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  • 【AMBA-1】APB协议

      APB(Advanced Peripheral Bus),外围总线的意思。该总线协议是ARM公司提出的AMBA总线结构之一,几乎已成为一种标准的片上总线结构。APB可以向上连接至AHB-Lite和AXI总线。APB的每个传输都在时钟上升沿处罚,每个传输至少消耗两个时钟周期。Amba 3新加入了PREADY和PSLVERR。

      1、Amba 3 APB的信号列表如下表:

    Signal

    Source

    Description

    PCLK

    Clock source APB Clk

    PRESETn

    System bus equivalent

    Reset. The APB reset signal is active LOW. This signal is normally connected directly to the system bus reset signal.

    PADDR APB bridge

    Address. This is the APB address bus. It can be up to 32 bits wide and is driven by the peripheral bus bridge unit.

    PSELx APB bridge

    Select. The APB bridge unit generates this signal to each peripheral bus slave.It indicates that the slave device is selected and that a data transfer is required.There is a PSELx signal for each slave.

    PENABLE APB bridge

    Enable. This signal indicates the second and subsequent cycles of an APB transfer.

    PWRITE APB bridge

    Direction. This signal indicates an APB write access when HIGH and an APB read access when LOW.

    PWDATA APB bridge

    Write data. This bus is driven by the peripheral bus bridge unit during write cycles when PWRITE is HIGH. This bus can be up to 32 bits wide.

    PREADY Slave interface Ready. The slave uses this signal to extend an APB transfer.
    PRDATA Slave interface

    Read Data. The selected slave drives this bus during read cycles when PWRITE is LOW. This bus can be up to 32-bits wide.

    PSLVERR Slave interface

    This signal indicates a transfer failure. APB peripherals are not required to support the PSLVERR pin. This is true for both existing and new APB peripheral designs. Where a peripheral does not include this pin then the appropriate input to the APB bridge is tied LOW.

    2、 APB总线的状态转移图

                       apb

      IDLE:状态机默认状态;

      SETUP:有传输发生后就转到此状态,对应的PSELx被选中,该状态通常持续一个时钟周期,在下个上升沿进入ACCESS;

      ACCESS:PENABLE信号使能,从SETUP到ACCESS,PADDR、PSELx、PWRITE、PWDATA的值须保持稳定不变。来自Slave的PREADY信号控制从ACCESS状态向下转变,PREADY=0,继续保持在ACCESS状态,延长ACCESS以等待Slave;PREADY=1,若没有其他传输,直接进入IDLE,若有后续传输,则直接进入SETUP状态。

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  • 原文地址:https://www.cnblogs.com/wisdomjoyce/p/3601494.html
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