Allow byte access to PROGMEM without pgm_read macro

cores/esp8266/core_esp8266_main.cpp

@@ -34,6 +34,8 @@ extern "C" {
 }
 #include <core_version.h>
 #include "gdb_hooks.h"
+#include <core_esp8266_unaligned.h>
+
 
 #define LOOP_TASK_PRIORITY 1
 #define LOOP_QUEUE_SIZE    1
@@ -320,6 +322,10 @@ extern "C" void user_init(void) {
 
     cont_init(g_pcont);
 
+#ifdef UNALIGNED_HANDLER
+    install_unaligned_exception_handler();
+#endif
+
     preinit(); // Prior to C++ Dynamic Init (not related to above init() ). Meant to be user redefinable.
 
     ets_task(loop_task,

cores/esp8266/core_esp8266_unaligned.cpp

@@ -0,0 +1,90 @@
+/* Unaligned exception handler, allows for byte accesses to PROGMEM to 
+ * succeed without causing a crash.  It is still preferred to use the
+ * xxx_P macros whenever possible, since they are probably 30x faster than
+ * this exception handler method.
+ *
+ * Code taken directly from @pvvx's public domain code in
+ * https://github.com/pvvx/esp8266web/blob/master/app/sdklib/system/app_main.c
+ */
+
+#include <Arduino.h>
+#include <core_esp8266_unaligned.h>
+#include <esp8266_undocumented.h>
+#include <Schedule.h>
+#include <debug.h>
+
+
+#define LOAD_MASK   0x00f00fu
+#define L8UI_MATCH  0x000002u
+#define L16UI_MATCH 0x001002u
+#define L16SI_MATCH 0x009002u
+
+#define EXCCAUSE_LOAD_STORE_ERROR 3 // Unaligned read/write error
+
+static bool fired = false;
+static void warning(void)
+{
+    DEBUGV("WARNING: The unaligned hander has been invoked and performance may suffer.\n");
+}
+
+static ICACHE_RAM_ATTR void read_align_exception_handler(struct __exception_frame *ef, uint32_t cause)
+{
+  uint32_t epc1 = ef->epc;
+  uint32_t excvaddr;
+  uint32_t insn;
+  __asm (
+    "rsr   %0, EXCVADDR;"    /* read out the faulting address */
+    "movi  a4, ~3;"          /* prepare a mask for the EPC */
+    "and   a4, a4, %2;"      /* apply mask for 32bit aligned base */
+    "l32i  a5, a4, 0;"       /* load part 1 */
+    "l32i  a6, a4, 4;"       /* load part 2 */
+    "ssa8l %2;"              /* set up shift register for src op */
+    "src   %1, a6, a5;"      /* right shift to get faulting instruction */
+    :"=r"(excvaddr), "=r"(insn)
+    :"r"(epc1)
+    :"a4", "a5", "a6"
+  );
+
+  uint32_t valmask = 0;
+  uint32_t what = insn & LOAD_MASK;
+
+  if (what == L8UI_MATCH)
+    valmask = 0xffu;
+  else if (what == L16UI_MATCH || what == L16SI_MATCH)
+    valmask = 0xffffu;
+  else
+  {
+die:
+    /* Go to the default handler, we can't help here */
+    _xtos_unhandled_exception(ef, cause);
+  }
+
+  if (!fired) {
+    fired = true;
+    schedule_function(warning);
+  }
+
+  /* Load, shift and mask down to correct size */
+  uint32_t val = (*(uint32_t *)(excvaddr & ~0x3));
+  val >>= (excvaddr & 0x3) * 8;
+  val &= valmask;
+
+  /* Sign-extend for L16SI, if applicable */
+  if (what == L16SI_MATCH && (val & 0x8000))
+    val |= 0xffff0000;
+
+  int regno = (insn & 0x0000f0u) >> 4;
+  if (regno == 1)
+    goto die;              /* we can't support loading into a1, just die */
+  else if (regno != 0)
+    --regno;               /* account for skipped a1 in exception_frame */
+
+  ef->a_reg[regno] = val;  /* carry out the load */
+  ef->epc += 3;            /* resume at following instruction */
+}
+
+
+void install_unaligned_exception_handler()
+{
+  _xtos_set_exception_handler(EXCCAUSE_LOAD_STORE_ERROR, read_align_exception_handler);
+}

cores/esp8266/core_esp8266_unaligned.h

@@ -0,0 +1 @@
+extern void install_unaligned_exception_handler();

cores/esp8266/esp8266_undocumented.h

@@ -1,5 +1,8 @@
 // ROM and blob calls without official headers available
 
+#ifndef __ESP8266_UNDOCUMENTED_H
+#define __ESP8266_UNDOCUMENTED_H
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -34,6 +37,42 @@ extern int ets_uart_printf(const char *format, ...) __attribute__ ((format (prin
 
 extern void ets_delay_us(uint32_t us);
 
+/* The Xtensa OS code in ROM for handling hardware exceptions */
+struct __exception_frame
+{
+  uint32_t epc;
+  uint32_t ps;
+  uint32_t sar;
+  uint32_t unused;
+  union {
+    struct {
+      uint32_t a0;
+      // note: no a1 here!
+      uint32_t a2;
+      uint32_t a3;
+      uint32_t a4;
+      uint32_t a5;
+      uint32_t a6;
+      uint32_t a7;
+      uint32_t a8;
+      uint32_t a9;
+      uint32_t a10;
+      uint32_t a11;
+      uint32_t a12;
+      uint32_t a13;
+      uint32_t a14;
+      uint32_t a15;
+    };
+    uint32_t a_reg[15];
+  };
+  uint32_t cause;
+};
+
+extern void _xtos_set_exception_handler(uint32_t reason, void (*fn)(struct __exception_frame *ef, uint32_t cause));
+extern void _xtos_unhandled_exception(struct __exception_frame *ef, uint32_t cause);
+
 #ifdef __cplusplus
 };
 #endif
+
+#endif

platform.txt

@@ -33,6 +33,8 @@ build.vtable_flags=-DVTABLES_IN_FLASH
 
 build.sslflags=
 
+build.unalignedflags=
+
 build.exception_flags=-fno-exceptions
 build.stdcpp_lib=-lstdc++
 build.stdcpp_level=-std=gnu++11
@@ -53,7 +55,7 @@ compiler.libc.path={runtime.platform.path}/tools/sdk/libc/xtensa-lx106-elf
 compiler.cpreprocessor.flags=-D__ets__ -DICACHE_FLASH -U__STRICT_ANSI__ "-I{compiler.sdk.path}/include" "-I{compiler.sdk.path}/{build.lwip_include}" "-I{compiler.libc.path}/include" "-I{build.path}/core"
 
 compiler.c.cmd=xtensa-lx106-elf-gcc
-compiler.c.flags=-c {compiler.warning_flags} -Os -g -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -std=gnu99 -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags}
+compiler.c.flags=-c {compiler.warning_flags} -Os -g -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -std=gnu99 -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.unalignedflags}
 
 compiler.S.cmd=xtensa-lx106-elf-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -MMD -mlongcalls
@@ -64,7 +66,7 @@ compiler.c.elf.cmd=xtensa-lx106-elf-gcc
 compiler.c.elf.libs=-lhal -lphy -lpp -lnet80211 {build.lwip_lib} -lwpa -lcrypto -lmain -lwps -lbearssl -laxtls -lespnow -lsmartconfig -lairkiss -lwpa2 {build.stdcpp_lib} -lm -lc -lgcc
 
 compiler.cpp.cmd=xtensa-lx106-elf-g++
-compiler.cpp.flags=-c {compiler.warning_flags} -Os -g -mlongcalls -mtext-section-literals -fno-rtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags}
+compiler.cpp.flags=-c {compiler.warning_flags} -Os -g -mlongcalls -mtext-section-literals -fno-rtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.unalignedflags}
 
 compiler.as.cmd=xtensa-lx106-elf-as
 

tools/boards.txt.py

@@ -1186,6 +1186,14 @@
         ( '.menu.ssl.basic.build.sslflags', '-DBEARSSL_SSL_BASIC'),
         ]),
 
+    ######################## Unaligned exception handler
+
+    'unaligned_menu': collections.OrderedDict([
+        ('.menu.unaligned.safe', 'Allow byte and word access to PROGMEM' ),
+        ('.menu.unaligned.safe.build.unalignedflags', '-DUNALIGNED_HANDLER'),
+        ('.menu.unaligned.fast', 'Require pgm_read macros for PROGMEM' ),
+        ('.menu.unaligned.fast.build.unalignedflags', ''),
+        ])
     }
 
 ################################################################
@@ -1546,6 +1554,7 @@ def all_boards ():
     print('menu.wipe=Erase Flash')
     print('menu.sdk=Espressif FW')
     print('menu.ssl=SSL Support')
+    print('menu.unaligned=Unaligned Accesses')
     print('')
 
     missingboards = []
@@ -1564,7 +1573,7 @@ def all_boards ():
                 print(id + optname + '=' + board['opts'][optname])
 
         # macros
-        macrolist = [ 'defaults', 'cpufreq_menu', 'vtable_menu', 'exception_menu', 'ssl_cipher_menu' ]
+        macrolist = [ 'defaults', 'cpufreq_menu', 'vtable_menu', 'exception_menu', 'ssl_cipher_menu', 'unaligned_menu' ]
         if 'macro' in board:
             macrolist += board['macro']
         if lwip == 2: