From 59c60504e7a873ecd9bea41e879cd72bc96156ba Mon Sep 17 00:00:00 2001
From: d00f <8052722+DrDoof@users.noreply.github.com>
Date: Sat, 15 Aug 2026 17:41:34 +0200
Subject: [PATCH] crtbank: put the bank switching helpers in HOME

__sdcc_banked_call and __sdcc_banked_ret were assembled into GSFINAL, which
sits in the startup path: GSINIT ends exactly where GSFINAL begins, so the
processor falls into it rather than being sent there. It works today only
because this object comes after every C object on the link line, so the
LJMP to __sdcc_program_startup is laid down first and the helpers land
behind it. Reordering that line, or moving main() into another module,
would put the helper body at the fallthrough address instead, and the board
would not come up out of a build that reports nothing wrong.

SDCC's own crtbank.asm declares the area order and then puts both symbols
in HOME, so the file takes that name and that preamble as well.

GSFINAL now holds the three byte jump and nothing else. Of 401 symbols 17
change address, every one in the startup region, and between the reset
vector and 0x0094 not a byte differs, so no interrupt vector is disturbed.

Run on a SWTGW218AS: it came back after about 42 seconds reporting the new
build, with its stored configuration byte identical and every link at the
speed it had before.
---
 Makefile     |  2 +-
 crtbank.asm  | 29 +++++++++++++++++++++++++++++
 crtstart.asm | 17 -----------------
 3 files changed, 30 insertions(+), 18 deletions(-)
 create mode 100644 crtbank.asm
 delete mode 100644 crtstart.asm

diff --git a/Makefile b/Makefile
index 9ab0da8..4044551 100644
--- a/Makefile
+++ b/Makefile
@@ -118,7 +118,7 @@ $(BUILDDIR)/%.rel: %.asm
 	${ASM} ${AFLAGS} -o $@ $<
 #	mv -f $(addprefix $(basename $^), .lst .rel .sym) .
 
-$(BUILDDIR)/rtlplayground.ihx: $(OBJS) $(BUILDDIR)/crtstart.rel $(BUILDDIR)/crc16.rel
+$(BUILDDIR)/rtlplayground.ihx: $(OBJS) $(BUILDDIR)/crtbank.rel $(BUILDDIR)/crc16.rel
 	$(CC) $(CC_FLAGS) -Wl-bHOME=0x00000 -Wl-bBANK1=0x14000 -Wl-bBANK2=0x24000 -Wl-r -o $@ $^
 
 $(BUILDDIR)/rtlplayground.img: $(BUILDDIR)/rtlplayground.ihx
diff --git a/crtbank.asm b/crtbank.asm
new file mode 100644
index 0000000..7a00868
--- /dev/null
+++ b/crtbank.asm
@@ -0,0 +1,29 @@
+	.area HOME    (CODE)
+	.area GSINIT0 (CODE)
+	.area GSINIT1 (CODE)
+	.area GSINIT2 (CODE)
+	.area GSINIT3 (CODE)
+	.area GSINIT4 (CODE)
+	.area GSINIT5 (CODE)
+	.area GSINIT  (CODE)
+	.area GSFINAL (CODE)
+	.area CSEG    (CODE)
+
+
+	.area HOME    (CODE)
+
+__sdcc_banked_call::
+	push	_PSBANK
+	xch	a,r0
+	push	a
+	mov	a,r1
+	push	a
+	mov	a,r2
+	anl	a,#0x1f
+	mov	_PSBANK, a
+	xch	a, r0
+	ret
+
+__sdcc_banked_ret::
+	pop	_PSBANK
+	ret
diff --git a/crtstart.asm b/crtstart.asm
deleted file mode 100644
index 23146a7..0000000
--- a/crtstart.asm
+++ /dev/null
@@ -1,17 +0,0 @@
-	.area GSFINAL (CODE)
-
-__sdcc_banked_call::
-	push	_PSBANK
-	xch	a,r0
-	push	a
-	mov	a,r1
-	push	a
-	mov	a,r2
-	anl	a,#0x1f
-	mov	_PSBANK, a
-	xch	a, r0
-	ret
-
-__sdcc_banked_ret::
-	pop	_PSBANK
-	ret