0
\$\begingroup\$

For some ADCs and DACs I'm using I need a 24.576MHz clock (96kHz * 256). Obviously I can use a low jitter audio clock generator. However, I have a AM335x processor available that claims to have a low jitter clock (ADPLLJ). Could I use this clock? It appears that it can be divided and multiplied to reach that frequency and it would save some trouble of getting a clock generator and a crystal oscillator if I could use this low jitter clock. The clock is explained in the AM437x reference manual. The clock also exists on the AM335x but the reference manual only mentions it briefly.

AM437x AM335x

\$\endgroup\$
0
\$\begingroup\$

Well, it seems you can't.

I guess you'll use McASP0 or McASP1 to drive the DAC/ADC. Their clock is derived from either CLK_M_OSC (the oscillator output, so no PLL) or CORE_CLKOUTM4/2 aka L3S_CLK (see page 4549, also confirmed by table Table 8-23 page 1143). This clock is itself derived from ADPLLS (see page 1141), not ADPLLLJ. ADPLLLJ feeds some other perpherals (see page 1144).

\$\endgroup\$
5
  • \$\begingroup\$ I see, thanks for the help! @dim I am using McASP0 as a SPDIF audio transmitter and receiver. But I can use the McASP1 clock for sure. However I have another question. I have a somewhat large number of ADCs and DACs. I'm using the PCM4201 and PCM4202 ADCs, and the PCM1789 and PCM1690 DACs. They all use a audio serial port protocol made by texas instruments. Could I configure the GPIO of the AM355x to transmit and receive this data? \$\endgroup\$ Apr 23 '16 at 3:36
  • \$\begingroup\$ I think transmiting serial data over gpio is very impractical. This may even be impossible if the frequency is too high, and anyway, it will slow down the proc a lot. However, the am33x has PRUs that you can maybe configure to do that. I don't know much about them however. \$\endgroup\$
    – dim
    Apr 23 '16 at 6:57
  • \$\begingroup\$ Yeah, I think the best solution is to use an FPGA to interface with the data converters and interface the FPGA with the processor. \$\endgroup\$ Apr 23 '16 at 9:59
  • \$\begingroup\$ If you have lots and lots of DAC/ADC, yes, but honestly, have a look at the PRUs, I seem to remember they were designed for this kind of cases, so it might be enough for your needs. \$\endgroup\$
    – dim
    Apr 23 '16 at 10:11
  • \$\begingroup\$ I'll look into that. They have enough pins for sure. \$\endgroup\$ Apr 23 '16 at 10:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.