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AN1216 APPLICATION NOTE
Implementing a Periodic Alarm with TIMEKEEPER
The TIMEKEEPER M48T59 and M48T59Y, from STMicroelectronics, each provide an 8K x 8 bit non volatile static RAM, and an integrated real time clock. Each also provides an alarm which can be set either for a given time and day, or to repeat at a certain day in every month, or at a certain hour in every day, or at a certain minute of every hour, or at a certain second of every minute. With this functionality already provided in the hardware, the software to implement an alarm of any given period is greatly simplified, as described in this document. Although specifically tailored for the M48T59 (or M48T59Y) device, the ideas can be adapted easily to use any of ST's other TIMEKEEPER devices that have the alarm feature. Some modifications in the MCU memory mapping (the TIMEKEEPER address space) and in the MCU register mapping (such as the pointer to register address) would need to be made. Table 1. Typical TIMEKEEPER (M48T59) Register Map
Data Address D7 1FFFh 1FFEh 1FFDh 1FFCh 1FFBh 1FFAh 1FF9h 1FF8h 1FF7h 1FF6h 1FF5h 1FF4h 1FF3h 1FF2h 1FF1h 1FF0h WDF 0 0 0 0 0 ST W WDS AFE RPT4 RPT3 RPT2 RPT1 R BMB4 0 0 0 D6 D5 D4 D3 D2 Year 10M 10 Date 0 0 0 Month Date Day Hours 10 Minutes Seconds Calibration BMB2 0 BMB1 0 BMB0 0 RB1 0 RB0 0 D1 D0 Year Month Date Day Hour Minute Second Control Watch Interrupt A Date A Hour A Minute A Second unused Z Z Flags 01-31 00-23 00-59 00-59 10 Years 0 0 FT 0 0 Function Range (in BCD Format) 00-99 01-12 01-31 01-7 00-23 00-59 00-59
10 Hours 10 Minutes 10 Seconds S BMB3 ABE
AI 10 Date AI 10 Hour Alarm 10 Minutes
Alarm Date Alarm Hour Alarm Minutes Alarm Seconds unused
Alarm 10 Seconds unused AF 0 BL Z
Z
February 2000
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TIMEKEEPER CONFIGURATION The TIMEKEEPER register mapping is shown in Table 1. This is divided in two parts: the clock registers and the alarm registers. Clock Registers The clock registers can be configured in the C language computer program as follows:
*TIMEKEEPER_CAL |= 0x80 *TIMEKEEPER_SEC= 00 //user clock setting : seconds parameter *TIMEKEEPER_MIN= 00 //user clock setting : minutes parameter *TIMEKEEPER_HOUR= 00 //user clock setting : hours parameter *TIMEKEEPER_CAL&= 0x7F
The process for starting the clock and making the calibration adjustments are described in the M48T59 data sheet, and in application notes AN925 and AN934. Alarm Registers It is necessary to set the Write bit, W, at the top of the control register (at address offset 1FF8h) before proceeding to any clock modification. Modifications to the alarm registers, though, can be made at any time, with no prior changes to the control register being necessary. The program listing, at the end of this document, contains statements to perform the following functions: 1. The Stop bit (ST, bit 7 of the register at offset 1FF9h) has to be reset to start the TIMEKEEPER oscillator
*TIMEKEEPER_SEC &= 0x7F; // reset bit D7 using a mask 0x7F
2. The Alarm Flag Enable (AFE) bit (bit 7 of the register at offset 1FF6h) is set, thereby allowing the IRQ pin (pin 26) to output the interrupt signal (active low).
*TKPER_AL_IT |= 0x80; // set bit D7 using a mask 0x80
3. The flag register (at offset 1FF0h) must be read at the beginning of the alarm updating routine. If not, the AF flag will never be released, and the TIMEKEEPER will continuously output an interrupt to the MCU, and the system will become jammed. SOFTWARE CONFIGURATION The program is listed on page 4. To understand its operation, it is important to distinguish between the three pointer variables, pointing to physical addresses in the hardware:
*TKPER_AL_HOUR, *TKPER_AL_MIN, *TKPER_AL_SEC
and the three integer variables, used as work-space by the software:
alarm_hour, alarm_minute, alarm_second
The first three variables are pointers to the physical address of the values that are stored in the M48T59 memory device. The three software variables are used to hold the user's data (they specify the period of the alarm in hours, minutes and seconds). This is not the same information as is stored in the TIMEKEEPER registers, as pointed to by the pointer variables, but is used in their calculation. The program does make use of the four Repeat bits (RPT4, RPT3, RPT2 and RPT1) that are physically located in the TIMEKEEPER device. These should all be set, except for those corresponding to fields that contain significant data. For instance, to set an alarm that repeats every 3 minutes and 45 seconds, the alarm_minutes and alarm_seconds variables would be loaded with these two values. Then appropriate values would be calculated for loading in the "Alarm Minutes" and "Alarm Seconds" fields of the alarm registers (at addresses 1FF3h and 1FF2h, *TKPER_AL_MIN and *TKPER_AL_SEC, respectively), and their Repeat bits (RPT2 and RPT1, respectively) would be reset to `0'. Meanwhile, the alarm_hour variable, and the "Alarm Date" and "Alarm Hour" fields of the alarm registers (at addresses 1FF5h and 1FF4h, *TKPER_AL_DATE and *TKPER_AL_HOUR, respectively) would be treated as "Don't Care", as
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indicated by their Repeat bits (RPT4 and RPT3, respectively) being set. This is summarized in Table 2, with the three local integer variables, alarm_second, alarm_minute and alarm_hour, used to represent the period. Table 2. Bit Setting to Control the Period of the Repeated Alarm
RPT4 1 1 1 1 RPT3 1 1 1 0 RPT2 1 1 0 0 RPT1 1 0 0 0 1 second alarm_second seconds (less than 1 minute) alarm_minute minutes alarm_second seconds (less than 1 hour) alarm_hour hours alarm_minute minutes alarm_second seconds (less than 1 day) Periodic alarm activated every
For example, to set a period of 1 hour 49 minute 35 seconds, the procedure is as follows:
RPT4 = 1 RPT3 = RPT2 = RPT1 = 0 alarm_second = 0x35 alarm_minute = 0x49 alarm_hour = 0x01
Or, to set a period of 49 minute 35 seconds, the procedure is as follows:
RPT4 = RPT3 = 1 RPT2 = RPT1 = 0 alarm_second = 0x35 alarm_minute = 0x49 alarm_hour = DontCare
SOFTWARE IMPLEMENTATION TIMEKEEPER Data Format TIMEKEEPER data is held as BCD (binary coded decimal). This is handled in the C programming language using the `unsigned char' data type. This can be converted within the C program to other data types, such as `integer', for numeric processing. Two functions are provided in the program at the end of this document for making this conversion. - Char_To_Int: to take a BCD parameter, and to return the equivalent integer value - Int_To_Char: to take an integer parameter, and to return the equivalent BCD value. The valid ranges for the alarm fields are summarized in Table 3. Table 3. TIMEKEEPER Data Format
Data C language type Alarm second Alarm minute Alarm hour Int (integer) Decimal 0-59 0-59 0-12 Char (character) Hexadecimal 00-3B 00-3B 00-0B Char (character) BCD 0-59 0-59 0-12
Alarm Update Management When the alarm signal is generated by the TIMEKEEPER device, it is communicated to the MCU. The MCU can monitor for this event either by polling, or by using interrupts. There are two variants of each method:
s
Polling
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- Read the flag register and check the AF bit (bit 6 of the register at offset 1FF0h) - Output the alarm signal on the TIMEKEEPER IRQ pin (pin 26), and read it on the MCU I/O port
s
Interrupts - Give priority to processing the alarm interrupt - The alarm signal is used to cause a wake up event
The last option is ideally suited when power consumption is the critical issue. For instance, when measuring, processing and storing some metering data every three minutes, the MCU can stay in its stand-by state for 95% of the time, and only run at full speed, with high power consumption, during the other 5% of the time. The other interrupt option is ideally suited when service time is the critical issue. The MCU will be interrupted from whatever processing it was currently engaged in, to service the alarm event. This can be integrated into a hierarchy of prioritized interrupts. The two polling options are equally suited when the MCU needs to run at full speed, and full power, all of the time, executing important background work, only responding to the alarm event when it has nothing else to do. In polling method, the MCU is always running full speed and full power consumption. In this case, the application power consumption is not a key issue and/or the process to be executed due to an alarm which has no priority. The alarm check and update is served as every other application routine. The TIMEKEEPER IRQ pin (pin 26) is an active low signal. In the following program, a routine "Update_Next_Alarm" is provided to take care of the periodic update of the alarm parameters. The program has been written in ANSI C, and has been compiled and tested with an M68HC11 series MCU.
/* TIMEKEEPER ; M48T59/59Y PERIODIC ALARM SOURCE CODE : /* Version: 1.01 */ */
/****************************************************************************/ /* Copyright (c) 1999 STMicroelectronics. */ /* */ /* This program is provided "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER */ /* EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO, THE IMPLIED WARRANTY */ /* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK */ /* AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE */ /* PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, */ /* REPAIR OR CORRECTION. */ /****************************************************************************/ /****************************************************************/ /* */ /* This program controls the TIMEKEEPER alarm hardware so */ /* as to provide the functionality of a periodic alarm. */ /* */ /****************************************************************/ #include #include // this was developed on HC11 platform // M88 Flash+PSD register map
extern volatile unsigned char dip_sw; /*****************************************************************/ /* TIMEKEEPER memory map */ /* Depend on your system and your TIMEKEEPER. */ /* The device is M48T59 series, 8kx8 non volatile SRAM, 16 clock */ /* alarm registers in address 1FF8h to 1FFFh */ /* In this example, the TIMEKEEPER was mapped from 4000h to 5FFFh*/ /*****************************************************************/
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/* #ifndef _MEM_MAP_H #define _MEM_MAP_H #define #define #define #define #define #define #define #define #define #define #define EXT_RAM_BASE (unsigned int) TIMEKEEPER_HOUR (unsigned char *) TIMEKEEPER_MIN (unsigned char *) TIMEKEEPER_SEC (unsigned char *) TIMEKEEPER_CAL (unsigned char *) TKPER_AL_IT (unsigned char *) TKPER_AL_DATE (unsigned char *) TKPER_AL_HOUR (unsigned char *) TKPER_AL_MIN (unsigned char *) TKPER_AL_SEC (unsigned char *) TKPER_FLAG (unsigned char *) 0x4000 0x5FFB 0x5FFA 0x5FF9 0x5FF8 0x5FF6 0x5FF5 0x5FF4 0x5FF3 0x5FF2 0x5FF0
#endif */ /*****************************************************************/ /* function Char_To_Int */ /* description : This function convert the timekeeper data*/ /* (in BCD format) to an integer. */ /* input : char byte */ /* output : integer */ /* example : octet = 0x33 (51 in integer) */ /* Char_To_Int = 33 (0x21 in hexa) */ /*****************************************************************/ int Char_To_Int(unsigned char octet) { int buffer; buffer = (int)(octet); if (octet <= 0x09) return(buffer); if ((octet >= 0x10) & (octet <= 0x19)) return (buffer-6); if ((octet >= 0x20) & (octet <= 0x29)) return (buffer-12); if ((octet >= 0x30) & (octet <= 0x39)) return (buffer-18); if ((octet >= 0x40) & (octet <= 0x49)) return (buffer-24); if ((octet >= 0x50) & (octet <= 0x59)) return (buffer-30); } /*****************************************************************/ /* function Int_To_Char */ /* description : This function convert an integer data */ /* to BCD TIMEKEEPER format (unsigned char) */ /* input : int integ */ /* output : unsigned char */ /* example : integ = 33 (0x21 in hexa) */ /* Int_To_Char = 0x33 (51 in integer) */ /*****************************************************************/ unsigned char Int_To_Char(int integ) { char buffer; buffer = (unsigned char)(integ); if (integ <= 9) return(buffer); if ((integ >= 10) & (integ <= 19)) return (buffer+6); if ((integ >= 20) & (integ <= 29)) return (buffer+0x0C); if ((integ >= 30) & (integ <= 39)) return (buffer+0x12); if ((integ >= 40) & (integ <= 49)) return (buffer+0x18); if ((integ >= 50) & (integ <= 59)) return (buffer+0x1E); } /*****************************************************************/ /* void Update_Next_Alarm */ /* description : After alarm interupt, it will : */ /* - reset the TIMEKEEPER IT flag */ /* - read the actual time in the clock register */ /* - calculate the next alarm time */ /* - update the alarm register */ /* to prepare for the next alarm */ /* input : alarm period (al_hour, al_minute, al_second) */ /* output : nothing */
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/*****************************************************************/ void Update_Next_Alarm(int al_hour,int al_minute,int al_second) { // time carry, going to be used for hour, minute and second // calculation process. unsigned char time_flag = 0; // intermediate storage for alarm data. int buffsec; int buffmin; int buffhour; // temporary storage unsigned char buffchar; // Touch the flag register to reset TIMEKEEPER AF flag (interupt) buffchar = *TKPER_FLAG; /*****************************************************************/ /* This is to update the alarm second register. */ /* It will test if RPT1 is set. If not then it adds "al_second" */ /* to second alarm register. It takes care of the minute carry. */ /*****************************************************************/ if (!(*TKPER_AL_SEC & 0x80)) // if !RPT1 { // update register with carry buffsec = Char_To_Int(*TIMEKEEPER_SEC) + al_second; if (buffsec > 59) // if >59 { // then restore 60sec format *TKPER_AL_SEC = Int_To_Char(buffsec-60); time_flag = 1; } else *TKPER_AL_SEC = Int_To_Char(buffsec); // normal case } /*****************************************************************/ /* This is to update the alarm minute register. */ /* It will test if RPT2 is set. If not then it adds "al_minute" */ /* to alarm minute register. It takes care of the hour carry. */ /*****************************************************************/ if (!(*TKPER_AL_MIN & 0x80)) // if !RPT2 { // update register with carry buffmin = Char_To_Int(*TIMEKEEPER_MIN) + al_minute + time_flag; if (buffmin > 59) // if >59 { // then restore 60 min format *TKPER_AL_MIN = Int_To_Char(buffmin-60); time_flag = 1; } else { *TKPER_AL_MIN = Int_To_Char(buffmin); // normal case time_flag = 0; } } /*****************************************************************/ /* This is to update the alarm hour register. */ /* It will test if RPT2 is set. If not then it adds "al_hour" to */ /* alarm hour register */ /*****************************************************************/ if (!(*TKPER_AL_HOUR & 80)) { buffhour = Char_To_Int(*TIMEKEEPER_HOUR) + al_hour + time_flag; if (buffhour > 23) *TKPER_AL_HOUR = Int_To_Char(buffhour-24); else *TKPER_AL_HOUR = Int_To_Char(buffhour); } }
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main(void) { int alarm_second; int alarm_minute; int alarm_hour;
// relative alarm variable
/*****************************************************************/ /* TIMEKEEPER alarm configuration example. */ /*****************************************************************/ *TKPER_AL_HOUR *TKPER_AL_MIN *TKPER_AL_SEC alarm_hour alarm_minute alarm_second &= 0x7F; &= 0x7F; &= 0x7F; = 1; = 49; = 35; // // // // // // // // Memory-mapped unsigned char pointers to the external hardware registers to set a one-off alarm for a fixed time today. Local memory integer variables to hold the repetition period for an alarm (& an interrupt on pin 26) every 1hr 49min 35sec (for example).
// Start the Timekeeper oscillator. *TIMEKEEPER_SEC &= 0x7F; // RPT4 set *TKPER_AL_DAY |= 0x80; // enable IRQ request on pin26 (M48T59) *TKPER_AL_IT |= 0x80; while (1) { /*******************************************************************/ /* read_the_port is a read of MCU I/O to detect an alarm interrupt */ /* lcd_min_display is a lcd software driver used for routine debug */ /* Those library were developed for FLASH+PSD development board. */ /*******************************************************************/ read_the_ports(); lcd_min_display(0,3,*TIMEKEEPER_HOUR); // display current time lcd_min_display(0,7,*TIMEKEEPER_MIN); lcd_min_display(0,13,*TIMEKEEPER_SEC); if (dip_sw==0x0E) // dip_sw is updated by read_the_port // if detect alarm interrupt from TIMEKEEPER
{ Update_Next_Alarm(alarm_hour,alarm_minute,alarm_second); lcd_min_display(1,3,*TKPER_AL_HOUR); lcd_min_display(1,7,*TKPER_AL_MIN); lcd_min_display(1,13,*TKPER_AL_SEC); } } } // display next alarm time
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