A626-A65B Read one data byte from file.
          Insure that BASIC is running a program (A65E).
          If not, close file and warmstart DOS.
          Set CSWL intercept state to 6 (skip prompt character)
     A630 Read next file byte (A68C).
          If not at end of file, go to A644.
          Otherwise, close file.
          If state is not 3 (EXEC) issue "END OF DATA" message.
          Exit to caller.
     A644 If data byte is lower case character, turn its most
          significant bit off to fool GETIN routine in monitor.
          Store data byte in A register saved at entry to DOS.
          Using line index, turn high bit back on in previous
          data byte stored at $200 (input line buffer) to make
          it lower case if necessary.
          Exit DOS (9FB3).
.np
A65E-A678 Test to see if BASIC is running a program or is in
          immediate command mode.
          If active BASIC is INTEGER, go to A672.
          If line number is greater than 65280 and prompt is
          "]" then APPLESOFT is in immediate mode.
          Otherwise, it is executing a program.
          Exit to caller with appropriate return code.
     A672 Check $D9 to determine whether BASIC is executing a
          program and exit with proper return code.
.np
A679-A681 Close current file and warmstart DOS.
.np
A682-A68B EXEC read one byte from file.
          Select EXEC file buffer.
          Copy file buffer addresses to file manager parmlist.
          Set state to 3 (input echo).
          Go to A62D to read a file byte.
.np
A68C-A69C Read next text file byte.
          Set up file manager parmlist to read one byte.
          Call file manager driver.
          Return to caller with the data byte.
.np
A69D-A6A7 Set $40,$41 to point to EXEC file buffer.
.np
A6A8-A6C3 File manager driver routine.
          Call the file manager itself (AB06).
          If no errors, exit to caller.
          Otherwise, point $40,$41 at file buffer.
          If found, release it by storing a zero on the file
          name field.
          If error was not "END OF DATA", print error message.
          Otherwise, pretend a $00 was read and return to
          caller.
.np
A6C4-A6D4 Miscellaneous error messages.
     A6C4 "COMMAND SYNTAX ERROR"
     A6C8 "NO FILE BUFFERS AVAILABLE"
     A6CC "PROGRAM TOO LARGE"
     A6D0 "FILE TYPE MISMATCH"
.np
A6D5-A701 Error handler.
          Set warmstart flag and clear status (BFE6).
          If APPLESOFT ONERR is active, go to A6EF.
          Otherwise, print RETURN BELL RETURN.
          Print text of error message (A702).
          Print another RETURN.
     A6EF Replace DOS intercepts.
          If a BASIC program is in execution, pass error code
          to BASIC's error handler.
          Otherwise, warmstart BASIC.
.np
A702-A719 Print text of error message.
          Using the error number as an index, print the message
          text from the message table (A971) byte by byte.
          Last character has most significant bit on.
.np
A71A-A742 Complete file manager parameter list.
          Copy Volume value to parmlist.
          Copy Drive value to parmlist.
          Copy Slot value to parmlist.
          Copy address of primary filename buffer to parmlist.
          Save file buffer address in $40,$41.
          Return to caller.
.np
A743-A74D Copy primary filename to file buffer filename field.
.np
A74E-A75A Copy current buffer pointers to file manager parmlist
          Copy file manager workarea buffer pointer.
          Copy T/S List sector buffer pointer.
          Copy data sector buffer address.
          Copy next file buffer link address.
          Return to caller.
.np
A75B-A763 Reset state to 0 and set warmstart flag.
.np
A764-A791 Locate an open or free file buffer.
          Assume there are no free file buffers by zeroing $45.
          Point $40,$41 at first buffer on chain.
          Go to A773.
     A76E Point $40,$41 at next buffer on chain.
          If at end of chain, exit with file not open code.
     A773 Get first byte of filename field.
          If zero (file buffer free), save file buffer address
          at $44,$45 as an available buffer and go to A76E.
          Otherwise, see if name in primary filename buffer
          matches the name in this file buffer.
          If not, go to A76E to get next buffer.
          If so, return to caller with open file found code.
.np
A792-A799 Point $40,$41 at first file buffer on chain.
.np
A79A-A7A9 Point $40,$41 at next file buffer on chain.
.np
A7AA-A7AE Get first byte of file name in file buffer.
.np
A7AF-A7C3 See if current buffer belongs to EXEC.
          Is EXEC active?
          If not, exit.
          If so, does current buffer address match EXEC's?
          Return to caller with appropriate code.
.np
A7C4-A7D3 Check file type.
          Does file type of open file match desired file type?
          If so, exit.
          Otherwise, turn lock bit off and test again.
          If ok, exit.
          Otherwise, close file and issue "FILE TYPE MISMATCH".
.np
A7D4-A850 Initialize (build) DOS file buffer chain.
          Set $40,$41 to point to first buffer.
          Set counter to MAXFILES value.
     A7E5 Store zero on filename field to mark as free.
          Set up link pointers in buffer to point to file
          manager workarea (45 bytes prior to filename field).
          Set up link pointer to T/S List sector buffer (-256
          bytes from file manager workarea buffer).
          Set up link pointer to data sector buffer 256 bytes
          before that.
          Decrement counter.
          If zero, go to A82D to set HIMEM.
          Otherwise, set link to next file buffer as 38 bytes
          prior to data sector buffer.
          Go to A7E5 to set up next buffer.
     A82D Set link of last buffer to $0000.
          If INTEGER BASIC is active, go to A846.
          Otherwise, set APPLESOFT's HIMEM and STRING START
          pointers in zeropage to point just below the last
          buffer.
          Exit to caller.
     A846 Set INTEGER BASIC's HIMEM and PROGRAM START pointers
          to point just below the last buffer.
          Exit to caller.
.np
A851-A883 Replace DOS keyboard/video intercept vectors.
          Is DOS keyboard (KSWL) vector still set?
          If so, go to A86A.
          Otherwise, save current KSWL vector ($38,$39) at
          AA55,AA56 and replace with DOS intercept routine's
          address.
     A86A Is DOS video (CSWL) vector still set?
          If so, exit to caller.
          Otherwise, save current CSWL vector ($36,$37) at
          AA53,AA54 and replace with DOS intercept routine's
          address.
          Exit to caller.
.nx ch8.4