In this blog, the eBoot menu is modified to to allow user selection of Clearing of the Hive or not. This is implemeneted by adding a further parameter to the BOOT_CG and BSP_ARGS structures to handle the boolean selection. The eBoot code is then extended to pass the selection up to the OS args driver. The OS args driver then is modified to get the value when requested by getting it from the structure passed to it through shared memory. This replaces the use of the dummy variable s_bClearHive as used in args.c in the previous blog.
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The previous blog in this series demonstrated how to add a custom OAL IOCTL to the BSP. In particular it implemented the IOCTL_HAL_GET_HIVE_CLEAN_FLAG IOCTL so that it returns a fixed value to the OS when called. In this blog, that code is extended to call the BSP boot args using a custom boot arg. A fixed value is returned by boot args in this case. A later blog will pass that arg from eboot.
OAL IOCTLs are callable from OAL code to perform specific functions within the OS Kernel. The OS requires the OEM to specifically implement certain IOTLCs that it calls, and some other standard IOTCLs if implemented are automatically called by the OS. One such optional IOCTL, IOCTL_HAL_GET_HIVE_CLEAN_FLAG, will cause the OS to clear the hive registry if it passes back a TRUE when called at OS startup. These IOCTLs are normally called in kernel mode as they are called directly by the the kernel. Some IOCTLs can be called by a user mode thread as well. In our book, Professional Windows Embedded Compact 7, I covered implementing a custom OAL IOCTL for the VCEPC BSP. This blog looks at adding an OAL IOCTL with the ARM TI AM335X BSP