added facility to debug the stack pointer on P3_4 (LCD LED cathode)

roughly 139 bytes
functions were chosen by manually traversing pow_decn to the bottom

Makefile

@@ -4,8 +4,9 @@ SDCCOPTS ?= --code-size $(STCCODESIZE) --xram-size 256 --idata-loc 0x80
 #SDCCOPTS ?= --code-size $(STCCODESIZE) --xram-size 256 --stack-auto --model-large
 FLASHFILE ?= main.hex
 LARGE_LDFLAGS += -L/usr/share/sdcc/lib/large/
+# CFLAGS += -DSTACK_DEBUG # write the stack pointer to P3_4
 
-SRC = src/lcd.c src/key.c src/utils.c src/decn/decn.c src/calc.c
+SRC = src/lcd.c src/key.c src/utils.c src/decn/decn.c src/calc.c src/stack_debug.c
 
 OBJ=$(patsubst src%.c,build%.rel, $(SRC))
 
@@ -13,7 +14,7 @@ all: main
 
 build/%.rel: src/%.c src/%.h
 	mkdir -p $(dir $@)
-	$(SDCC) $(SDCCOPTS) -o $@ -c $<
+	$(SDCC) $(SDCCOPTS) $(CFLAGS) -o $@ -c $<
 
 main: $(OBJ)
 	$(SDCC) -o build/ src/$@.c $(SDCCOPTS) $(CFLAGS) $^
@@ -21,7 +22,7 @@ main: $(OBJ)
 	@ tail -n 5 build/main.mem | head -n 2
 	@ tail -n 1 build/main.mem
 	cp build/$@.ihx $@.hex
-	
+
 eeprom:
 	sed -ne '/:..1/ { s/1/0/2; p }' main.hex > eeprom.hex
 

src/calc.c

@@ -21,6 +21,7 @@
 #include "utils.h"
 
 #include "calc.h"
+#include "stack_debug.h"
 
 __xdata dec80 StoredDecn;
 __xdata dec80 LastX;

src/decn/CMakeLists.txt

@@ -12,7 +12,7 @@ target_compile_options(coverage_config INTERFACE -O0 -g --coverage)
 target_link_libraries(coverage_config INTERFACE --coverage)
 
 # decn library
-add_library(decn decn.c)
+add_library(decn decn.c ../utils.c)
 
 # decn library with coverage
 add_library(decn_cover decn.c)

src/decn/decn.c

@@ -19,6 +19,7 @@
  */
 
 #include "../utils.h"
+#include "../stack_debug.h"
 
 #include "decn.h"
 
@@ -86,6 +87,8 @@ const dec80 DECN_LN_10 = {
 
 void copy_decn(dec80* const dest, const dec80* const src){
 	uint8_t i;
+
+	stack_debug(0x01);
 	dest->exponent = src->exponent;
 
 	//copy nibbles
@@ -163,6 +166,7 @@ static void remove_leading_zeros(dec80* x){
 	uint8_t is_negative = (x->exponent < 0);
 	exp_t exponent = get_exponent(x);
 
+	stack_debug(0x02);
 	//find first non-zero digit100
 	for (digit100 = 0; digit100 < DEC80_NUM_LSU; digit100++){
 		if (x->lsu[digit100] != 0){

src/lcd.c

@@ -155,9 +155,15 @@ void LCD_Open(void) {
 	//P2 entire port
 	P2M1 = 0;
 	P2M0 = 0xff;
+#ifdef STACK_DEBUG
+	// P3_4 is special
+	P3M1 &= ~(0xe0);
+	P3M0 |= (0xe0);
+#else
 	//P3 pins 7:4
 	P3M1 &= ~(0xf0);
 	P3M0 |= (0xf0);
+#endif
 
 	_delay_ms(30); // to allow LCD powerup
 	outCsrBlindNibble(0x03); // (DL=1 8-bit mode)

src/main.c

@@ -28,6 +28,7 @@
 #else
 #include "stc15.h"
 #endif
+#include "stack_debug.h"
 
 #define FOSC 11583000
 
@@ -225,7 +226,9 @@ int main()
 	LCD_Open();
 	KeyInit();
 	Timer0Init(); //for reading keyboard
-	BACKLIGHT_ON(); //turn on led backlight
+	backlight_on(); //turn on led backlight
+	stack_debug_init();
+	stack_debug(0xfe);
 
 	ExpBuf[0] = 0;
 	ExpBuf[1] = 0;
@@ -529,7 +532,7 @@ int main()
 		LcdAvailable.release();
 #endif
 		//turn backlight back on
-		BACKLIGHT_ON();
+		backlight_on();
 	} //while (1)
 }
 /* ------------------------------------------------------------------------- */

src/stack_debug.c

@@ -0,0 +1,92 @@
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#include <stdint.h>
+#include "stack_debug.h"
+
+#if defined(STACK_DEBUG)
+extern uint16_t _SP;
+
+inline static void HIGH() {
+	P3_4 = 1;
+}
+
+inline static void LOW() {
+	P3_4 = 1;
+}
+
+void stack_debug_init() {
+	P3M1 &= ~(0x10);
+	P3M0 |= 0x10;
+	LOW();
+	stack_debug_write(0x55);
+	stack_debug_write(0xAA);
+	stack_debug_write(0x55);
+	stack_debug_write(0xAA);
+	stack_debug_write(0x80);
+	stack_debug_write(0x10);
+	stack_debug_write(0x08);
+	stack_debug_write(0x01);
+}
+
+/*
+  for frequency of 12.000 MHz (12.005 adjusted) this gives a rate of 1'190'000 Baud
+  negative polarity, MSB
+ */
+
+void stack_debug_write(uint8_t value) __naked {
+	value;
+__asm
+	.macro HIGH
+	setb _P3_4
+	.endm
+
+	.macro LOW
+	clr _P3_4
+	.endm
+
+	mov   dph,r0
+	mov   a,dpl
+	mov   r0,#8
+	; START
+	HIGH                    ; 1
+	nop                     ; 1
+	nop                     ; 1
+	nop                     ; 1
+stack_debug_1$:
+	rlc   a                 ; 1
+	jc    stack_debug_2$    ; 3
+	HIGH                    ; 1
+	djnz  r0,stack_debug_1$ ; 4
+	sjmp  stack_debug_3$    ; 3
+stack_debug_2$:
+	LOW                     ; 1
+	djnz  r0,stack_debug_1$ ; 4
+	sjmp  stack_debug_3$    ; 3
+stack_debug_3$:
+	nop                     ; 1
+        ; STOP
+	LOW                     ; 1
+	nop                     ; 1
+	nop                     ; 1
+
+	mov   r0,dph            ; 3
+	ret                     ; 4
+__endasm;
+}
+
+void stack_debug(uint8_t marker) {
+	stack_debug_write(marker);
+	stack_debug_write(SP);
+}
+#endif // !defined(DESKTOP)

src/stack_debug.h

@@ -0,0 +1,54 @@
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#ifndef SRC_STACK_DEBUG_H_
+#define SRC_STACK_DEBUG_H_
+
+#include <stdint.h>
+
+#if !defined(DESKTOP)
+#include "stc15.h"
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// P3_4 is connected to the cathode and the only pin that is not toggled normally
+// unfortunately, the hardware uart cannot be mapped to TX = P3_4
+
+#if defined(STACK_DEBUG)
+void stack_debug_init(void);
+void stack_debug(uint8_t marker);
+void stack_debug_write(uint8_t value) __naked;
+#else
+#define stack_debug_init()
+#define stack_debug(marker)
+#endif
+
+#if defined(DESKTOP) || defined(STACK_DEBUG)
+#define backlight_on()
+#define backlight_off()
+#else
+inline void backlight_on(void) {
+	P3_4 = 0;
+}
+inline void backlight_off(void) {
+	P3_4 = 1;
+}
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

src/utils.c

@@ -29,7 +29,6 @@ void _delay_us(uint8_t us)
 	(void) us;
 }
 #endif
-void backlight_off(void){ }
 #else //!DESKTOP
 void _delay_ms(uint8_t ms)
 {
@@ -69,10 +68,6 @@ void _delay_us(uint8_t us)
 }
 #endif
 
-void backlight_off(void){
-	P3_4 = 1;
-}
-
 #endif //ifdef desktop
 
 #ifdef DESKTOP

src/utils.h

@@ -35,9 +35,6 @@ void _delay_us(uint8_t us);
 #define _delay_us(x) _delay_ms(1)
 #endif
 
-void backlight_off(void);
-
-
 
 #ifdef __linux__
 #define DESKTOP
@@ -58,11 +55,9 @@ char* u32str(uint32_t x, char* buf, uint8_t base);
 #define __at uint8_t*
 #define SDCC_ISR(isr, reg)
 #define __using(x)
-#define BACKLIGHT_ON()
 #define TURN_OFF()
 #else
 #define SDCC_ISR(isr, reg) __interrupt (isr) __using (reg)
-#define BACKLIGHT_ON()  P3_4 = 0
 #define TURN_OFF() P3_2 = 0
 #endif