cbm_write() added

changed/added some comments
all cbm_* IO functions are using _oserror now


git-svn-id: svn://svn.cc65.org/cc65/trunk@682 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/cbm/cbm_read.c

@@ -12,18 +12,24 @@ int cbm_read(unsigned char lfn, void* buffer, unsigned int size)
 {
     static unsigned int bytesread;
     static unsigned char tmp;
-        
+
+    /* if we can't change to the inputchannel #lfn then return an error */
     if (_oserror = cbm_k_chkin(lfn)) return -1;
     
     bytesread = 0;
-    
+
     while (bytesread<size && !cbm_k_readst()) {
         tmp = cbm_k_basin();
+        
+        /* the kernal routine BASIN sets ST to EOF if the end of file
+         * is reached the first time, then we have store tmp.
+         * every subsequent call returns EOF and READ ERROR in ST, then
+         * we have to exit the loop here immidiatly. */
         if (cbm_k_readst() & 0xBF) break;
+        
         ((unsigned char*)buffer)[bytesread++] = tmp;
     }
     
     cbm_k_clrch();
-    
     return bytesread;
 }