[MinnowBoard] Early serial output

[Ma, Maurice]

Hi, Simon,

Just want to make sure that you are talking about the MinnowBoard (TunnelCreek + TopCliff), not MinnowBoard Max (Baytrail), right?

For MinnowBoard Max,  I have tested and the early serial port does work before the FSP API call.

For MinnowBoard, the serial port is from UART0 on TopCliff(EG20T).   In order to enable early console in coreboot,  
you need to initialize the TopCliff UART 0 and then call console_init() in romstage  after FSP TempRamInit() and before FspInit().  

The standard linux UART driver for EG20T is open,   you can refer to :
http://lxr.free-electrons.com/source/drivers/tty/serial/pch_uart.c

You just need to implement the standard RX and TX function for Coreboot.   It should be straight forward.  
Please note, since the EG20T UART is on PCI bus and the PCI bus is not enumerated yet at early boot stage.   So you need to assign temporary bus and PCI MMIO resource to the bridges and the UART controller before accessing the UART registers.                                    

Thanks
Maurice

-----Original Message-----
From: Hawley, John 
Sent: Tuesday, January 20, 2015 3:07 PM
To: MinnowBoard Development and Community Discussion
Cc: Ma, Maurice
Subject: Re: [MinnowBoard] Early serial output

Maurice might have an answer on this for you.

Thanks!

- John 'Warthog9' Hawley

On 1/17/2015 7:09 PM, Simon Glass wrote:
> Hi,
> 
> I see in coreboot there is code to print UART messages in the 
> romstage, but nothing appears until romstage_main_continue() is 
> called. This is quite late - both the CAR init and FSP init have 
> completed by this point.
> 
> Is there any way to get earlier serial output? I don't think the board 
> has visible POST codes so serial seems to be the only option.
> 
> Regards,
> Simon
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