Examples: new sram bank pragma example

- Minor related docs updates

docs/pages/05_banking_mbcs.md

@@ -63,6 +63,7 @@ Note: You can use the `NONBANKED` keyword to define a function as non-banked if
 
 ## Setting the Cart SRAM bank for a Source file
   - `#pragma dataseg DATA_<N>` at the start of a source file. Example (Cartridge SRAM bank 3): `#pragma bank 3`
+    - See the cross-platform `sram_banks` example
   - Using the lcc switch for Cartridge SRAM bank `-Wf-ba<N>`. Example (Cartridge SRAM bank 3): `-Wf-ba3`
 
 
@@ -83,8 +84,7 @@ The MBC settings below are available when using the makebin `-Wl-yt<N>` switch.
 
 Source: Pandocs. Additional details available at [Pandocs](https://gbdev.io/pandocs/The_Cartridge_Header.html#0147---cartridge-type "Pandocs")
 
-For SMS/GG, the ROM file size must be at least 64K to enable mapper support for Cart SRAM banks in emulators.
-  - If the generated ROM is too small then `-yo 4` for makebin (or `-Wm-yo4` for LCC) can be used to set the size to 64K.
+See the note about @ref gg_sms_cart_sram_info "enabling Cart SRAM and number of banks available for SMS/GG"
 
 
 ## MBC Type Chart
@@ -355,6 +355,7 @@ There are several projects in the GBDK 2020 examples folder which demonstrate di
 @anchor sms_gg_banking "SMS/GG Banking" section.
 # SMS/Game Gear Banking
 
+## ROM Banks
 The memory banking setup for SMS and Game Gear in GBDK is different than it is for the Game Boy. Instead of a single switchable bank in the `0x4000 - 0x7FFF` range, there are two switchable frames at different address ranges. The configuration is as follows:
 
 - Frame 0: Non-banked, at address `0x0000 - 0x3FFF`
@@ -370,6 +371,16 @@ The memory banking setup for SMS and Game Gear in GBDK is different than it is f
         
 Banked code and any pointers associated with it will only work correctly when active in Frame 1 (at `0x4000`), so it must use `CODE_<N>`. Graphics and other assets may go in either Frame 1 (at `0x4000`) or, if designed for it then Frame 2 (at `0x8000`).
 
+@anchor gg_sms_cart_sram_info "SMS/GG Cart SRAM info"
+## Cart SRAM Banks
+The maximum supported number of Cart SRAM banks for SMS/GG is 2. The size is 8K.
+  - Additional details in the SMS Power docs: https://www.smspower.org/Development/Mappers#RAMMapping
+
+For SMS/GG, the ROM file size must be at least 64K to enable mapper support for Cart SRAM banks in emulators.
+  - If the generated ROM is too small then `-yo 4` for makebin (or `-Wm-yo4` for LCC) can be used to set the size to 64K.
+  - If auto-banking is being used and Cart SRAM banks are specified then @ref makebin will auto-increase the ROM size to 64k to ensure
+
+
 ## Auto-Banking
 CODE and LIT cannot share the same bank number. For example, if `CODE` is assigned to `bank 3` then `LIT` cannot be in `bank 3` as well. 
 
@@ -381,3 +392,12 @@ CODE and LIT cannot share the same bank number. For example, if `CODE` is assign
 The bankpack option `-banktype=` may be used to set a bank to use specific type (`CODE` or `LIT`). This will take effect before bankpack tries to perform any bank assignment. For example: `-banktype=2:LIT` (or `-Wb-banktype=2:LIT` when used with @ref lcc) sets bank 2 to exclusively use type `LIT`.
 
 
+@anchor nes_banking "NES Banking" section.
+# NES Banking
+
+## ROM Banks
+To do
+
+@anchor nes_cart_sram_info "NES Cart SRAM info"
+## Cart SRAM Banks
+Cart SRAM is not currently supported for the NES

gbdk-lib/examples/cross-platform/sram_banks/Makefile

@@ -0,0 +1,88 @@
+SHELL := /bin/bash
+
+# If you move this project you can change the directory
+# to match your GBDK root directory (ex: GBDK_HOME = "C:/GBDK/"
+ifndef GBDK_HOME
+	GBDK_HOME = ../../../
+endif
+
+LCC = $(GBDK_HOME)bin/lcc
+
+# Set platforms to build here, spaced separated. (These are in the separate Makefile.targets)
+# They can also be built/cleaned individually: "make gg" and "make gg-clean"
+# Possible are: gb gbc pocket megaduck sms gg
+TARGETS=gb sms gg # nes
+
+# Configure platform specific LCC flags here:
+LCCFLAGS_gb      = -Wl-yt0x1B # Set an MBC for banking (1B-ROM+MBC5+RAM+BATT)
+LCCFLAGS_pocket  = -Wl-yt0x1B # Usually the same as required for .gb
+LCCFLAGS_duck    = -Wl-yt0x1B # Usually the same as required for .gb
+LCCFLAGS_gbc     = -Wl-yt0x1B -Wm-yc # Same as .gb with: -Wm-yc (gb & gbc) or Wm-yC (gbc exclusive)
+LCCFLAGS_sms     =
+LCCFLAGS_gg      =
+LCCFLAGS_nes     =
+
+LCCFLAGS += $(LCCFLAGS_$(EXT)) # This adds the current platform specific LCC Flags
+
+LCCFLAGS += -Wl-j -Wm-yoA -Wm-ya4 -autobank -Wb-ext=.rel -Wb-v # MBC + Autobanking related flags
+
+# GBDK_DEBUG = ON
+ifdef GBDK_DEBUG
+	LCCFLAGS += -debug -v
+endif
+
+
+# You can set the name of the ROM file here
+PROJECTNAME = sram_banks
+
+# EXT?=gb # Only sets extension to default (game boy .gb) if not populated
+SRCDIR      = src
+OBJDIR      = obj/$(EXT)
+RESDIR      = res
+BINDIR      = build/$(EXT)
+MKDIRS      = $(OBJDIR) $(BINDIR) # See bottom of Makefile for directory auto-creation
+
+BINS	    = $(OBJDIR)/$(PROJECTNAME).$(EXT)
+CSOURCES    = $(foreach dir,$(SRCDIR),$(notdir $(wildcard $(dir)/*.c))) $(foreach dir,$(RESDIR),$(notdir $(wildcard $(dir)/*.c)))
+ASMSOURCES  = $(foreach dir,$(SRCDIR),$(notdir $(wildcard $(dir)/*.s)))
+OBJS        = $(CSOURCES:%.c=$(OBJDIR)/%.o) $(ASMSOURCES:%.s=$(OBJDIR)/%.o)
+
+# Builds all targets sequentially
+all: $(TARGETS)
+
+# Compile .c files in "src/" to .o object files
+$(OBJDIR)/%.o:	$(SRCDIR)/%.c
+	$(LCC) $(LCCFLAGS) $(CFLAGS) -c -o $@ $<
+
+# Compile .c files in "res/" to .o object files
+$(OBJDIR)/%.o:	$(RESDIR)/%.c
+	$(LCC) $(LCCFLAGS) $(CFLAGS) -c -o $@ $<
+
+# Compile .s assembly files in "src/" to .o object files
+$(OBJDIR)/%.o:	$(SRCDIR)/%.s
+	$(LCC) $(LCCFLAGS) $(CFLAGS) -c -o $@ $<
+
+# If needed, compile .c files in "src/" to .s assembly files
+# (not required if .c is compiled directly to .o)
+$(OBJDIR)/%.s:	$(SRCDIR)/%.c
+	$(LCC) $(LCCFLAGS) $(CFLAGS) -S -o $@ $<
+
+# Link the compiled object files into a .gb ROM file
+$(BINS):	$(OBJS)
+	$(LCC) $(LCCFLAGS) $(CFLAGS) -o $(BINDIR)/$(PROJECTNAME).$(EXT) $(OBJS)
+
+clean:
+	@echo Cleaning
+	@for target in $(TARGETS); do \
+		$(MAKE) $$target-clean; \
+	done
+
+# Include available build targets
+include Makefile.targets
+
+
+# create necessary directories after Makefile is parsed but before build
+# info prevents the command from being pasted into the makefile
+ifneq ($(strip $(EXT)),)           # Only make the directories if EXT has been set by a target
+$(info $(shell mkdir -p $(MKDIRS)))
+endif

gbdk-lib/examples/cross-platform/sram_banks/Makefile.targets

@@ -0,0 +1,54 @@
+
+# Platform specific flags for compiling (only populate if they're both present)
+ifneq ($(strip $(PORT)),)
+ifneq ($(strip $(PLAT)),)
+CFLAGS += -m$(PORT):$(PLAT)
+endif
+endif
+
+# Called by the individual targets below to build a ROM
+build-target: $(BINS)
+
+clean-target:
+	rm -rf $(OBJDIR)
+	rm -rf $(BINDIR)
+
+gb-clean:
+	${MAKE} clean-target EXT=gb
+gb:
+	${MAKE} build-target PORT=sm83 PLAT=gb EXT=gb
+
+
+gbc-clean:
+	${MAKE} clean-target EXT=gbc
+gbc:
+	${MAKE} build-target PORT=sm83 PLAT=gb EXT=gbc
+
+
+pocket-clean:
+	${MAKE} clean-target EXT=pocket
+pocket:
+	${MAKE} build-target PORT=sm83 PLAT=ap EXT=pocket
+
+
+megaduck-clean:
+	${MAKE} clean-target EXT=duck
+megaduck:
+	${MAKE} build-target PORT=sm83 PLAT=duck EXT=duck
+
+
+sms-clean:
+	${MAKE} clean-target EXT=sms
+sms:
+	${MAKE} build-target PORT=z80 PLAT=sms EXT=sms
+
+
+gg-clean:
+	${MAKE} clean-target EXT=gg
+gg:
+	${MAKE} build-target PORT=z80 PLAT=gg EXT=gg
+
+nes-clean:
+	${MAKE} clean-target EXT=nes
+nes:
+	${MAKE} build-target PORT=mos6502 PLAT=nes EXT=nes

gbdk-lib/examples/cross-platform/sram_banks/src/main.c

@@ -0,0 +1,30 @@
+#include <gbdk/platform.h>
+#include <stdint.h>
+#include <stdio.h>
+
+extern int sram_bank_var_0;  /* In Cart SRAM bank 0 */
+extern int sram_bank_var_1;  /* In Cart SRAM bank 1 */
+
+void main(void)
+{
+  puts("Vars in \n"
+       "Cart SRAM Banks\n\n"
+       "Assigned using\n\n"
+       " #pragma\n"
+       " dataseg DATA_<n>\n"
+       );
+
+  ENABLE_RAM;
+
+  SWITCH_RAM(0);
+  sram_bank_var_0 = 0;
+  SWITCH_RAM(1);
+  sram_bank_var_1 = 1;
+  SWITCH_RAM(2);
+
+  SWITCH_RAM(0);
+  printf("sram_bank_var0 is %u\n", sram_bank_var_0);
+  
+  SWITCH_RAM(1);
+  printf("sram_bank_var1 is %u\n", sram_bank_var_1);
+}

gbdk-lib/examples/cross-platform/sram_banks/src/sram_bank0.c

@@ -0,0 +1,7 @@
+#include <gbdk/platform.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#pragma dataseg DATA_0  // Sets Cart SRAM bank to 0
+
+int sram_bank_var_0;  /* In Cart SRAM bank 0 */

gbdk-lib/examples/cross-platform/sram_banks/src/sram_bank1.c

@@ -0,0 +1,7 @@
+#include <gbdk/platform.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#pragma dataseg DATA_1  // Sets Cart SRAM bank to 1
+
+int sram_bank_var_1;  /* In Cart SRAM bank 1 */