[SeaBIOS] [Mohon Peak] Console output behavior before and after call to int19h

[Patrick Agrain]

Hello,

Purpose:
Get the output sent through int10h on an external serial link mapped on 
MEM space (PCIe board with OxPCIe952 from Startech).

Hardware:
Mohon Peak CRB with coreboot. PCIe board with OxPCIe952 from Startech. 
Bootable hard disk with GRUB and Linux.

Code flow: (from my understanding)
<...>
./src/post.c: mainint()
                             |--> interactive_bootmenu()
                             |                   |--> "Press ESC for 
boot menu." (sent through INT10h calls)
                             |
                             |--> startBoot()
                                                  |--> "Jump to int19"
                                                  |--> Call INT19h

<INT19h handler>
./src/boot.c: do_boot()
                            |--> "Booting from Hard Disk..." (sent 
through INT10h calls)
                            |--> boot_disk()
                            |--> Call INT13h
<...>

What works:
Modified seabios to initialize PCIe board OxPCIe952.
- Add field at the end of BDA to store the u32 base address of the 
additional UART ports.
- Init the bridge after pci_probe().
- Store the base address of the additional UART ports during serial_setup().
Using sgabios with output set to 0x2f8 (uart1) works flawlessly.
- All (dprintf-based) messages are sent on second UART port of the Mohon 
Peak.
- All (printf-based, INT10h) messages are also displayed on second UART 
port of the Mohon Peak.
- System boots.

What almost works:
Modified sgabios to display INT10h calls on MEM mapped UART port.
- All (dprintf-based) messages are still sent on second UART port of the 
Mohon Peak.
- Display of "Press ESC for boot menu." on OxPCIe952 : OK (any previous 
INT10h-based messages also displayed on OxPCIe952).
- After call of INT19h, "Booting from Hard Disk..." is not displayed on 
OxPCIe952.
- Mohon Peak remains in POST code F8h (like as for waiting a selection 
in the GRUB menu).

Note: reducing debug level (20 -> 2) of int10h shows that the 
int10h-handler is called with the messages to be displayed, but nothing 
appears on OxPCIe952 side.

What could be the reason of this behavior ?
Any switch between 16-bit and 32-bit code execution ?

Any suggestion is welcome.
Regards,
Patrick Agrain