Intermittent Failures While Accessing CompactFlash Card

Description

The Nios II Development Kit version 5.0 and later includes a CompactFlash controller peripheral suitable for interfacing to CompactFlash cards in True IDE mode on Nios development boards. For True IDE mode to operate, CompactFlash cards require that the ATASEL_N input be driven to ground during power-up.

The CompactFlash controller peripheral includes a configurable power register, used to cycle power to CompactFlash cards from Nios II software through a metal oxide semiconductor field-effect transistor (MOSFET) on the Nios development boards. However, in certain development boards, power to the CompactFlash card does not turn off completely during this power cycle operation. Because of this condition, the CompactFlash might not sample the ATASEL_N pin during the power-cycle operation after FPGA configuration when this pin is driven to ground. Instead, the CompactFlash card might sample the ATASEL_N pin when power is first applied to the development board, when I/O is not yet driven by the FPGA (before FPGA configuration).

Resolution

If you encounter errors with CompactFlash when using the Nios development boards, try one of the following solutions:

• Use a different CompactFlash card. Certain cards are more susceptible to the power-cycling issue than others.
• Modify the Nios development board. This is recommended if you are familiar and comfortable with board-level modifications. Disconnect pin 9 (ATASEL_N) on the CompactFlash socket on your Nios development board and tie this pin to ground.

The CompactFlash socket uses a staggered numbering on the pins (starting from pin 1: 1, 26, 2, 27, ...); refer to the CompactFlash Association specification for right-angle surface-mount connectors for exact specifications on this connector. This modification permanently enables True IDE mode operation.