From fadac1567aed13591a7ccf463b5887b083d2299f Mon Sep 17 00:00:00 2001
From: Arturs Artamonovs <dos21h@gmail.com>
Date: Thu, 19 Jun 2025 22:14:16 +0100
Subject: pre published notes on raspi5 baremetal debuging

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 md/writeup/raspberry5_baremetal_helloworld.md | 229 ++++++++++++++++++++++++++
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 create mode 100644 md/writeup/raspberry5_baremetal_helloworld.md

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+title: Raspberry 5 baremetal Hello World example
+keywords:raspi5,asm,c,kernel,arm64
+
+# Raspberry 5 baremetal Hello World example
+
+## Intro
+
+Here is base example that will allow to print out message to serial console,
+and debug application. This example is picked up from variouse resources to
+make easy start into baremetal programming for raspi5, similar route is for
+all other models. All commands are tested from raspi4, adjust sources 
+for your system. 
+
+## Source code
+
+
+### boot.S
+
+```
+.section ".text.boot"
+
+.global _start
+
+_start:
+    // read cpu id, stop slave cores
+    mrs     x1, mpidr_el1
+    and     x1, x1, #3
+    cbz     x1, 2f
+    // cpu id > 0, stop
+1:  wfe
+    b       1b
+2:  // cpu id == 0
+
+    // set top of stack just before our code (stack grows to a lower address per AAPCS64)
+    ldr     x1, =_start
+    mov     sp, x1
+
+    // clear bss
+    ldr     x1, =__bss_start
+    ldr     w2, =__bss_size
+3:  cbz     w2, 4f
+    str     xzr, [x1], #8
+    sub     w2, w2, #1
+    cbnz    w2, 3b
+
+    // jump to C code, should not return
+4:  bl      main
+    // for failsafe, halt this core too
+    b       1b
+
+```
+
+### kernel.c
+
+```c
+void main()
+{
+	while (1) {
+
+	}
+}
+```
+
+### Makefile
+```Makefile
+TOOLCHAIN=aarch64-linux-gnu-
+AS = ${TOOLCHAIN}as
+LD = ${TOOLCHAIN}ld
+SRCS = $(wildcard *.c)
+OBJS = $(SRCS:.c=.o)
+CFLAGS = -Wall -O2 -ffreestanding
+CC=$(TOOLCHAIN)gcc
+
+all: clean kernel8.img
+
+boot.o: boot.S
+	${CC} ${CFLAGS} -c boot.S -o boot.o 
+
+%.o: %.c
+	${CC} ${CFLAGS} -c $< -o $@
+
+kernel8.img: boot.o ${OBJS}
+	${LD} boot.o ${OBJS} -T linker.ld -o kernel8.elf
+	${TOOLCHAIN}objcopy -O binary kernel8.elf kernel8.img
+
+clean:
+	rm -rf *.o *.img *.elf
+```
+
+### config.txt
+```
+enable_jtag_gpio=1
+```
+
+### Compile source code
+```sh
+make
+```
+
+### Prepare for a boot
+
+
+
+```sh
+cp
+```
+
+
+
+## Debugging with OpenOCD+GDB
+
+The default openocd doesn't configration for raspi5.
+
+### OpenOCD config for bcm2712.cfg
+
+If OpenOCD doesn't have the raspi5 config by default here is one 
+that suppose to work. Copy it for example in default openocd script location in:
+
+```
+/usr/share/openocd/scripts/target/
+```
+
+
+```tcl
+# bcm2712.cfg
+# SPDX-License-Identifier: GPL-2.0-or-later
+# OpenOCD target config file
+# This file is based on target/bcm2711.cfg
+# I have checked that it works with Open On-Chip Debugger 0.12.0 
+# using the Raspberry Pi Debug-Probe interface
+
+transport select swd
+adapter speed 1000
+
+if { [info exists CHIPNAME] } {
+    set  _CHIPNAME $CHIPNAME
+} else {
+    set  _CHIPNAME bcm2712
+}
+
+if { [info exists CHIPCORES] } {
+    set _cores $CHIPCORES
+} else {
+    set _cores 4
+}
+
+if { [info exists USE_SMP] } {
+    set _USE_SMP $USE_SMP
+} else {
+    set _USE_SMP 0
+}
+
+if { [info exists DAP_TAPID] } {
+    set _DAP_TAPID $DAP_TAPID
+} else {
+    set _DAP_TAPID 0x2ba00477
+}
+
+# swj_newdap $_CHIPNAME cpu -irlen 4 -ircapture 0x1 -irmask 0xf -expected-id $_DAP_TAPID
+swd newdap $_CHIPNAME cpu -expected-id $_DAP_TAPID
+dap create $_CHIPNAME.dap -chain-position $_CHIPNAME.cpu
+
+# MEM-AP for direct access
+target create $_CHIPNAME.ap mem_ap -dap $_CHIPNAME.dap -ap-num 0
+
+# these addresses are obtained from the ROM table via 'dap info 0' command
+set _DBGBASE {0x80010000 0x80110000 0x80210000 0x80310000}
+set _CTIBASE {0x80020000 0x80120000 0x80220000 0x80320000}
+
+set _smp_command "target smp"
+
+for { set _core 0 } { $_core < $_cores } { incr _core } {
+    set _CTINAME $_CHIPNAME.cti$_core
+    set _TARGETNAME $_CHIPNAME.cpu$_core
+
+    cti create $_CTINAME -dap $_CHIPNAME.dap -ap-num 0 -baseaddr [lindex $_CTIBASE $_core]
+    target create $_TARGETNAME aarch64 -dap $_CHIPNAME.dap -ap-num 0 -dbgbase [lindex $_DBGBASE $_core] -cti $_CTINAME
+
+    set _smp_command "$_smp_command $_TARGETNAME"
+}
+
+if {$_USE_SMP} {
+    eval $_smp_command
+}
+
+# default target is cpu0
+targets $_CHIPNAME.cpu0
+```
+
+Connecting pico probe and doint step by step analysis of basic loop
+
+### Running OpenOCD 
+
+Start openocd server
+
+```
+openocd -f interface/cmsis-dap.cfg -f target/bcm2712.cfg
+```
+
+Connect with gdb
+
+```
+gdb
+```
+
+and run inside gdb shell
+
+```
+tar ext :3333
+```
+
+
+## Links
+
+
+https://www.raspberrypi.com/documentation/computers/config_txt.html
+https://wiki.osdev.org/Raspberry_Pi_Bare_Bones
+
+https://www.rpi4os.com/part1-bootstrapping/
+
+https://www.valvers.com/open-software/raspberry-pi/bare-metal-programming-in-c-part-1/
+
+https://www.raspberrypi.com/documentation/microcontrollers/debug-probe.html
+
+https://macoy.me/blog/programming/RaspberryPi5Debugging
+https://gist.github.com/tnishinaga/219122a5f1e3973668ee78c0fb1c7bf9
+https://forums.raspberrypi.com/viewtopic.php?p=2172522#p2172522
+
+https://github.com/DSERIOUSGUY/HobOS
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