Feb 4, 2013 · It uses a full PCIe 5.0 x16 link, allowing for a theoretical bidirectional 32 GT/s, but with multiple TB of memory behind a buffer controller. In much the same way that companies like Samsung pack NAND into a U.2-sized form factor, with sufficient cooling, Samsung does the same here but with DRAM.

Dec 10, 2020 · It is not "PCIE memory", but it is a memory device in the system that is accessible by other devices and therefore needs to be seen across the bus. It is entirely possible that the majority of the memory is reserved for the microcontroller to work from, and that a small patch of memory is available for the system to read the captured sensor data.

Dec 9, 2019 · Consider the alternative of having lots of DRAM for volatile memory like usual. The OS can use it for caching. You still could have a LVM cache disk, but maybe just a high endurance, low latency NVMe to eat the writes.

Oct 22, 2012 · Your interpretation of the BAR setup is correct. Then how does it differ. The device's on board memory/registers usually is a special RAM, it may be bi-port RAM (when each cell has two ports one is connected to the host bus, another to the device's internal bus, this allows faster and concurrent access from both sides), it may be a registers or even directly some inputs or outputs of some FPGA ...

That if a PCI device wishes to transfer data to a memory address, that address must exist in actual system RAM (and is allocated during PCI configuration) and not virtual memory. So if a PCI device only needs to transfer a small amount of data at a time, where there is no advantage to putting it into RAM or using DMA, then I/O addressing is ...

Oct 18, 2015 · The PCI/PCIe adapter can gain control of the bus, and compete for memory cycles. The CPU, the DMA controller and bus masters could all be competeing for memory access. The memory arbiter typically favors the CPU, …

Memory-mapped I/O uses the same address bus to address both memory and I/O devices – the memory and registers of the I/O devices are mapped to (associated with) address values. So when an address is accessed by the CPU, it may refer to a portion of physical RAM, but it can also refer to memory of the I/O device.

Aug 9, 2017 · On x86 PCs, the memory space is shared in the system. System memory maps from the bottom up (0 -> xGB) & PCI memory space is in the upper part of system memory space (xxx --> FFFFFFFF 4GB-1). Note that "memory space" is not "memory". It's just address ranges for HW to decode & claim transactions.

I understood that a PCI Express endpoint device may have some memory BAR mapped in the system memory (is it always RAM the system memory we are talking about?). I need to understand what happens when I send from the CPU to the device (A) a memory read request, addressing a certain memory address (first memory BAR, offset 0).

Jun 10, 2016 · Additionally, this will generally be a physical memory address, not a virtual memory address. The Linux kernel will arbitrate access to these devices with functions such as mmap() that allow the mapping of physical memory to virtual memory addresses. For example, say you have a PCIe device that controls 8 LEDs.