LDD Component

The LDD is a Processor Expert component, which is part of Freescale's HAL architecture. This component implements the actual hardware access to a particular device, and is capable to generate OS-specific codes. In the absence of an RTOS component, an LDD generates code for a bare-board device driver.

There are two main characteristics that distinguish an LDD component compared to other Processor Expert components:

• LDDs of a specific device share the same API, no matter what architecture they generate code for. For instance, Ethernet_LDD always contains a SendFrame() and ReceiveFrame() methods. They all work the same way no matter the platform they are executed on.
• Most LDD functions receive, at least, one LDD data structure pointer. This structure is used to perform the I/O, and varies depending on the device.

In OS with Virtual Interrupt Tables, ISRs receive input parameter structures. HAL also takes care of this, passing the LDD data structure in that case. If the OS does not handle a virtual interrupt table, it means ISR does not receive any parameter; ISR uses the LDD data structure that is declared a global variable.

An LDD comprises two internal parts:

• An LDD layer, in charge of implementing software algorithms, to handle the hardware. This layer is exposed to you through the LDD APIs.
• PDD layer. This is a set of calls to perform the low-level I/O interaction with the hardware.