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x86: Enable debug UART for Minnowmax

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Enable the debug UART and emit a single 'a' early in the init sequence to
show that it is working.

Unfortunately the debug UART implementation needs a stack to work. I cannot
seem to remove this limitation as the absolute 'jmp %eax' instruction goes
off into the weeds.

So this means that the character output cannot be any earlier than
car_init_ret, where memory is available for a stack.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
This commit is contained in:
Simon Glass 2015-08-02 18:07:21 -06:00
parent 74356d7fb1
commit bbbe55f6f2
2 changed files with 13 additions and 0 deletions
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9
arch/x86/cpu/start.S
View file

@ -128,6 +128,15 @@ car_init_ret:
andl $0xfffffff0, %esp
post_code(POST_START_STACK)
/*
* Debug UART is available here although it may not be plumbed out
* to pins depending on the board. To use it:
*
* call debug_uart_init
* mov $'a', %eax
* call printch
*/
/* Zero the global data since it won't happen later */
xorl %eax, %eax
movl $GENERATED_GBL_DATA_SIZE, %ecx

4
configs/minnowmax_defconfig
View file

@ -24,3 +24,7 @@ CONFIG_FRAMEBUFFER_VESA_MODE_11A=y
CONFIG_DM_RTC=y
CONFIG_USE_PRIVATE_LIBGCC=y
CONFIG_SYS_VSNPRINTF=y
CONFIG_DEBUG_UART=y
CONFIG_DEBUG_UART_NS16550=y
CONFIG_DEBUG_UART_BASE=0x3f8
CONFIG_DEBUG_UART_CLOCK=1843200