Make prefetch buffer configurable in .ini (#66, #67)

src/ZuluSCSI_disk.cpp

@@ -64,6 +64,9 @@ struct image_config_t: public S2S_TargetCfg
     // Standard SCSI uses left alignment
     // This field uses -1 for default when field is not set in .ini
     int rightAlignStrings;
+
+    // Maximum amount of bytes to prefetch
+    int prefetchbytes;
 };
 
 static image_config_t g_DiskImages[S2S_MAX_TARGETS];
@@ -262,6 +265,7 @@ static void scsiDiskConfigDefaults(int target_idx)
     img.sectorsPerTrack = 63;
     img.headsPerCylinder = 255;
     img.quirks = S2S_CFG_QUIRKS_NONE;
+    img.prefetchbytes = PREFETCH_BUFFER_SIZE;
     memset(img.vendor, 0, sizeof(img.vendor));
     memset(img.prodId, 0, sizeof(img.prodId));
     memset(img.revision, 0, sizeof(img.revision));
@@ -279,6 +283,7 @@ static void scsiDiskLoadConfig(int target_idx, const char *section)
     img.headsPerCylinder = ini_getl(section, "HeadsPerCylinder", img.headsPerCylinder, CONFIGFILE);
     img.quirks = ini_getl(section, "Quirks", img.quirks, CONFIGFILE);
     img.rightAlignStrings = ini_getbool(section, "RightAlignStrings", -1, CONFIGFILE);
+    img.prefetchbytes = ini_getl(section, "PrefetchBytes", img.prefetchbytes, CONFIGFILE);
     
     char tmp[32];
     memset(tmp, 0, sizeof(tmp));
@@ -1101,7 +1106,9 @@ static void diskDataIn()
 
 #ifdef PREFETCH_BUFFER_SIZE
         image_config_t &img = *(image_config_t*)scsiDev.target->cfg;
-        uint32_t prefetch_sectors = PREFETCH_BUFFER_SIZE / bytesPerSector;            
+        int prefetchbytes = img.prefetchbytes;
+        if (prefetchbytes > PREFETCH_BUFFER_SIZE) prefetchbytes = PREFETCH_BUFFER_SIZE;
+        uint32_t prefetch_sectors = prefetchbytes / bytesPerSector;
         uint32_t img_sector_count = img.file.size() / bytesPerSector;
         g_scsi_prefetch.sector = transfer.lba + transfer.blocks;
         g_scsi_prefetch.bytes = 0;

zuluscsi.ini

@@ -24,6 +24,7 @@ MaxSyncSpeed = 10 # Set to 5 or 10 to enable synchronous SCSI mode, 0 to disable
 #SectorsPerTrack = 63
 #HeadsPerCylinder = 255
 #RightAlignStrings = 0 # Right-align SCSI vendor / product strings, defaults on if Quirks = 1
+#PrefetchBytes = 8192 # Maximum number of bytes to prefetch after a read request, 0 to disable
 
 # Settings can be overriden for individual devices.
 [SCSI2]