core: backport TLB handling to fx9860g, fix return-to-menu (UNSTABLE)

This change ports the TLB management system to fx9860g through %003.
This raises the size limit for add-ins to about 500k.

Because SH3 fx9860g does not have ILRAM, the GMAPPED attribute has been
made to generate content to a .gint.mapped section which is sent to the
P1 RAM section historically dubbed "real ram" in which gint's data and
VBR are installed. (Now that I think about it, gint's data should try to
go to normal RAM instead to reduce pressure on this invasion.)

Return-to-menu was also fixed on both platforms by narrowing down the
need for code to remain mapped to the chance of running it with
interrupts disabled. The natural distribution of GMAPPED under this
criterion showed that _gint_setvbr had been left under TLB control;
moving it to the proper RAM area fixed gint switches.

Finally, an omission in the bound checks for mappable TEA addresses (TEA
>= 0x00300000) prevented the appearance of a non-interactible System
ERROR popup when some unmapped addresses are accessed.

This version still does not enable interrupts in timer callbacks,
exposing any application to a crash if a timer underflows while its
callback is not mapped. It is not suitable for any stable application!

fx9860g.ld

@@ -13,9 +13,8 @@ ENTRY(_start)
 
 MEMORY
 {
-	/* Userspace mapping of the add-in (0x200 B are for the G1A header).
-	   220k is the maximum amount of simultaneously-mappable code */
-	rom   (rx):   o = 0x00300200, l = 220k
+	/* Userspace mapping of the add-in (G1A header takes 0x200 bytes) */
+	rom   (rx):   o = 0x00300200, l = 500k
 	/* This is mapped to RAM; 8k on SH3, apparently 32k on SH4 */
 	ram   (rw):   o = 0x08100000, l = 8k
 	/* gint's VBR space, mentioned here for completeness */
@@ -60,9 +59,13 @@ SECTIONS
 	} > rom
 
 	.text : {
-		_gint_exch_tlbh_start = . ;
-		*(.gint.exch_tlbh);
-		_gint_exch_tlbh_size = ABSOLUTE(. - _gint_exch_tlbh_start);
+		_gint_exch_start = . ;
+		*(.gint.exch)
+		_gint_exch_size = ABSOLUTE(. - _gint_exch_start);
+
+		_gint_tlbh_start = . ;
+		*(.gint.tlbh)
+		_gint_tlbh_size = ABSOLUTE(. - _gint_tlbh_start);
 
 		*(.text .text.*)
 		*(C P)
@@ -210,6 +213,9 @@ SECTIONS
 
 		*(.gint.data .gint.data.*)
 
+		/* Also code that must remain permanently mapped! */
+		*(.gint.mapped)
+
 		. = ALIGN(16);
 	} > rram AT> rom
 
@@ -234,7 +240,7 @@ SECTIONS
 
 	/* Unwanted sections going to meet Dave Null:
 	   - Debug sections, often come out of libgcc
-	   - Java classes registration (why are there even here?)
+	   - Java classes registration (why is there any of this here?)
 	   - Asynchronous unwind tables: no C++ exception handling for now ^^
 	   - Comments or anything the compiler might put in its assembler
 	   - A stack section sometimes generated for build/version.o */

fxcg50.ld

@@ -147,6 +147,8 @@ SECTIONS
 		_rilram = . ;
 
 		*(.ilram)
+		/* Code that must remain mapped is placed here */
+		*(.gint.mapped)
 
 		. = ALIGN(16);
 	} > ilram AT> rom
@@ -224,7 +226,7 @@ SECTIONS
 	/* Unwanted sections going to meet Dave Null:
 	   - SH3-only data sections
 	   - Debug sections, often come out of libgcc
-	   - Java classes registration (why are there even here?)
+	   - Java classes registration (why is there any of this here?)
 	   - Asynchronous unwind tables: no C++ exception handling for now ^^
 	   - Comments or anything the compiler might put in its assembler */
 	/DISCARD/ : {

include/gint/defs/attributes.h

@@ -17,8 +17,9 @@
 #define GILRAM		__attribute__((section(".ilram")))
 #define GXRAM		__attribute__((section(".xram")))
 #define GYRAM		__attribute__((section(".yram")))
-/* Objects that must remain mapped */
-#define GMAPPED		GILRAM
+/* Objects that must remain mapped; placed in "real RAM" (some P1 area) on
+   fx9860g, and ILRAM on fxcg50 */
+#define GMAPPED		__attribute__((section(".gint.mapped")))
 
 /* Unused parameters or variables */
 #define GUNUSED		__attribute__((unused))

include/gint/exc.h

@@ -27,13 +27,17 @@ void gint_panic_set(GNORETURN void (*panic)(uint32_t code));
 /* gint_exc_catch(): Set a function to catch exceptions
 
    Sets up an exception-catching function. If an exception occurs, before a
-   panic is raised, the exception-catching function is executed in interrupt
+   panic is raised, the exception-catching function is executed with interrupt
    mode and is given a chance to handle the exception. Passing NULL disables
    this feature.
 
    The exception-catching function can do anything that does not use interrupts
-   or causes an exception, such as logging the exception or any other useful
-   mechanism.
+   or cause an exception, such as logging the exception or any other useful
+   mechanism. TLB misses count as exceptions and are disabled, so this function
+   must absolutely be mapped *before* it runs! The only real way to ensure this
+   is to have it mapped at all times using the GMAPPED attribute. Note that
+   GMAPPED puts the function in a generally small memory region so you should
+   defer as much handling as possible until after the exception is caught.
 
    What happens next depends on the return value:
    * If it returns 0, the exception is considered handled and execution
@@ -58,7 +62,7 @@ void gint_exc_catch(int (*handler)(uint32_t code));
    When an exception-catching function records an exception without solving it,
    this re-execution will fail again and the exception handling process will
    loop. In such a situation, gint_exc_skip() can be used to manually skip the
-   offending instruction.
+   offending instruction, if this is an acceptable resolution.
 
    @instructions  Number of instructions to skip (usually only one) */
 void gint_exc_skip(int instructions);

src/core/exch.c

@@ -9,7 +9,7 @@
 #define dtext(x, y, str)  dtext (x, y, str, C_BLACK, C_NONE)
 
 /* gint_panic_default(): Default panic handler */
-GNORETURN GMAPPED static void gint_default_panic(GUNUSED uint32_t code)
+GNORETURN static void gint_default_panic(GUNUSED uint32_t code)
 {
 	uint32_t TEA, TRA;
 
@@ -95,7 +95,7 @@ GNORETURN GMAPPED static void gint_default_panic(GUNUSED uint32_t code)
 	dprint(38, 75, "= %#x", TRA);
 	dtext(281, 75, "(Trap number)");
 
-	dtext(6, 95,  "An unrecoverable error ocurred in the add-in.");
+	dtext(6, 95,  "An unrecoverable error occurred in the add-in.");
 	dtext(6, 108, "Please press the RESET button to restart the");
 	dtext(6, 121, "calculator.");
 
@@ -124,7 +124,7 @@ GDATA GNORETURN void (*gint_exc_panic)(uint32_t code) = gint_default_panic;
 GDATA int (*gint_exc_catcher)(uint32_t code) = NULL;
 
 /* gint_panic(): Panic handler function */
-GMAPPED void gint_panic(uint32_t code)
+void gint_panic(uint32_t code)
 {
 	gint_exc_panic(code);
 }

src/core/setup.c

@@ -14,7 +14,7 @@
 /* VBR address, from the linker script */
 extern char gint_vbr[];
 /* System's VBR address */
-GBSS uint32_t system_vbr;
+GBSS static uint32_t system_vbr;
 /* Size of exception and TLB handler */
 extern char gint_exch_size;
 extern char gint_tlbh_size;
@@ -95,7 +95,7 @@ GMAPPED static void lock(void)
 }
 
 /* gint_install() - install and start gint */
-GMAPPED void gint_install(void)
+void gint_install(void)
 {
 	/* VBR address, provided by the linker script */
 	void *vbr = (void *)&gint_vbr;
@@ -135,7 +135,7 @@ GMAPPED static void unlock(void)
 }
 
 /* gint_unload() - unload gint and give back control to the system */
-GMAPPED void gint_unload(void)
+void gint_unload(void)
 {
 	/* First wait for all the drivers to finish their current jobs */
 	for(gint_driver_t *drv = &edrv; (--drv) >= &bdrv;)
@@ -192,7 +192,7 @@ GMAPPED static void gint_switch_in(void)
 }
 
 /* gint_switch() - temporarily switch out of gint */
-GMAPPED void gint_switch(void (*function)(void))
+void gint_switch(void (*function)(void))
 {
 	/* Wait for all the drivers to finish their current jobs */
 	for(gint_driver_t *drv = &edrv; (--drv) >= &bdrv;)
@@ -203,18 +203,6 @@ GMAPPED void gint_switch(void (*function)(void))
 	gint_setvbr(system_vbr, gint_switch_out);
 	if(function) function();
 
-	/* Remap all of the ROM */
-	extern uint32_t brom, srom;
-	volatile void *b = &brom;
-	int32_t s = (int32_t)&srom;
-	GUNUSED uint8_t x;
-	while(s > 0)
-	{
-		x = *(volatile uint8_t *)b;
-		b += 1024;
-		s -= 1024;
-	}
-
 	/* Wait for the OS to finish working */
 	for(gint_driver_t *drv = &edrv; (--drv) >= &bdrv;)
 	{
@@ -235,7 +223,7 @@ void  __ConfigureStatusArea(int mode);
 
 static int __osmenu_id;
 
-GMAPPED static void __osmenu_handler(void)
+static void __osmenu_handler(void)
 {
 	__PutKeyCode(0x04, 0x09, 0);
 
@@ -243,7 +231,7 @@ GMAPPED static void __osmenu_handler(void)
 	__Timer_Deinstall(__osmenu_id);
 }
 
-GMAPPED static void __osmenu(void)
+static void __osmenu(void)
 {
 	__ClearKeyBuffer();
 
@@ -288,7 +276,7 @@ GMAPPED static void __osmenu(void)
 }
 
 /* gint_osmenu() - switch out of gint and call the calculator's main menu */
-GMAPPED void gint_osmenu(void)
+void gint_osmenu(void)
 {
 	gint_switch(__osmenu);
 }

src/core/start.c

@@ -93,10 +93,11 @@ int start(int isappli, int optnum)
 	   redirecting interrupts and reimplementing drivers, so we can't rely
 	   too much on the system. Ladies and gentlemen, let's have fun! ;D */
 
-	/* For now, we use the system's memory mapper for ROM. RAM is always
+	/* For now, we use the system's memory mapper for ROM. We'll still do
+	   it from our TLB miss handler once we're installed. RAM is always
 	   fully mapped, but we need to initialize it. We also need to do some
 	   hardware detection because old fx9860g models have a different
-	   processor with some incompatible features */
+	   processor with some incompatible features. */
 
 	/* Detect architecture - this will tell SH3 from SH4 on fx9860g */
 	hw_detect();
@@ -118,7 +119,7 @@ int start(int isappli, int optnum)
 	/* We are now running on our own in kernel mode. Since we have taken
 	   control of interrupts, pretty much any interaction with the system
 	   will break it. We'll limit our use of syscalls and do device driving
-	   ourselves. (Hopefully we can add cool features in the process.) */
+	   ourselves. (Hopefully we can add cool features in the process!) */
 
 	gint_driver_t *drv;
 

src/core/syscalls.S

@@ -51,9 +51,9 @@
 
 #define syscall(id) syscall_(id, syscall_table)
 
-/*** Special syscalls in ILRAM ***/
+/*** Special syscalls that must remain mapped ***/
 
-.section .ilram
+.section .gint.mapped
 
 #ifdef FX9860G
 ___TLB_LoadPTEH:

src/core/tlbh.S

@@ -17,14 +17,17 @@ _gint_tlbh:
 	mov.l	.tea_sh3, r0
 
 test_tea:
-	# Check TEA to see if we want to map a page or raise a SysERROR
+	/* Check TEA to see if we want to map a page or raise a SysERROR */
 	mov.l	@r0, r0
 	mov.l	.max_mapped_rom, r1
 	cmp/ge	r1, r0
 	bt	panic
+	mov.l	.min_mapped_rom, r1
+	cmp/ge	r1, r0
+	bf	panic
 
 map:
-	# If TEA is mappable, map a page and return
+	/* If TEA is mappable, map a page and return */
 	mov.l	.TLB_LoadPTEH, r0
 	jsr	@r0
 	nop
@@ -37,8 +40,8 @@ map:
 	nop
 
 panic:
-	# Otherwise, panic by defaulting to the exception handler (the TLB miss
-	# may still be resolved by a panic handler)
+	/* Otherwise, panic by defaulting to the exception handler (the TLB
+	   miss may still be resolved by a panic handler) */
 	lds.l	@r15+, macl
 	lds.l	@r15+, mach
 	ldc.l	@r15+, gbr
@@ -59,6 +62,8 @@ panic:
 	.long	0xff00000c
 .tea_sh3:
 	.long	0xfffffffc
+.min_mapped_rom:
+	.long	0x00300000
 .max_mapped_rom:
 	.long	0x00300000 + _srom
 .TLB_LoadPTEH:

src/core/vbr.s

@@ -2,9 +2,8 @@
 **	gint:core:vbr - Assembler-level VBR management
 */
 
-	.global	_gint_setvbr
-	.text
-	.align 2
+.global	_gint_setvbr
+.section .gint.mapped
 
 /* gint_setvbr()
    Changes the VBR address and the calls the configuration function while