Make aligned reads from the SD card for the D8 cmd

The code  now fetches data from the SD card aligned on 512 byte
boundaries. This means prefetching and post-fetching from the SD card
so the unaligned 2352 byte CD sector size can properly fit in the
buffer. To be written over the SCSI bus.

The end case where the last CD sector is read hasn't been addressed yet,
so in theory the buffering code could attempt to read past the end
of the SD card.

src/ZuluSCSI_cdrom.cpp

@@ -33,6 +33,7 @@
 #include "ZuluSCSI_config.h"
 #include <CUEParser.h>
 #include <assert.h>
+#include <minIni.h>
 #ifdef ENABLE_AUDIO_OUTPUT
 #include "ZuluSCSI_audio.h"
 #endif
@@ -1838,6 +1839,73 @@ static bool doReadCapacity(uint32_t lba, uint8_t pmi)
     return true;
 }
 
+static void doReadD8(uint32_t lba, uint32_t length, int sector_length, int read_size)
+{
+    image_config_t &img = *(image_config_t*)scsiDev.target->cfg;
+    uint8_t *buf0 = scsiDev.data;
+    uint8_t *buf1;// = scsiDev.data + read_length;
+    // Adjust for plextor d8 offset
+    if (lba - 2 < 0)
+    {
+        logmsg("Error - lba is negative after plextor d8 2 sector adjustment");
+    }
+    lba = lba -2;
+
+    uint64_t offset = lba * sector_length;
+
+
+    scsiDev.phase = DATA_IN;
+    scsiDev.dataLen = 0;
+    scsiDev.dataPtr = 0;
+    scsiEnterPhase(DATA_IN);
+    // Format the sectors for transfer
+    for (uint32_t idx = 0; idx < length; idx++)
+    {
+        platform_poll();
+        diskEjectButtonUpdate(false);
+
+        // Where in bytes the sector starts in the image file
+        uint64_t sector_start = offset + idx * sector_length;
+        // Where to start reading the image file in bytes, aligned at or before sector start
+        uint64_t aligned_start = (sector_start / read_size) * read_size; 
+        // The difference between the sector start and aligned start
+        uint32_t sector_start_offset = (uint32_t)(sector_start - aligned_start);
+        // Where the sector on the CD ends in bytes
+        uint64_t sector_end = sector_start + sector_length - 1;
+        // The number of aligned blocks on the image file to read rounded up
+        uint32_t number_of_read_sectors = (sector_end - aligned_start + read_size - 1) / read_size;
+        // How many bytes to read from the image file
+        uint32_t aligned_read_length = number_of_read_sectors * read_size;
+        img.file.seek(aligned_start);
+
+        // Verify that previous write using this buffer has finished
+        uint8_t *buf = ((idx & 1) ? buf1 : buf0);
+        uint8_t *bufstart = buf + sector_start_offset;
+        uint32_t start = millis();
+        while (!scsiIsWriteFinished(bufstart + sector_length - 1) && !scsiDev.resetFlag)
+        {
+            if ((uint32_t)(millis() - start) > 5000)
+            {
+                logmsg("doReadD8() timeout waiting for previous to finish");
+                scsiDev.resetFlag = 1;
+            }
+            platform_poll();
+            diskEjectButtonUpdate(false);
+        }
+        if (scsiDev.resetFlag) break;
+
+        // User data
+        img.file.read(buf, aligned_read_length);
+
+        scsiStartWrite(bufstart, sector_length);
+    }
+
+    scsiFinishWrite();
+
+    scsiDev.status = 0;
+    scsiDev.phase = STATUS;
+}
+
 /**************************************/
 /* CD-ROM command dispatching         */
 /**************************************/
@@ -2146,6 +2214,10 @@ extern "C" int scsiCDRomCommand()
         const uint32_t CD_C2_SIZE = 294;
         const uint32_t CD_SUBCODE_SIZE = 96;
         const uint32_t CD_RAW_DATA_SIZE = CD_DATA_SIZE + CD_C2_SIZE + CD_SUBCODE_SIZE;
+        uint32_t bytes_per_sector = 0;
+        bytes_per_sector = ini_getl("SCSI","PlextorBytesPerSector", 0, CONFIGFILE);
+        uint32_t bytes_per_block = ini_getl("SCSI", "PlextorBytesPerBlock", 512 , CONFIGFILE);
+        if (bytes_per_sector == 0) bytes_per_sector = CD_DATA_SIZE;
         uint8_t lun = scsiDev.cdb[1] & 0x7;
         uint8_t subcode = scsiDev.cdb[10];
         if (lun != 0)
@@ -2170,11 +2242,8 @@ extern "C" int scsiCDRomCommand()
                 (((uint32_t) scsiDev.cdb[7]) << 16) +
                 (((uint32_t) scsiDev.cdb[8]) << 8) +
                 scsiDev.cdb[9];
-            uint32_t original_bytes_per_sector = scsiDev.target->liveCfg.bytesPerSector;
-            scsiDev.target->liveCfg.bytesPerSector = CD_RAW_DATA_SIZE; 
-            dbgmsg("Doing a Plextor 0xD8 CDDA Read, starting: ", (int)lba, " length: ",(int)blocks, " byte-per-sector:", (int) CD_RAW_DATA_SIZE );
-            scsiDiskStartRead(lba, blocks);
-            scsiDev.target->liveCfg.bytesPerSector = original_bytes_per_sector;
+            dbgmsg("Doing a Plextor 0xD8 CDDA Read, starting: ", (int)lba, " length: ",(int)blocks, " byte-per-sector: ", (int) bytes_per_sector, " byte=per=block: ", (int) bytes_per_block );
+            doReadD8(lba, blocks, bytes_per_sector, bytes_per_block);
         }
     }
     else if (command == 0x4E)