SD Card failing 'disk_initialize' in standalone mode

[Eric P]

Posted on August 11, 2017 at 03:25

I have an ST STM32F405 microprocessor. I generated my IAR Embedded Workbench 7.4 files using STM32 Cube software.  I'm trying to use the SD card resources to access a micro SD card on our custom board. When I use the debugger in IAR it can access the SD card and the data files on-board no problem. However, as soon as I disconnect the debugger and run in standalone mode, I can't access the SD card. I have traced it to a failure of function disk_initialize in the diskio.c file. When it runs the command:

stat = disk.drv[pdrv]->disk_initialize(disk.lun[pdrv]);

I get a value of 0 when it succeeds and the debugger is attached. But a value of 1 when running in standalone mode.

I read online that perhaps the SDIOCLK divide factor should be changed from 1 to 4 <= but I did that and it did not help.  I'm not sure what else to check.

How can I debug this?

[Eric P]

Posted on August 11, 2017 at 14:54

Some more information on this.  I probed the CLK pin on the SD card with an oscilloscope.  When I run with the debugger, it oscillates at 8 MHz.  However, when I run in standalone mode, it is oscillating at 400 kHz.  This is likely the problem.  Any idea why the clock responds differently in the two cases and, more importantly, how I can guarantee a clock rate?