armv8-bare-metal

• Purpose
  • It's a bare-metal study in QEMU (-M virt -cpu cortex-a57)
• How to run

  # export PATH inclueding your cross compile tool
  export PATH=$PATH:/home/ryanyao/work/buildroot-2017.11-rc1/output/host/bin
  make run
  

• GDB (Terminal 1/2 should be in the same directory.)

  Terminal 1:
  	qemu-system-aarch64 -machine virt -cpu cortex-a57 -kernel kernel.elf -nographic -S -s
  Terminal 2:
  	aarch64-linux-gnu-gdb kernel.elf --tui
  	target remote :1234
  

• Timer IRQ works. It assert Timer_Handler() every 1 sec.

  timer_test
  gic_v3_initialize()
  init_gicd()
  init_gicc()
  CurrentEL = 0x00000000 00000004
  RVBAR_EL1 = 0x00000000 00000000
  VBAR_EL1 = 0x00000000 40000000
  DAIF = 0x00000000 000003C0
  Disable the timer, CNTV_CTL_EL0 = 0x00000000 00000000
  System Frequency: CNTFRQ_EL0 = 0x00000000 03B9ACA0
  Current counter: CNTVCT_EL0 = 0x00000000 0001BA16
  Assert Timer IRQ after 1 sec: CNTV_CVAL_EL0 = 0x00000000 03BB66B6
  Enable the timer, CNTV_CTL_EL0 = 0x00000000 00000001
  Enable IRQ, DAIF = 0x00000000 00000340
  
  Exception Handler! (AARCH64_EXC_IRQ_SPX)
  IRQ found: 0x00000000 0000001B
  timer_handler:
  		Disable the timer, CNTV_CTL_EL0 = 0x00000000 00000000
  		System Frequency: CNTFRQ_EL0 = 0x00000000 03B9ACA0
  		Current counter: CNTVCT_EL0 = 0x00000000 03BD40D5
  		Assert Timer IRQ after 0x00000000 00000001 sec(s): CNTV_CVAL_EL0 = 0x00000000 0776ED75
  		Enable the timer, CNTV_CTL_EL0 = 0x00000000 00000001
  
  Exception Handler! (AARCH64_EXC_IRQ_SPX)
  IRQ found: 0x00000000 0000001B
  timer_handler:
  		Disable the timer, CNTV_CTL_EL0 = 0x00000000 00000000
  		System Frequency: CNTFRQ_EL0 = 0x00000000 03B9ACA0
  		Current counter: CNTVCT_EL0 = 0x00000000 0778E288
  		Assert Timer IRQ after 0x00000000 00000001 sec(s): CNTV_CVAL_EL0 = 0x00000000 0B328F28
  		Enable the timer, CNTV_CTL_EL0 = 0x00000000 00000001
  

Issues

• GDB can't step into main() if miss lable: main_label in boot.S (commit b72c6a8cc7033a4fed89b57f75826d201466179f)
• (Fixed, 2018/07/19) Timer IRQ doesn't work(commit b72c6a8cc7033a4fed89b57f75826d201466179f)
  • We can see CNTV_CTL_EL0[2]:ISTATUS changes, but irq_handler doesn't be called.
  • And we also didn't see any changes in ISR_EL1.
  • Solved in commit 2aaa0bff7516e84e01acd10d8de64189839d9d51.
• (Fixed, 2018/07/05) It should be some problems in vector_table_el1 in boot.S. If I set "b hang" in other vectors except lower_el_aarch64_irq, the uart outpt will be incorrect or system hang (commit b72c6a8cc7033a4fed89b57f75826d201466179f)
  • Root cause should be the stack memory is overlaid. Now, we set stack_top = 0x41000000 to avoid it. (commit c14d653fca24387b5996285f45f0fef2906cb2c9)

Reference

• Project
  • aarch64-bare-metal-qemu
  • raspberrypi
  • sample-tsk-sw
• QEMU
  • QEMU version 2.12.50 User Documentation
• Makefile
  • Makefile範例教學
  • GNU 的連結工具 (ld, nm, objdump, ar)
  • GCC Command-Line Options
  • LD Index
• ARM
  • Arm® Compiler armasm User Guide
  • Application Note Bare-metal Boot Code for ARMv8-A Processors Version 1.0
  • ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture profile Beta
  • ARM® Cortex®-A57 MPCore™ Processor Revision: r1p0 Technical Reference Manual
  • ARM® Cortex®-A Series Version: 1.0 Programmer’s Guide for ARMv8-A
  • ARM® Generic Interrupt Controller Architecture Specification GIC architecture version 3.0 and version 4.0