Re: uhci driver question

On Wed, 17 Oct 2007, jidong xiao wrote:

> Hi,Alan,
>   I saw a macro called MAX_PHASE is defined as 32, but I don't know
> what does this macro mean and why is it be set to 32?

MAX_PHASE is the size of the load table.  It is set to 32 as a 
compromise; the natural table size of 1024 is much too big.  Also, 32 
is what other HCDs use.

> I also noticed struct uhci_hcd has an element of short
> load[MAX_PHASE], debugfs shows this array.
> 
> localhost:~ # cat /sys/kernel/debug/uhci/0000\:00\:1d.0
> Root-hub state: suspended   FSBR: 0
> HC status
>   usbcmd    =     0048   Maxp32 CF EGSM
>   usbstat   =     0020   HCHalted
>   usbint    =     0002
>   usbfrnum  =   (1)158
>   flbaseadd = 19493158
>   sof       =       40
>   stat1     =     0080
>   stat2     =     0080
> Most recent frame: 456 (86)   Last ISO frame: 456 (86)
> Periodic load table
>         0       0       0       0       0       0       0       0
>         0       0       0       0       0       0       0       0
>         0       0       0       0       0       0       0       0
>         0       0       0       0       0       0       0       0
> Total: 0, #INT: 0, #ISO: 0
> 
> 
> What does this "periodic load table" mean?

It is the number of microseconds allocated for periodic transfers
(Isochronous and Interrupt) during each frame (modulo 32).

Alan Stern


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