Add comments to both Harddisk.cpp & the firmware code about 'sta abs16,x' false-reads, etc.
Harddisk.cpp: Fix typos and update the notes on the r/w commands' operation.
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tomcw
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5ed901f720
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6282790c3d
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@ -49,13 +49,19 @@
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; constants
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hd_execute = $c080
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hd_error = $c081 ; b7=busy, b0=error
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hd_status = $c081 ; b7=busy, b0=error
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hd_command = $c082
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hd_unitnum = $c083
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hd_memblock = $c084
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hd_diskblock = $c086
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;hd_nextbyte = $c088 ; legacy read-only port (still supported by AppleWin)
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; Notes on accesses to I/O registers:
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; . ROR ABS16,X and ROL ABS16,X - only used for $C081+s*$10 STATUS register:
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; 6502: double read (old data), write (old data), write (new data). The writes are harmless as writes are ignored to STATUS.
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; 65C02: double read (old data), write (new data). The write is harmless as writes are ignored to STATUS.
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; . STA ABS16,X does a false-read. This is harmless for writable I/O registers, since the false-read has no side effect.
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command = $42
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unitnum = $43
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memblock = $44
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@ -168,7 +174,7 @@ Bootstrap2
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sta hd_unitnum,x ; b7=0 => disk 1
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sta hd_command,x
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lda hd_execute,x
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ror hd_error,x ; Post: C=0 or 1
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ror hd_status,x ; Post: C=0 or 1
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bcc hdboot
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; no image ready, boot diskette image instead
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@ -272,7 +278,7 @@ GetSlotInX
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; C=1 => via GetSlotInX (eg. Entrypoint / SmartPort2)
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; X = Slot# << 4
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; Post:
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; C = hd_error.b0
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; C = hd_status.b0
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; A = result of hd_execute
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; X = Slot# << 4
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cmdproc
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@ -292,17 +298,17 @@ cmdproc
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sta hd_diskblock+1,x
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lda hd_execute,x ; A = result of hd_execute (NB. instantaneous 512 byte r/w!)
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- rol hd_error,x ; b7=busy doing DMA?
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- rol hd_status,x ; b7=busy doing DMA?
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bcs -
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plp ; restore C from start of cmdproc
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bcs done
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ror hd_error,x ; Post: C=0 or 1
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ror hd_status,x ; Post: C=0 or 1
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lda #0
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beq hdboot2
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done
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ror hd_error,x ; Post: C=0 or 1
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ror hd_status,x ; Post: C=0 or 1
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rts
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;======================================
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@ -42,54 +42,64 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#include "../resource/resource.h"
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/*
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Memory map:
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Memory map (for slot 7):
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C0F0 (r) EXECUTE AND RETURN STATUS
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C0F1 (r) STATUS (or ERROR)
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C0F1 (r) STATUS (or ERROR): b7=busy, b0=error
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C0F2 (r/w) COMMAND
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C0F3 (r/w) UNIT NUMBER
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C0F4 (r/w) LOW BYTE OF MEMORY BUFFER
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C0F5 (r/w) HIGH BYTE OF MEMORY BUFFER
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C0F6 (r/w) LOW BYTE OF BLOCK NUMBER
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C0F7 (r/w) HIGH BYTE OF BLOCK NUMBER
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C0F8 (r) NEXT BYTE
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C0F8 (r) NEXT BYTE (legacy read-only port - still supported)
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Firmware notes:
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. ROR ABS16,X and ROL ABS16,X - only used for $C081+s*$10 STATUS register:
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6502: double read (old data), write (old data), write (new data). The writes are harmless as writes to STATUS are ignored.
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65C02: double read (old data), write (new data). The write is harmless as writes to STATUS are ignored.
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. STA ABS16,X does a false-read. This is harmless for writable I/O registers, since the false-read has no side effect.
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*/
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/*
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Hard drive emulation in Applewin.
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Hard drive emulation in AppleWin.
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Concept
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To emulate a 32mb hard drive connected to an Apple IIe via Applewin.
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To emulate a 32mb hard drive connected to an Apple IIe via AppleWin.
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Designed to work with Autoboot Rom and Prodos.
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Overview
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1. Hard drive image file
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The hard drive image file (.HDV) will be formatted into blocks of 512
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bytes, in a linear fashion. The internal formatting and meaning of each
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block to be decided by the Apple's operating system (ProDos). To create
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an empty .HDV file, just create a 0 byte file (I prefer the debug method).
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block to be decided by the Apple's operating system (ProDOS). To create
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an empty .HDV file, just create a 0 byte file.
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2. Emulation code
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There are 4 commands Prodos will send to a block device.
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There are 4 commands ProDOS will send to a block device.
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Listed below are each command and how it's handled:
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1. STATUS
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In the emulation's case, returns only a DEVICE OK (0) or DEVICE I/O ERROR (8).
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DEVICE I/O ERROR only returned if no HDV file is selected.
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In the emulation's case, returns only a DEVICE OK (0), DEVICE I/O ERROR ($27) or DEVICE NOT CONNECTED ($28)
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DEVICE NOT CONNECTED only returned if no HDV file is selected.
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2. READ
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Loads requested block into a 512 byte buffer by attempting to seek to
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location in HDV file.
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If seek fails, returns a DEVICE I/O ERROR. Resets hd_buf_ptr used by HD_NEXTBYTE
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If seek fails, returns a DEVICE I/O ERROR. Resets m_buf_ptr used by legacy HD_NEXTBYTE
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Copies requested block from a 512 byte buffer to the Apple's memory.
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Sets STATUS.busy=1 until the DMA operation completes.
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Returns a DEVICE OK if read was successful, or a DEVICE I/O ERROR otherwise.
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3. WRITE
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Copies requested block from the Apple's memory to a 512 byte buffer
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then attempts to seek to requested block.
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If the seek fails (usually because the seek is beyond the EOF for the
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HDV file), the Emulation will attempt to "grow" the HDV file to accomodate.
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Once the file can accomodate, or if the seek did not fail, the buffer is
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HDV file), the emulation will attempt to "grow" the HDV file to accommodate.
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Once the file can accommodate, or if the seek did not fail, the buffer is
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written to the HDV file. NOTE: A2PC will grow *AND* shrink the HDV file.
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Sets STATUS.busy=1 until the DMA operation completes.
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I didn't see the point in shrinking the file as this behaviour would require
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patching prodos (to detect DELETE FILE calls).
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@ -99,9 +109,9 @@ Overview
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3. Bugs
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The only thing I've noticed is that Copy II+ 7.1 seems to crash or stall
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occasionally when trying to calculate how many free block are available
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occasionally when trying to calculate how many free blocks are available
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when running a catalog. This might be due to the great number of blocks
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available. Also, DDD pro will not optimise the disk correctally (it's
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available. Also, DDD pro will not optimise the disk correctly (it's
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doing a disk defragment of some sort, and when it requests a block outside
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the range of the image file, it starts getting I/O errors), so don't
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bother. Any program that preforms a read before write to an "unwritten"
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