Intel IXP400 Digital Signal Processing (DSP) Software: Priority Setting for 10 ms Real Time Task Application Note November 2005 Document Number: 310033, Revision: 001 November 2005
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Contents 1.0 Introduction...5 1.1 Scope...5 1.2 Related Documents...5 1.3 Acronyms...5 2.0 Priority Setting for 10 ms Real Time Task in Linux*...5 3.0 Priority Setting for 10 ms Real Time Task in VxWorks*...8 4.0 Conclusion...8 Figures 1 Intel IXP400 DSP Software Message, Data, and Tasks...6 Revision History Date Revision Description November 2005 001 Initial release of document. Application Note Priority Setting for 10 ms Real Time Task November 2005 Document Number: 310033, Revision: 001 3
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1.0 Introduction During initialization of Intel IXP400 DSP Software, real-time tasks are created. The 10- millisecond (ms) Real Time Task is created to process data flows for G.711 and G.729 coders, and handles all other non-coder voice processing, such as echo cancellation and tone detection. If 10 ms Real Time Task cannot finish its processing before the next task period, voice quality is degraded. Setting the priority for the Task is one of the ways to ensure that it has higher priority when scheduled for execution. 1.1 Scope This application note is intended to explain how to set the priority for 10 ms Real Time Task of Intel IXP400 DSP Software v2.6.2. Further information can be found in the documents shown in Section 1.2. 1.2 Related Documents Document Intel IXP400 Digital Signal Processing (DSP) Software Version 2.6.2 API Reference Manual Intel IXP400 Digital Signal Processing (DSP) Software Version 2.6.2 Programmer s Guide Intel IXP400 Digital Signal Processing (DSP) Software Version 2.6.2 Release Notes Document Number 273811 252725 N/A 1.3 Acronyms Acronym API DSP HSS ISR NPE PCM Description Application Programming Interface Digital Signal Processing High Speed Serial Interrupt Service Routine Network Processing Engine Pulse Code Modulation 2.0 Priority Setting for 10 ms Real Time Task in Linux* The DSP software creates 10 ms Real Time Task to generate or consume audio data at 10 ms intervals essentially synchronized with PCM data from HSS NPE or external PCM device. See Figure 1. Application Note Priority Setting for 10 ms Real Time Task November 2005 Document Number: 310033, Revision: 001 5
Figure 1. Intel IXP400 DSP Software Message, Data, and Tasks Intel IXP400 DSP Software Module Intel IXP400 DSP Software Client Application Control Task Control Messages Interrupt Ethernet NPE IP Packets SLIC Interface HSS NPE or External PCM device 8-bit PCM Data Interrupt HSS Buffer 16-bit PCM Data Scheduler Real-Time Task Job Management Egress Encoded Packets Jitter Buffer IP Stack IP ISR IP Task Ingress Encoded Packets B4159-01 The HSS NPE or External PCM device generates an interrupt every 10 ms. The ISR services HSS buffers (copy data to/from the buffers), update the job queue and update other parameters such as time stamp. The Linux* Kernel Scheduler uses the job queue for scheduling any pending task to run. It is possible that the 10 ms Real Time Task is delayed under certain conditions. This condition will happen when there are multiple tasks having higher priority than the 10 ms Real Time Task or the current active task, having the same or higher priority than the 10 ms Real Time Task execute for more than 10 ms. This will affect the performance of the DSP software and affect the overall voice quality. Hence, it is important to ensure that 10 ms Real Time Task has the highest priority. Other tasks should have a lower priority and should not execute for a period longer than 10 ms. To change the static priority of 10 ms Real Time Task: For IXP400 Software Release Version 1.3, modify ixp425_xscale_sw/src/linux/vx.c For IXP400 Software Release Version 1.4, modify ixp400_xscale_sw/src/linux/vx.c November 2005 Priority Setting for 10 ms Real Time Task Application Note 6 Document Number: 310033, Revision: 001
#include <linux/slab.h> #include <asm/uaccess.h> #include vx.h int taskspawn(char *name, int priority, int options, int stack_sz, FUNCPTR entry_pt, int arg1, int arg2, int arg3, int arg4, int arg5, int arg6, int arg7, int arg8, int arg9, int arg10) { pid_t pid; int retval = -2; struct sched_param prm2; mm_segment_t fs; long policy; down(&data_mutex); if (pid < 0) { up(&data_mutex); return ERROR; } /* To set the priority if the task spawned is 10ms Real Time Task */ if (strncmp(task_data.name, DspRtTsk10, sizeof(task_data.name)) == 0) { fs = get_fs(); set_fs(get_ds()); } } return (int)pid; /*Choose a static priority within the valid range (1 to 99)*/ prm2.sched_priority= 10; /* Please choose either SCHED_RR or SCHED_FIFO when calling setscheduler*/ retval = setscheduler (pid, SCHED_RR, &prm2); set_fs(fs); if (retval ==0) { printk ( Successfully set 10ms Real Time Task Priority );} else {printk ( Error in setting 10ms Real Time Task Priority );} After modification, ixp400.o needs to be recompiled. Please refer to the Intel IXP400 DSP Software v2.6.2 Release Notes for steps on how to compile ixp400.o. Application Note Priority Setting for 10 ms Real Time Task November 2005 Document Number: 310033, Revision: 001 7
3.0 Priority Setting for 10 ms Real Time Task in VxWorks* 10 ms Real Time Task in VxWorks* can be set by providing appropriate base priority setting during initialization stage of calling xdspsysinit() function. Please see the Intel IXP400 Digital Signal Processing (DSP) Software Version 2.6.2 API Reference Manual for more details. 4.0 Conclusion The 10 ms Real Time Task priority for DSP software release 2.6.2 can be set accordingly in Linux by modifying vx.c file, and in VxWorks by providing appropriate base priority during initialization. November 2005 Priority Setting for 10 ms Real Time Task Application Note 8 Document Number: 310033, Revision: 001