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Microsoft's Azure RTOS ThreadX for Renesas RXv3
Using the GNU Tools
1. Building the ThreadX run-time Library
Please see the Samples repository on GitHub for the Azure RTOS demonstrations
for the RXv3.
2. Demonstration System
Please see the Samples repository on GitHub for the Azure RTOS demonstrations
for the RXv3.
3. System Initialization
The system entry point using the GNU tools is at the label _PowerON_Reset.
The vector area is setup in the file tx_initialize_low_level.S. This file is also
responsible for setting up various system data structures, interrupt vectors, and
the periodic timer interrupt. This file is also an ideal place to add additional hardware
initialization code.
The ThreadX demonstration for the RXv3 utilizes CMT0 as a periodic timer interrupt
source. The CMT0 interrupt is typically setup for 10ms periodic interrupts and the
interrupt priority level is set to level 5 with the symbol CMT_RX_CFG_IPR in
r_cmt_rx_config.h of Renesas CMT timer module(r_cmt_rx). You may change any of the timer
parameters as needed. Increasing the timer interrupt frequency increases the overhead
of the timer handling code on the system.
In addition, _tx_initialize_low_level determines the first available address for use
by the application, which is supplied as the sole input parameter to your application
definition function, tx_application_define. The first available memory is determined
by the location of the '_end' label the is defined in the linker script.
'_end' should reference the first memory AFTER all other RAM
sections in your linker control file.
4. Context Switch, Register Usage and Stack Frames
The RXv3 port for ThreadX uses the first software interrupt, SWINT, i.e., interrupt #27,
to perform context switch with the interrupt priority level 1. This ISR is thus reserved
when using ThreadX and the SWINT should not be manipulated in any way by the application.
The port will setup the interrupt within _tx_initialize_low_level and the compiler will
automatically install the necessary interrupt vector. As such no additional initialization
is necessary by the application.
The following defines the saved context stack frame used by the ThreadX port. The
state of the CPU registers at the time of a context switch is saved on the running
thread's stack The top of the suspended thread's stack is pointed to by
tx_thread_stack_ptr in the associated thread control block TX_THREAD.
Offset Stack Frame without DFPU Register
0x00 ACC0
0x04 ACC1
0x08 R6
0x0C R7
0x10 R8
0x14 R9
0x18 R10
0x1C R11
0x20 R12
0x24 R13
0x28 FPSW
0x2C R14
0x30 R15
0x34 R3
0x38 R4
0x3C R5
0x40 R1
0x44 R2
0x48 PC - return address
0x4C PSW
Offset Stack Frame with DFPU Register
0x00 DPSW
0x04 DCMR
0x08 DECNT
0x0C DEPC
0x10 DR0
0x14 DR1
0x18 DR2
0x1C DR3
0x20 DR4
0x24 DR5
0x28 DR6
0x2C DR7
0x30 DR8
0x34 DR9
0x38 DR10
0x3C DR11
0x40 DR12
0x44 DR13
0x48 DR14
0x4C DR15
0x50 ACC0
0x54 ACC1
0x58 R6
0x5C R7
0x60 R8
0x64 R9
0x68 R10
0x6C R11
0x70 R12
0x74 R13
0x78 FPSW
0x7C R14
0x80 R15
0x84 R3
0x88 R4
0x8C R5
0x90 R1
0x94 R2
0x98 PC - return address
0x9C PSW
Note: By default GNURX does not save the state of the accumulator registers ACC0 and ACC1
when entering an ISR. This means that if the ISR uses any of the DSP instructions the
content of those registers could be corrupted. Saving and restoring of the accumulators
can be enabled by adding the -msave-acc-in-interrupts command line option.
5. Double Precision FPU Instructions Support
The RXv3 architecture supports an optional set of double precision instructions which
makes use of a new set of registers that must be saved and restored during context
switches. This feature can be accessed by adding the -mdfpu -m64bit-doubles compiler switches.
To reduce the overhead of saving and restoring the FPU registers for all threads
the RXv3 port allows each thread to enable and disable saving and restoring the DFPU
registers. By default the feature is disabled for new threads. To enable the feature
tx_thread_fpu_enable() must be called within the context of every thread that will
perform FPU operation. The saving and restoring of DFPU registers can be disabled
again by calling tx_thread_fpu_disable(). This can be useful if a thread only makes
occasional use of the FPU.
6. Improving Performance
The distribution version of ThreadX is built without any compiler optimizations. This
makes it easy to debug because you can trace or set breakpoints inside of ThreadX itself.
Of course, this costs some performance. To make ThreadX run faster, you can change the
ThreadX Library project to disable debug information and enable the desired optimizations.
In addition, you can eliminate the ThreadX basic API error checking by compiling your
application code with the symbol TX_DISABLE_ERROR_CHECKING defined before tx_api.h
is included.
7. Timer Processing
Timer processing is performed by calling __tx_timer_interrupt(). This should usually be done
from within the callback of a periodic timer with a period of 100Hz. In the sample projects,
a Renesas Fit CMT periodic timer module (r_cmt_rx) is used as the timer source.
8. Interrupt Handling
Interrupt handling is unaffected by the ThreadX port as such user interrupts can be
written according to the toolchain's documentation. It is recommended not to use interrupt
priority 1 as this is the priority of the context switch interrupt. However using interrupt
priority 1 won't cause any negative side effects but doing so may slightly reduce
performance. Please refer to the toolchain documentation for additional details on how to
define interrupt service routines.
9. Execution Profiling
The RX port adds support for the Execution Profiling Kit (EPK). The EPK consists
of the files tx_execution_profile.c and tx_execution_profile.h. See the documentation
of the EPK for generic usage details.
To add the EPK to your RXv3 release make the following modifications:
* Enable the following define for both the Threadx library and the application
TX_EXECUTION_PROFILE_ENABLE
* Setup CMT1 as a free running 16 bit timer.
* In tx_execution_profile.h, change following around line 52:
#ifdef TX_EXECUTION_64BIT_TIME
typedef unsigned long long EXECUTION_TIME;
#define TX_EXECUTION_MAX_TIME_SOURCE 0xFFFFFFFFFFFFFFFF
#else
typedef unsigned long EXECUTION_TIME;
#define TX_EXECUTION_MAX_TIME_SOURCE 0xFFFF
#endif
/* Define basic constants for the execution profile kit. */
#define TX_EXECUTION_TIME_SOURCE (EXECUTION_TIME) *((USHORT *) 0x8800A)
Rebuild the Threadx library and the application.
Refer to the EPK documentation how to interpret the results.
10. Revision History
For generic code revision information, please refer to the readme_threadx_generic.txt
file, which is included in your distribution. The following details the revision
information associated with this specific port of ThreadX:
04-25-2022 Release 6.1.11 changes:
tx_thread_schedule.s Added low power support
01-31-2022 Release 6.1.10 changes:
tx_port.h Added missing interrupt control defines
tx_timer_interrupt.s Added missing thread preemption logic
10-15-2021 Release 6.1.9 changes:
tx_port.h Added FPU support
tx_thread_context_restore.s Added FPU support
tx_thread_schedule.s Added FPU support
tx_thread_system_return.s Added FPU support
06-02-2021 Initial ThreadX release for the RXv3 using GNURX tools, version 6.1.7
Copyright(c) 1996-2022 Microsoft Corporation
https://azure.com/rtos
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