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9boot: Add the *nouartbios parameter

Some BIOS emulates the screen output redirecting it
to the serial port, and using the BIOS functions at
the same time that the emulation generates some problems.
The new parameter *nouartbios remove any use of the BIOS
to access the uart.

--- a/sys/man/8/9boot

+++ b/sys/man/8/9boot

@@ -188,7 +188,7 @@

 .B console=

 but the parameters are ignored as BIOS allows

 only a maximum baud-rate of 9600 so the setting

-.B "b9660 l8 s1"

+.B "b9600 l8 s1"

 is assumed.

 Some BIOS emulate/redirect keyboard input

 and CGA output to the serial console,

@@ -198,6 +198,11 @@

 and

 .B *nocga=

 parameters.

+Also,

+in some of these emulations the BIOS uart functions

+can produce some problems that can be avoided using the

+.B *nouartbios=

+parameter.

 Serial console is not supported by EFI.

 .PP

 .B 9bootfat

--- a/sys/src/boot/pc/sub.c

+++ b/sys/src/boot/pc/sub.c

@@ -297,7 +297,9 @@

 			nocga = 1;

 		if(memcmp("*nokbd", line, 6) == 0)

 			nokbd = 1;

-		if(memcmp("console", line, 8) == 0)

+		if (memcmp("*nouartbios", line, 11) == 0)

+			uart = -2;

+		if(memcmp("console", line, 8) == 0 && uart != -2)

 			uartconf(p);

 		s = confend;

@@ -504,7 +506,7 @@

 {

 	if(*s >= '0' && *s <= '3'){

 		uart = *s - '0';

-		uartinit(uart, (7<<5) | 3);	/* b9660 l8 s1 */

+		uartinit(uart, (7<<5) | 3);	/* b9600 l8 s1 */

 	} else

 		uart = -1;

 }

-- 

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