From bbbe55f6f25e686ad799c2a70aa941eeb276adb6 Mon Sep 17 00:00:00 2001 From: Simon Glass Date: Sun, 2 Aug 2015 18:07:21 -0600 Subject: x86: Enable debug UART for Minnowmax 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 Reviewed-by: Lukasz Majewski --- arch/x86/cpu/start.S | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/x86/cpu') diff --git a/arch/x86/cpu/start.S b/arch/x86/cpu/start.S index e5c1733..313fa3f 100644 --- a/arch/x86/cpu/start.S +++ b/arch/x86/cpu/start.S @@ -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 -- cgit v1.1