basics: Add an example on UNROM

Signed-off-by: Miquel Sabaté Solà <msabate@suse.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/config/unrom.cfg b/config/unrom.cfg
new file mode 100644
index 0000000..5b18707
--- /dev/null
+++ b/config/unrom.cfg
@@ -0,0 +1,58 @@
+##
+# This is a very minimalistic linker configuration for UNROM chips. This
+# configuration assumes the standard UNROM configuration, with two regions
+# defined that split $8000-$FFFF, where the first half is swappable. For the
+# bank switching there are 7 banks, which coupled with the fixed region it sums
+# up 128KB of total PRG-ROM.
+#
+# NOTE: it assumes that only assembly is being used, and thus a lot of magic
+# required for C programs is missing.
+# NOTE: it is following the example of games such as Castlevania or Megaman.
+# Thus, there is no CHR segment because it's all done through RAM.
+
+MEMORY {
+    # iNES header.
+    HEADER: start = $0, size = $10, fill = yes;
+
+    # Program RAM. Available if a battery-backed RAM was requested.
+    WRAM: start = $6000, size = $2000, define = yes;
+
+    # Swappable ROM addresses. Note the filled values. This is done so it's also
+    # clear by inspecting the memory which bank we are on. This can come in
+    # handy when inspecting things with an hex editor.
+    PRG0: start = $8000, size = $4000, fill = yes, fillval = $f8, define = yes;
+    PRG1: start = $8000, size = $4000, fill = yes, fillval = $f9, define = yes;
+    PRG2: start = $8000, size = $4000, fill = yes, fillval = $fa, define = yes;
+    PRG3: start = $8000, size = $4000, fill = yes, fillval = $fb, define = yes;
+    PRG4: start = $8000, size = $4000, fill = yes, fillval = $fc, define = yes;
+    PRG5: start = $8000, size = $4000, fill = yes, fillval = $fd, define = yes;
+    PRG6: start = $8000, size = $4000, fill = yes, fillval = $fe, define = yes;
+
+    # Fixed ROM address.
+    PRG: start = $C000, size = $4000, fill = yes, fillval = $ff, define = yes;
+}
+
+SEGMENTS {
+    # iNES header.
+    HEADER: load = HEADER, type = ro;
+
+    # This is the fixed bank, that spans $C000-$FFFF. Make sure to put the reset
+    # code and basic stuff that you don't want ever to be gone here. This will
+    # include stuff like the reset code, bank switching utilities, etc.
+    FIXED: load = PRG, type = ro, define = yes;
+
+    ##
+    # Swappable banks.
+
+    BANK0: load = PRG0, type = ro, define = yes;
+    BANK1: load = PRG1, type = ro, define = yes;
+    BANK2: load = PRG2, type = ro, define = yes;
+    BANK3: load = PRG3, type = ro, define = yes;
+    BANK4: load = PRG4, type = ro, define = yes;
+    BANK5: load = PRG5, type = ro, define = yes;
+    BANK6: load = PRG6, type = ro, define = yes;
+
+    # Last but not least, the vectors must be the last thing and they are
+    # expecting a very special place on the fixed bank.
+    VECTORS: load = PRG, start = $fffa, type = ro;
+}