Research on Auxiliary Clock of AT91RM9200 Platform

introduction

In VxWorks, the implementation of the timer mechanism is based on the clock. Different timing mechanisms can be selected according to different requirements, such as taskDelay(), WatchDog, and auxiliary clock . The first two timings are based on the system clock.

taskDelay() is the simplest delay method. Its unit is tick, so its delay accuracy is not high, but it is sufficient for systems with delays of more than 10 ms. Using taskDelay(), the called task can be transferred from the ready state to the sleep state, but it cannot be used in interrupt service routines. In addition, by calling taskDelay(0), the CPU can be handed over to other tasks of the same priority in the system.

The watchdog timer is maintained as part of the system clock interrupt service routine. Therefore, the functions associated with the watchdog timer run at the system clock interrupt level, and the delay unit is tick. If the application requires multiple watchdog functions, wdCreate() can be used to generate independent watchdog IDs for each requirement, because for a given watchdog ID, only the most recent wdStart() is valid. With the watchdog timer, the calling task will not be blocked because the wdStart() call returns immediately. But it is generally only suitable for systems with a delay of more than 10ms.

If a higher precision timing (such as 1 ms) is required in practice, then the use of auxiliary clock is a very desirable method. Generally, auxiliary clock is not configured in the BSP of VxWorks system. This article introduces the configuration and use of auxiliary clock in detail so that it can be used flexibly in practice.

1 AT91RM9200 Industrial Platform Clock and Timer

The research in this paper is based on the AT91RM9200 industrial platform, so it is necessary to first introduce the clock and timer under this platform.

AT91RM9200 provides two 3-channel 16-bit timer/counters (TC). Although the three channels are independent, they operate in the same way. Each channel is user-configurable, including three external clock inputs (XC0, XCl or XC2), five internal clock inputs (TIMER_CLOCK1, TIMER_CLOCK2, TIMER CLOCK3, TIMER_CL0CK4, TIMER_CLOCK5), and two multi-function input/output signals that can be configured by the user. In addition, each channel can work in two different modes, namely capture mode and waveform mode. Among them, the capture mode provides signal measurement, and the waveform mode is used to generate waveforms, which can be programmed by the WAVE bit of the TC channel mode register. The block diagram of the timer/counter is shown in Figure 1.

Among them, if the channel signal is selected, XCO, XCl, and XC2 represent three external clock inputs; TIOA and TIOB represent two multi-function input/output signals acting on each channel; INT represents interrupt signal output; and SYNC represents synchronous input signal. If the block signal is selected, TCLKO, TCLKl, and TCLK2 represent three external clock inputs; TIOAO~TIOA2 represent the TIOA signals of channels 0 to 2, and TIOB0~TIOB2 represent the TI0B signals of channels 0 to 2.

Among them, the five internal clock inputs are related to the main clock (MCK), the slow clock (SLCK) and the clock after the main clock is divided, as listed in Table 1.

2 Configuration of auxiliary clocks in VxWorks

If you want to use the auxiliary clock in the VxWorks operating system, you must go through certain configurations before you can use it. First, you need to define it in the VxWorks component or config.h:

#define INCLUDE_AUX_CLK

If it is not defined, the auxiliary clock cannot be used. In addition, the auxiliary clock needs to be initialized in the sysHwlnit2 function of sysLib.C, that is, the interrupt connection configuration:

(void)intConnect(AUX_TIMER_INT_VEC, sysAuxClkInt, O)

The difference between the auxiliary clock and the system clock is that the auxiliary clock must be provided by the user in the ISR, but calling tickAnnounce() in the ISR is not allowed, otherwise it will disrupt the system clock mechanism.

The configuration of the auxiliary clock can be modified according to the function template in installDir/target/drv/timer/templateTimer. C. The driver used in this article is At91Rm9200timer. c, and the header file is At91Rm9200timer. h. The modifications made in this file need to be made according to the specific chip it depends on, that is, it is necessary to refer to the AT91RM9200 chip data sheet.

The functions related to the auxiliary clock are: sysAuxClkInt(), sysAux-ClkConnect(), sysAuxClkDisable(), sysAuxClkEnable(), sysAuxClkRateGet() and sysAuxClkRateSet(). Among them, sysAuxClkRateGet() can be regarded as a group with sysAuxClkRateSet(). sysAuxClkRateGet() reads the clock frequency set by the sysAuxClkRateSet() function, and the clock frequency setting in the sysAuxClkRateSet() function is limited by AUX_CLK_RATE_MIN and AUX_CLK_RATE_MAX. This maximum and minimum value needs to be defined, and the definition location may be different. Some are placed in eonfig.h, and some are placed in bsp.h. The maximum and minimum values ​​in this article are defined in Inte-grator.h. The next two functions that need to be discussed are sysAux-ClkInt() and sysAuxClkEnable().

The sysAuxClkInt() function calls the user-defined interrupt processing function, and the interrupt processing function called by the user is connected by the sysAuxClkConnect() function. Before calling the interrupt processing function, you must first clear the interrupt operation, such as:

AMBA_TIMER_READ(AMBA_TIMER_T2SR(AMBA_TIMER_BASE), temp);

Otherwise, the CPU will be stuck in interruption and cannot do anything else.