To effectively communicate with hardware, system software needs a way to access a device’s internal registers and storage locations to control its behavior, check its status, or deliver data. To make this possible, these internal device locations must be assigned specific addresses from one of the address spaces supported by the system. Here is a […]

When a computer first powers up or undergoes a reset, the system software actually knows very little about the hardware connected to it. To establish communication, configuration software must systematically scan the PCI Express (PCIe) fabric to discover the machine’s topology, a process known as enumeration. Here is a step-by-step walkthrough of how system software

In our previous lectures on PCI Express (PCIe) configuration, we learned that only the Root Complex is permitted to originate Configuration Requests. This strict rule prevents chaos by ensuring the system processor maintains absolute control over configuring devices and assigning resources. But once the Root Complex generates a Configuration Request, how does that packet successfully

In our exploration of PCI Express (PCIe) architecture, we have established that devices use configuration space to achieve a “plug-and-play” environment. However, an important rule governs this space: only the Root Complex is permitted to originate Configuration Requests. This restriction ensures that the system processor acts as the central authority, preventing the anarchy that would

In the early days of PCs, installing a new expansion card meant manually configuring physical switches and jumpers to assign resources, which frequently resulted in frustrating hardware conflicts. The original PCI architecture solved this by introducing a standardized “Plug and Play” mechanism known as Configuration Address Space. As the industry transitioned to PCI Express (PCIe),

To effectively manage and communicate with all the different components inside a computer, the system needs a reliable way to identify exactly where each component is located within the system’s topology. In the PCI Express (PCIe) architecture, every single function is uniquely identified by a combination of its Bus number, Device number, and Function number.

In our final deep dive into the PCIe layered architecture, we reach the foundation: the Physical Layer. This is the lowest hierarchical layer, responsible for taking the fully assembled packets from the Data Link Layer and transforming them into the raw electrical signals that physically travel across the wire. Here is a breakdown of how

In our previous lectures on the PCI Express (PCIe) layered architecture, we discussed how the Transaction Layer builds data packets and how Flow Control prevents buffer overflows. However, as high-speed serial data physically travels across the Link, it is susceptible to transient electrical noise and interference. To guarantee that Transaction Layer Packets (TLPs) survive this

In our previous lecture, we explored how the Transaction Layer assembles our data into Transaction Layer Packets (TLPs). Once a TLP is built, it must safely survive the physical journey across the PCIe connection. This crucial responsibility falls to the Data Link Layer, which serves as the highly reliable middleman between the Transaction Layer above

In our continued exploration of the PCIe Transaction Layer, we must address how the system handles competing types of data. Unlike legacy shared buses where data is generally handled strictly on a first-come, first-served basis, PCIe was designed from its inception to support time-sensitive transactions. For applications like streaming audio or video, data delivery must