[MinnowBoard] Early serial output

Simon Glass sjg at chromium.org
Thu Jan 22 04:52:05 UTC 2015

Hi Maurice,

On 21 January 2015 at 13:18, Simon Glass <sjg at chromium.org> wrote:
> Hi Maurine,
> On 20 January 2015 at 18:02, Ma, Maurice <maurice.ma at intel.com> wrote:
>> 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.
> Yes i it Minnowboard Max. It sounds like you are saying I should get
> serial output early in romstage, but I don't. Do I need to enable
> something?

Just to follow up, I got this working. It seems there is quite a long
list of init to be done to get the serial working. But I have early
output running now. Thanks for your help.



More information about the elinux-MinnowBoard mailing list