AHB的slave地址采样的问题

jakeguo

在slave对master发出的地址进行采样，此时，需要HREADY为高还是没有要求？实在怀疑自己的理解能力。AMBA Spec中的原文“A slave must only sample the address and control signals and HSELx when HREADY is HIGH, indicating that the current transfer is completing. Under certain circumstances it is possible that HSELx will be asserted when HREADY is LOW, but the selected slave will have changed by the time the current transfer completes.(arm IHI 0011A   page 53)"
如果不是为高的话，那它在这里何必说这句话”A slave must only sample the address and control signals and HSELx when HREADY is HIGH“
但是在Spec的图中又这样表示，如图：

upsingmen

It is strongly recommended to sample adress & control signals from AHB-Bus when HREADY is high. the reason are :
1) as what the spec mentioned,  when HREADY is low, the master may assert the Hsel high level but now AHB-Bus maybe actually is in transfer for another Slave.
2) When Hready is High, indicating the current transfer is completing, so it is safe to sample the address and control information from AHB-Bus

you can take HHREADY  as a signal which Logical AND for output HHREADY from All slaves.
any questions about AHB and its Implementation, Please contact. robin.jiang.sh@gmail.com

jakeguo

It is strongly recommended to sample adress & control signals from AHB-Bus when HREADY is high. the  ...
upsingmen 发表于 2013-12-25 13:58

                               
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thanks a lot.

bangbangtang

hready信号要为高，从机才采样主机发出的地址和控制信息

asic_wang

AHB规范中强调，the valid address phase only lasts for just one cycle。
所以hready为high是采样是必须的，否则你采样的不是一个有效的address phase，那个有效的address phase就是以hready来标定的。
AMBA spec中有的时序图没有体现出这一点。

redleaf1988

正解！

glace12123

ARM总线里最重要的信号之一就是READY，先看看这个信号起到什么样的作用吧