What is the sampling frequency for the DM365 internal Voice Codec?
I'm in little trouble.
8 or 16 kHz? 16..48kHz? Any?
1) 8kHz or 16kHz ? (only one of two?)
1a) DM365 DataSheet (Rev. November2010)
page 201
“Sampling frequency: 8 KHz or 16 KHz ”
1b) DM36x Voice Codec User's Guide (SPRUFI9B - Rev. Jul.2010)
page 9, page 11, page 12
“Sampling frequency: 8 KHz or 16 Khz ”
But, There are no any fields in any voice codec registers where we can switch 8 or 16 kHz.
Instead of this, we can see that 'Fs' is derived from VoiceCodec Operational Frequency as
Fs = VC_Freq / 256
VoiceCodec Frequency is derived from PLL2controller via PPL2C.DIV4 and PERI_CLKCTL .DIV2 dividers.
2) 16kHz ... 48kHz ?
DM36x ARM Subsytem User's Guide (SPRUFG5A - Rev.Aug.2009)
page 33, Section 5.2.4
“The voice codec module supports the sampling frequency (Fs) from 16 KHz to 48 KHz. ”
3) Any?
DM36x ARM Subsytem User's Guide
page 33, Section 5.2.4
“...
voice codec clock to be same or close to 256xFs.
• Voice codec clock frequency = PLLC2SYSCLK4/(DIV2+1)
”
Hmmm...
As I understand (look at the formula above) the value of 'DIV2' is value from PERI_CLKCTL (0x01C40048) register bits 15:7 (see page 148, section 9.12.19) and the 'PLLC2SYSCLK4' is frequency in Hz.
PLLC2SYSCLK4 freq = PLL2freq / (DIV4+1)
where 'DIV4' is value from PLLC2_PLLDIV4 register (0x01C40C00+0x160). See page 63, section 6.6.22.
Well...
The final formula for sampling frequency is...
Fs = ( ( PLL2freq / (DIV4+1) ) / (DIV2 +1) ) / 256
where:
-
Fs – sampling frequency (Hz) for voicecodec;
-
PLL2freq – frequency of PLL2-out (Hz);
-
DIV4 – value from PLLC2_PLLDIV4 (0x01C40C00+0x160) register, bits 4..0, and bit15=1(enable);
-
DIV2 – value from PERI_CLKCTL (0x01C40048) register, bits 15:7.
It's a correct? Can you confirm this?
If this is correct, then I can write any value in these dividers.
For example.
If PPL2freq=594MHz and DIV4=9 (value from 0x01C40C00+0x160 is 0x8009), DIV2=3 (bits 15:7 from 0x01C40048 is equal to '000000011') then...
Fs = 594MHz / (9+1) / (3+1) / 256 = 594MHz / 10 / 4 / 256 = 58 007 Hz =~ 58kHz
is sampling frequency for voicecodec will be 58 kHz ?
It's a correct?
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With impatience I wait for an answer!
