1 files changed, 78 insertions, 0 deletions
diff --git a/gitlab/issues_text/target_avr/host_missing/accel_missing/1525 b/gitlab/issues_text/target_avr/host_missing/accel_missing/1525
new file mode 100644
index 000000000..aec01b592
--- /dev/null
+++ b/gitlab/issues_text/target_avr/host_missing/accel_missing/1525
@@ -0,0 +1,78 @@
+Wrong initial value of stack pointer on AVR devices
+Description of problem:
+The initial value of stack pointer of AVR MCUs should be RAMEND (address of the end of their RAM), but QEMU initialize them to 0.
+
+`qemu-system-avr -machine help` lists 4 flavors of MCUs which are ATmega168, ATmega2560, ATmega1280, ATmega328P. According to their datasheets, the stack pointer should be initialized as follows on reset.
+
+- [ATmega168](https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-9365-Automotive-Microcontrollers-ATmega88-ATmega168_Datasheet.pdf#page=12): RAMEND (which is 0x04FF)
+- [ATmega2560 and ATmega1280](https://ww1.microchip.com/downloads/en/devicedoc/atmel-2549-8-bit-avr-microcontroller-atmega640-1280-1281-2560-2561_datasheet.pdf#page=15): RAMEND (which is 0x21FF)
+- [ATmega328P](https://ww1.microchip.com/downloads/aemDocuments/documents/MCU08/ProductDocuments/DataSheets/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061B.pdf#page=22): RAMEND (which is 0x08FF)
+Steps to reproduce:
+1. Assemble the assembly code below: `avrasm2 -fI test.asm`
+
+    ```asm
+    ;; test.asm
+    .INCLUDE "m328Pdef.inc"
+
+    .EQU F_CPU = 16000000
+    .EQU BAUD_RATE = 9600
+    .EQU PRESCALE = (F_CPU / (16 * BAUD_RATE)) - 1
+
+    .CSEG
+    start:
+    	;; initialize USART (serial port)
+    	LDI R16, LOW(PRESCALE)
+    	LDI R17, HIGH(PRESCALE)
+    	STS UBRR0L, R16
+    	STS UBRR0H, R17
+    	LDI R16, (1 << RXEN0) | (1 << TXEN0)
+    	STS UCSR0B, R16
+
+    	;; Get stack pointer low byte and print it in ASCII
+    	IN R16, SPL
+    	LDI R17, 0x30
+    	ADD R16, R17
+    print1:
+    	LDS r17, UCSR0A
+    	SBRS r17, UDRE0
+    	RJMP print1
+    	STS UDR0, r16
+
+    	;; Get stack pointer high byte and print it in ASCII
+    	IN R16, SPH
+    	LDI R17, 0x30
+    	ADD R16, R17
+    print2:
+    	LDS r17, UCSR0A
+    	SBRS r17, UDRE0
+    	RJMP print2
+    	STS UDR0, r16
+
+    end:
+    	RJMP end
+    ```
+
+2. Convert it to bin file: `avr-objcopy --input-target=ihex --output-target=binary test.hex test.bin`
+
+3. Run it with QEMU: `qemu-system-avr -machine uno -bios test.bin -serial stdio`
+
+This should print 00 which means that the stack pointer is initialized to 0.
+Additional information:
+I examined the source code and I think that editing the function `avr_cpu_reset_hold` in `/target/avr/cpu.c` might fix this issue. This is my first time seeing QEMU source code, so I might be wrong, though.
+
+```c
+// in /target/avr/cpu.c line 70
+static void avr_cpu_reset_hold(Object *obj)
+{
+    // ...
+
+    env->rampD = 0;
+    env->rampX = 0;
+    env->rampY = 0;
+    env->rampZ = 0;
+    env->eind = 0;
+    env->sp = 0;    // <-- change this value in accordance with board type?
+
+    //...
+}
+```