I have a Sparkfun RTC connected to a SAM7-MT256 dev board via the 5v supply and I2C interface. Everything works fine except it doesn’t keep very good time - even when continuously powered. I seem to loose about 10-12 seconds/day. This is not acceptable. I was hoping for more like 1-2 seconds /day or 1 min/month.
This problem was mentioned a while back here: [DS1307 Crystal Accuracy. However, there didn’t seem to be a resolution. It seemed to be an issue with the xtal on the board not having the correct capacitance.
I did try using the onchip RTT with compensation as outlined in an Atmel note, but that didn’t produce any better results and had no battery backup. Does anyone have any suggestions on how this problem may be overcome?