Reduced SPIFFS cache, freeing ~0.5k RAM.

Also made the cache on/off configurable via user_config.h. Uncached writes
are not a very good idea, but for read-only deployments a further ~0.5k RAM
can be gained by disabling the cache.

Tweaked the file.read() workhorse to read large chunks at a time rather
than use getc(), to compensate for potential unavailability of cache.

app/include/user_config.h

@@ -47,6 +47,8 @@
 // #define BUILD_WOFS		1
 #define BUILD_SPIFFS	1
 
+#define SPIFFS_CACHE 1
+
 // #define LUA_NUMBER_INTEGRAL
 
 #define LUA_OPTRAM

app/modules/file.c

@@ -196,11 +196,10 @@ static int file_fsinfo( lua_State* L )
 // g_read()
 static int file_g_read( lua_State* L, int n, int16_t end_char )
 {
-  if(n< 0 || n>LUAL_BUFFERSIZE) 
+  if(n <= 0 || n > LUAL_BUFFERSIZE)
     n = LUAL_BUFFERSIZE;
   if(end_char < 0 || end_char >255)
     end_char = EOF;
-  int ec = (int)end_char;
   
   luaL_Buffer b;
   if((FS_OPEN_OK - 1)==file_fd)
@@ -208,27 +207,22 @@ static int file_g_read( lua_State* L, int n, int16_t end_char )
 
   luaL_buffinit(L, &b);
   char *p = luaL_prepbuffer(&b);
-  int c = EOF;
+  int i;
-  int i = 0;
 
-  do{
+  n = fs_read(file_fd, p, n);
-    c = fs_getc(file_fd);
+  for (i = 0; i < n; ++i)
-    if(c==EOF){
+    if (p[i] == end_char)
+    {
+      ++i;
       break;
     }
-    p[i++] = (char)(0xFF & c);
-  }while((c!=EOF) && (c!=ec) && (i<n) );
-
-#if 0
-  if(i>0 && p[i-1] == '\n')
-    i--;    /* do not include `eol' */
-#endif
 
   if(i==0){
     luaL_pushresult(&b);  /* close buffer */
     return (lua_objlen(L, -1) > 0);  /* check whether read something */
   }
 
+  fs_seek(file_fd, -(n - i), SEEK_CUR);
   luaL_addsize(&b, i);
   luaL_pushresult(&b);  /* close buffer */
   return 1;  /* read at least an `eol' */ 

app/spiffs/spiffs.c

@@ -8,7 +8,9 @@ spiffs fs;
   
 static u8_t spiffs_work_buf[LOG_PAGE_SIZE*2];
 static u8_t spiffs_fds[32*4];
-static u8_t spiffs_cache[(LOG_PAGE_SIZE+32)*4];
+#if SPIFFS_CACHE
+static u8_t spiffs_cache[(LOG_PAGE_SIZE+32)*2];
+#endif
 
 static s32_t my_spiffs_read(u32_t addr, u32_t size, u8_t *dst) {
   platform_flash_read(dst, addr, size);
@@ -62,8 +64,12 @@ void myspiffs_mount() {
     spiffs_work_buf,
     spiffs_fds,
     sizeof(spiffs_fds),
+#if SPIFFS_CACHE
     spiffs_cache,
     sizeof(spiffs_cache),
+#else
+    0, 0,
+#endif
     // myspiffs_check_callback);
     0);
   NODE_DBG("mount res: %i\n", res);

app/spiffs/spiffs_config.h

@@ -8,16 +8,10 @@
 #ifndef SPIFFS_CONFIG_H_
 #define SPIFFS_CONFIG_H_
 
-// ----------- 8< ------------
+#include "user_config.h"
-// Following includes are for the linux test build of spiffs
-// These may/should/must be removed/altered/replaced in your target
-// #include "params_test.h"
 #include "c_stdio.h"
-#include "c_stdlib.h"
+#include "c_stdint.h"
 #include "c_string.h"
-#include "c_stddef.h"
-#include "c_types.h"
-// ----------- >8 ------------
 
 typedef sint32_t s32_t;
 typedef uint32_t u32_t;
@@ -67,6 +61,8 @@ typedef uint8_t u8_t;
 #ifndef  SPIFFS_CACHE_STATS
 #define SPIFFS_CACHE_STATS              0
 #endif
+#else
+#define SPIFFS_CACHE_WR                 0
 #endif
 
 // Always check header of each accessed page to ensure consistent state.

app/spiffs/spiffs_nucleus.h

@@ -405,7 +405,7 @@ typedef struct {
 // page header, part of each page except object lookup pages
 // NB: this is always aligned when the data page is an object index,
 // as in this case struct spiffs_page_object_ix is used
-typedef struct __attribute(( packed )) {
+typedef struct __attribute(( packed, aligned(4) )) {
   // object id
   spiffs_obj_id obj_id;
   // object span index