I am trying to interface the ADS1278 with the AM3358. The ADS1278 would be configured for frame sync discrete format and high speed mode and running from an external oscillator (I would like to get as close as possible to the full 144531sps of the ADS1278). The MCASP on the AM335X only has 4 serializers, so for this to work I need to use both MCASP modules. This is where things get interesting. I can't get a pin mux that gives me all four serializers in addition to the receive section clocks, so it looks like I would need to run the MCASP in synchronous mode and use the transmit section to receive the high speed clock and generate both the bit clock and frame sync.
I can provide schematics if requested, but the basic gist of what I want to do is below:
high speed clocks: external oscillator drives MCASP0_AHCLKX and MCASP1_AHCLKX and CLK
bit clocks: MCASP0_ACLKX drives MCASP1_ACLKX and SCLK
frame sync: MCASP0_AFSX drives MCASP1_AFSX and FSYNC
data: DOUT[8:1] drives MCASP0_AXR[3:0] through MCASP1_AXR[3:0]
So my questions:
1. I am a little hesitant since I feel like I am combining several non standard usage scenarios to put this setup together (MCASP in synchronous mode without actually transmitting and externally slaving the MCASP1 clocks to MCASP0). Is there any reason why the above setup shouldn't work? Has anybody tried this combination before?
2. While investigating I starting playing with the pin mux utility to assist the hardware design but I am having difficulty with an I/O subset violation on MCASP1. I need to pin out MCASP1_AHCLKX, MCASP1_ACLKX, MCASP1_AFSX, and MCASP1_AXR[3:0]. I can get everything else, but when I add MCASP1_AXR1 it causes an I/O subset violation. My understanding is that this warning means the timing has not been characterized/closed for that pin selection. In this particular case, the bit clock really isn't that fast (a couple MHz depending on my AHCLKX to ACLKX ratio). I can share the pin mux design file if needed. Is this something I can reasonably ignore or should I be concerned about it?
