VS1005 Max Freq while using Ethernet

[ottinger]

I looked around the VS1005 Datasheet and it looks at first glance that both USB and Ethernet are only available when the Core is clocked at 60 Mhz. Is this Info correct?? Because the Datasheet is not 100% coherent - USB 60 Mhz is only mentioned in the Overview - whereas Ethernet is only mentioned in the Peripherals-Section. (or vice-versa)

best wishes, Georg

[Panu]

Yes, that is correct. Unfortunately, when USB or Ethernet or both is active, then the only acceptable frequency is 60 MHz. We needed to make this choice, otherwise the clocking of the IC would have been exceedingly difficult (there are 5 clock domains already) and the price would have been considerably higher.

For your reference, MP3 decoding needs about 20 MHz and the peripheral FIFO buffer helps with data transfers, so there's still some MHz to spare, even with Ethernet or USB.

Here is a chart of the clocking options for VS1005. We feel that most applications need standard sample rates (48 kHz, 96 kHz etc) in the S/PDIF and I2S ports, so we recommend that you use 12.288 MHz crystal for the VS1005. But you may need to use 12.000 MHz if you need to use FM radio together with USB or Ethernet.

VS1005 Crystal Options

vs05clk.png (14.27 KiB) Viewed 2098 times

When you use FM Radio, the freely adjustable RFVCO clock source is used by the FM radio receiver, and the only option to provide cpu clock is to use the PLL clock multiplier, with which you can only have 0.5 x XTAL steps for the CPU clock rate, so 60.000 MHz is not possible with 12.288+PLL: You would need the RFVCO to provide 60.000 Mhz with 12.288 XTAL, but the RFVCO is used by the FM radio.

Some VS1005 peripherals like USB, Ethernet, Nand flash, SD card are in the fast peripherals domain, which has its clock sourced from the CPU core clock, and others are in the crystal domain (DAC, ADC, S/PDIF, I2S) which provides extremely stable, jitter-free clock. The most demanding peripherals are USB and Ethernet, which need to run at a specific high frequency, and of course the FM radio, which needs to run at exactly the received radio channel's frequency.

-Panu