DMA Introduction

• intro & reference

  • 一個解釋 DMA 的故事: 瞭解 DMA (Direct Memory Access)

  • 英文 wiki: https://www.wikiwand.com/en/Direct_memory_access

• DMA 分為兩個種類

  • standard DMA (DMA Controller): 有 central 的 DMA Controller, DMA Controller 會提供 control register 來讓 CPU 進行讀寫, 用於指定 DMA copy 的記憶體位址.

  • bus mastering: CPU 跟每個 peripherals 都可以被授權來控制 memory bus. 因此 peripheral 能直接成為 bus master, 就能直接對 memory 進行讀寫.

• DMA Controller Example

  • 早期的(198x) IBM PC 使用 Intel 8237 作為 DMA controller.

  • Some Intel Xeon processor provide an embedded DMA controller called I/OAT.

• Bus Mastering Example

  • PCI bus

  • AMBA AHB bus

DMA on ARM platform

DMA in ARM bus system(AMBA)

• high-end (Cortex-A, Cortex-R)

  • DMA-330 Controllers (PL330, PrimeCell, CoreLink)

  • both high-end, high-performance AXI systems

  • AMBA-AXI protocol

  • AMBA-compatible peripheral

• low-end (Cortex-M, ARM9)

  • AMBA-AHB protocol

  • DMA Controller: PL230, PL080, PL081

  • AMBA AHB system support bus mastering DMA

ARM specs:

• linux kernel driver:

  include/linux/amba/bus.h
  include/linux/amba/pl330.h
  drivers/dma/pl330.c
  include/linux/amba/pl080.h
  

• reference

  • ARM - other system controllers

  • CoreLink controllers and peripherals

  • Testing VFIO_PLATFORM with the PL330 DMA Controller

AMBA bus

• version

  • AMBA v1: Advanced System Bus (ASB) and Advanced Peripheral Bus (APB)

  • AMBA v2: AMBA High-performance Bus (AHB) that is a single clock-edge protocol.

  • AMBA v3

    • AXI: higher performance interconnect. (than AHB?)

    • ATB(Advanced Trace Bus): part of the CoreSight on-chip debug and trace solution

  • AMBA v4: AXI4, ACE: system wide coherency.

  • AMBA v5: CHI (Coherent Hub Interface): re-designed high-speed transport layer and features designed to reduce congestion.

• thus, in version 5

  • bus protocol: AXI/AHB for high/low-end

  • cache coherence: AMBA5 CHI, AMBA 4 ACE

  • trace/debug: ATB

• ref

  • wiki: https://en.wikipedia.org/wiki/Advanced_Microcontroller_Bus_Architecture

  • ARM Announces AMBA 5 CHI Specification: www.arm.com/about/newsroom/arm-announces-amba-5-chi-specification-to-enable-high-performance-highly-scalable-system-on-chip.php