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RTC millisecond register

DLR
Intellectual 260 points

Other Parts Discussed in Thread: TMS320C5515

I'm sort of not sure what to make of the RTC millisecond register.

Looking at document:

http://focus.ti.com/lit/ug/sprufo7/sprufo7.pdf

Then section 3 and register 0x1904 RTCMIL

 

 

Then I'm running code from this URL. I'm doing the C5515 eZdsp audio filiter demo code on my TMS320C5515 eZdsp USB stick.

http://code.google.com/p/c5505-ezdsp/

 

So I wanted to use the RTC to time some stuff but I would see some funny numbers from time-to-time. Then I found that in BCD format the so called milliseconds register actually has a range of 0000-1023. It seems to me if it was really milliseconds it would have a range of 000-999 BCD. So it seems the register really has a poor description.

So it seems like this should be called "ticks" to count to 1 second and not milliseconds if the range is 0-1023.

Even table 8 on page 18 says the BCD can be 1000.

  • 0
    TI__Mastermind 30561 points

    Hi DLR,

    You are correct about the RTCMIL register ranging from 0 - 1023.  All other units of time (seconds, minutes, etc.) are as you would expect.

    See the bullet that describes the RTCMIL Register just below Table 1 in Section 2.3.1 "Time/Calendar Data Format".

    "The RTC Milliseconds Register (RTCMIL) stores the milliseconds value of the current time. After the milliseconds count reaches 1023 then the seconds register is updated by one. The reason for the rollover occurring at 1024, rather than 1000, is due to the crystal's oscillation frequency being a power of two, 32.768kHz. 32768 / 1024 = 32 clocks per 'millisecond'. Thus, calling this register a 'milliseconds' register is a bit of a misnomer. The milliseconds digit 3 is 1 bit and the milliseconds digits 2:0 are 4 bits; digits 3:0 are encoded BCD values 0000 (0b 0000b 0000b 0000b) through 1023 (1b 0000b 0010b 0011b)."

    Also, if you are using the C5515 DSP, you should refer to the C5515 Documentation instead of the VC5505 Documentation.

    See http://focus.ti.com/docs/prod/folders/print/tms320c5515.html#Application Notes

    Hope this helps,
    Mark