Tools for inspecting ARM Cortex-M registers within GDB
Currently supported:
- SCB - System Control Block
- SysTick
- NVIC - Nested Vectored Interrupt Controller
pip install arm-gdb
Start GDB and run
python import arm_gdb
Or add that line to ~/.gdbinit
Use help arm command, or individual subcommands, i.e. help arm scb
(gdb) help arm
Tools for debugging ARM Cortex-M - series CPUs
List of arm subcommands:
arm fpu -- Dump of ARM Cortex-M FPU - SCB registers for the FP extension
arm inspect -- Dump register values from device peripheral
arm list -- List peripherals and registers from device
arm loaddb -- Load an SVD file from resitry
arm loadfile -- Load an SVD file from file
arm nvic -- Print current status of NVIC
arm scb -- Dump of ARM Cortex-M SCB - System Control Block
arm systick -- Dump of ARM Cortex-M SysTick block
Type "help arm" followed by arm subcommand name for full documentation.
Type "apropos word" to search for commands related to "word".
Type "apropos -v word" for full documentation of commands related to "word".
Command name abbreviations are allowed if unambiguous.
(gdb) help arm scb
Dump of ARM Cortex-M SCB - System Control Block
Usage: arm scb [/habf]
Modifier /h provides descriptions of names where available
Modifier /a Print all fields, including default values
Modifier /b prints bitmasks in binary instead of hex
Modifier /f force printing fields from all Cortex-M models
Dump of ARM System Control Block, with bitmask descriptions
(gdb) arm scb /h
SCB for model M4
SCB registers:
CPUID = 410fc241 // CPUID Base Register
Implementer 41...... - ARM // Implementer code assigned by Arm
Architecture ...f.... - f // constant - 1111
PartNo ....c24. - Cortex-M4
Revision .......1 - 1
ICSR = 00000000 // Interrupt Control and State Register
VTOR = 00000000 // Vector Table Offset Register
AIRCR = fa050000 // Application Interrupt and Reset Control Register
ENDIANNESS ....0... - Little Endian
SCR = 00000000 // System Control Register
CCR = 00000200 // Configuration and Control Register
SHPR1 = 00000000 // System Handler Priority Register 1
SHPR2 = 80000000 // System Handler Priority Register 2
PRI_11 - SVCall 80...... - 80 // Priority of system handler 11, SVCall.
SHPR3 = 00e00000 // System Handler Priority Register 3
PRI_14 - PendSV ..e0.... - e0 // Priority of system handler 14, PendSV.
SHCSR = 00070000 // System Handler Control and State Register
USGFAULTENA ...4.... - 1 // Indicates if UsageFault is enabled.
BUSFAULTENA ...2.... - 1 // Indicates if BusFault is enabled.
MEMFAULTENA ...1.... - 1 // Indicates if MemFault is enabled.
CFSR = 00000000 // Configurable Fault Status Register
MMFSR ......00 - 00 // MemManage Fault Status Register
BFSR ....00.. - 00 // BusFault Status Register
UFSR 0000.... - 0000 // UsageFault Status Register
HFSR = 00000000 // HardFault Status Register
DFSR = 00000001 // Debug Fault Status Register
HALTED .......1 - Halt request debug event // Indicates a debug event generated by either C_HALT, C_STEP or DEMCR.MON_STEP
MMFAR = e000edf8 // MemManage Fault Address Register
BFAR = e000edf8 // BusFault Address Register
AFSR = 00000000 // Auxiliary Fault Status Register
CPACR = 00f00000 // Coprocessor Access Control Register
AUX registers:
ICTR = 00000001 // Interrupt Controller Type Register
INTLINESNUM .......1 - 64 vectors // The total number of interrupt lines supported, as 32*(1+N)
ACTLR - M4 = 00000000 // Auxiliary Control Register - Cortex M4
(gdb) help arm systick
Dump of ARM Cortex-M SysTick block
Usage: arm systick [/hab]
Modifier /h provides descriptions of names where available
Modifier /a Print all fields, including default values
Modifier /b prints bitmasks in binary instead of hex
Dump of ARM SysTick
(gdb) arm systick
SYST_CSR = 00000004
CLKSOURCE .......4 - 1
SYST_RVR = 00000000
SYST_CVR = 00000000
SYST_CALIB = c0000000
SKEW 4....... - 1
NOREF 8....... - 1
... or with descriptions
(gdb) arm systick /h
SYST_CSR = 00000004 // SysTick Control and Status Register
CLKSOURCE .......4 - 1
SYST_RVR = 00000000 // SysTick Reload Value Register
SYST_CVR = 00000000 // SysTick Current Value Register
SYST_CALIB = c0000000 // SysTick Calibration Value Register
SKEW 4....... - 1
NOREF 8....... - 1
... or with bitmasks in binary
(gdb) arm systick /b
SYST_CSR = 00000000000000000000000000000100
CLKSOURCE .............................1.. - 1
SYST_RVR = 00000000000000000000000000000000
SYST_CVR = 00000000000000000000000000000000
SYST_CALIB = 11000000000000000000000000000000
SKEW .1.............................. - 1
NOREF 1............................... - 1
Print out all fields, even those with default values:
(gdb) arm systick /ab
SYST_CSR = 00000000000000000000000000000100
ENABLE ...............................0 - 0
TICKINT ..............................0. - 0
CLKSOURCE .............................1.. - 1
COUNTFLAG ...............0................ - 0
SYST_RVR = 00000000000000000000000000000000
RELOAD ........000000000000000000000000 - 000000
SYST_CVR = 00000000000000000000000000000000
CURRENT ........000000000000000000000000 - 000000
SYST_CALIB = 11000000000000000000000000000000
TENMS .......0000000000000000000000000 - 0000000
SKEW .1.............................. - 1
NOREF 1............................... - 1
(gdb) help arm fpu
Dump of ARM Cortex-M FPU - SCB registers for the FP extension
Usage: arm fpu [/hab]
Modifier /h provides descriptions of names where available
Modifier /a Print all fields, including default values
Modifier /b prints bitmasks in binary instead of hex
(gdb) arm fpu/ab
SCB FP registers:
FPCCR = 11000000000000000000000000000000
ASPEN 1............................... - 1
LSPEN .1.............................. - 1
MONRDY .......................0........ - 0
BFRDY .........................0...... - 0
MMRDY ..........................0..... - 0
HFRDY ...........................0.... - 0
THREAD ............................0... - 0
USER ..............................0. - 0
LSPACT ...............................0 - 0
FPCAR = 00000000000000000000000000000000
FPCAR ..0000000000000000000000000000.. - 0000000
FPDSCR = 00000000000000000000000000000000
AHP .....0.......................... - 0
DN ......0......................... - 0
FZ .......0........................ - 0
RMode ........00...................... - 0
MVFR0 = 00010000000100010000000000100001
FP rounding modes 0001............................ - All rounding modes supported.
Short vectors ....0000........................ - Not supported
Square root ........0001.................... - Supported
Divide ............0001................ - Supported
FP exception trapping ................0000............ - Not supported
Double-precision ....................0000........ - Not supported
Single-precision ........................0010.... - Supported.
A_SIMD registers ............................0001 - Supported, 16 x 64-bit registers.
MVFR1 = 00010001000000000000000000010001
FP fused MAC 0001............................ - Supported
FP HPFP ....0001........................ - Supported half-single
D_NaN mode ........................0001.... - Supported
FtZ mode ............................0001 - Hardware supports full denormalized number arithmetic.
MVFR2 = 00000000000000000000000000000000
VFP_Misc ........................0000.... - No support for miscellaneous features.
Dump of NVIC list, listing all enabled interrupt handlers, in a redirected interrupt vector
(gdb) help arm nvic
Print current status of NVIC
Usage: arm nvic [/a] [<ISR vector address>]
Modifier /a lists all interrupt vectors, not only enabled
<ISR vector address> - optional. Specifies base address of ISR vector.
If not specified, it will be resolved via SCB->VTOR,
which is valid in most cases.
Examples:
arm nvic /a - list all ISRs from -15 to to maximum
arm nvic &__isr_vector - Custom ISR vector, useful when proxying
interrupts via another system, like the
softdevice on nRF52
Default, it checks for functions in the active interrupt vector given VTOR register. But in for example nRF52840 using their SoftDevice, the interrupts are forwarded in software to the application for SoftDevice to override.
(gdb) arm nvic &__isr_vector
IRQn Prio Handler
-15 0 en 0002a749 Reset -
-14 0 en 0002a771 NMI -
-13 0 en 0002bc55 HardFault HardFault_Handler
-12 0 en 0002bc5d MemManage
-11 0 en 0002bc59 BusFault
-10 0 en 0002bc61 UsageFault
-5 80 en 00027201 SVC SVC_Handler
-2 e0 en 00027231 PendSV PendSV_Handler
0 80 en 00027715 POWER_CLOCK_IRQHandler
2 40 en 0002c409 UARTE0_UART0_IRQHandler
11 0 en 0002a783 -
17 c0 en pend 0002bd4d RTC1_IRQHandler
21 40 en 0002bd55 SWI1_EGU1_IRQHandler
22 c0 en 000279e9 SWI2_EGU2_IRQHandler
23 a0 en 0002c035 SWI3_EGU3_IRQHandler
25 80 en 0002a783 -
32 20 en 0002a783 -
(gdb) help arm inspect
Dump register values from device peripheral
Usage: arm inspect [/hab] <device> <peripheral>
Modifier /h provides descriptions of names where available
Modifier /a Print all fields, including default values
Modifier /b prints bitmasks in binary instead of hex
<device> - Name of loaded device. See `help arm loadfile`
<peripheral> - Name of peripheral
Exmaple: arm inspect nrf52840 UARTE0
(gdb) help arm loaddb
Load an SVD file from resitry
Usage: arm loaddb <device> <vendor> <filename>
<device> - Name to refer to the device in commands like `arm inspect`
<vendor> - Device vendor
<filename> - SVD file within registry
Load file from cmsis-svd package registry. Many common devices are available. If
not available, you can load a custom svd file using `arm loadfile`
This command can preferrably be added to .gdbinit for easy access of devices
(gdb) help arm loadfile
Load an SVD file from file
Usage: arm loadfile <device> <filename>
<device> - Name to refer to the device in commands like `arm inspect`
<filename> - SVD file to load
This command can preferrably be added to .gdbinit for easy access of devices
(gdb) help arm list
List peripherals and registers from device
Usage: arm list
Lists loaded devices
Usage: arm list <device>
List peripherals from a device
Usage: arm list <device> <peripheral>
List registers from a peripheral
Examples:
arm list
arm list nrf52840
arm list nrf52840 UARTE0
To use an SVD file from cmsis-svd package database, use:
(gdb) arm loaddb nrf Nordic nrf52.svd
This loads in the device description under a local name, in this case nrf for
faster access in upcoming commands
It is also possible to load custom svd files, in this case an stm32f7x7:
(gdb) arm loadfile stm32f7x7 /path/to/my/stm32f7x7.svd
To list peripherals in the loaded module, use:
(gdb) arm list nrf
FICR @ 0x10000000
UICR @ 0x10001000
BPROT @ 0x40000000
POWER @ 0x40000000
...
It is possible to inspect the values of the registers on the target
(gdb) arm inspect nrf52840 NVMC
NVMC.READY = 00000001
READY .......1 - Ready
NVMC.READYNEXT = 00000001
READYNEXT .......1 - Ready
NVMC.CONFIG = 00000000
WEN .......0 - Ren
NVMC.ERASEPAGE = 00000000
NVMC.ERASEPCR1 = 00000000
NVMC.ERASEALL = 00000000
ERASEALL .......0 - NoOperation
NVMC.ERASEPCR0 = 00000000
NVMC.ERASEUICR = 00000000
ERASEUICR .......0 - NoOperation
NVMC.ERASEPAGEPARTIAL = 00000000
NVMC.ERASEPAGEPARTIALCFG = 0000000a
DURATION ......0a - 0a
NVMC.ICACHECNF = 00000001
CACHEEN .......1 - Enabled
CACHEPROFEN .....0.. - Disabled
NVMC.IHIT = 00000000
NVMC.IMISS = 00000000