[U-Boot] NS16550 Register structure

[Pedanekar, Hemant]

Wolfgang,

Yes, that is not just word-aligned, instead, the Dm6467 UART access need to be "Word LOAD/STORE". Thus, if I use STRB <THR> instead of STR <THR> to transmit a character, it doesn't work.

As you said, using prepad/postpad, we can define the alignment but my understanding is that the final register access will be byte access only as the register will be declared as "unsigned char". 

For generating 32-bit load/store, probably we need to declare register members as "unsigned long". Or can we achieve the same without any code changes?

Thanks
-
Hemant
 

> -----Original Message-----
> From: Wolfgang Denk [mailto:wd at denx.de]
> Sent: Tuesday, January 05, 2010 1:05 PM
> To: Pedanekar, Hemant
> Cc: u-boot at lists.denx.de; dzu at denx.de
> Subject: Re: [U-Boot] NS16550 Register structure
> 
> Dear "Pedanekar, Hemant",
> 
> In message <2A3DCF3DA181AD40BDE86A3150B27B6B03094B2982 at dbde02.ent.ti.com>
> you wrote:
> >
> > I have observed that in the recent commit (file include/ns16550.h), the
> ns16550 UART register structure declaration is changed so that
> irrespective of the CONFIG_SYS_NS16550_REG_SIZE setting the register
> access will be done at byte level.
> 
> This seems to be working on all systems so far, which is not so much
> of a surprise as the registers are 8 bit wide only.
> 
> > This crates problem when UART space access is required to be word-
> aligned. I am particularly referring to DaVinci DM6467, where STRB over
> UART register space is not supported and requires 32-bit access (L/STR).
> 
> Please make sure to use exact terms. Alignment is one thing, and  bus
> width  is  another  one.  Alignment  can be easily adjusted using the
> prepad_* or postpad_* settings.
> 
> > If I go ahead and add a specific handling in ns16550.h file (structure
> register members as "long"), I would end up making code similar to the one
> earlier to last commit. Is there a better way to handle such case?
> 
> No such changes should be needed, as far as I understand the code.
> 
> Best regards,
> 
> Wolfgang Denk
> 
> --
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