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| author | Warner Losh <imp@FreeBSD.org> | 2022-08-26 21:47:21 +0000 |
|---|---|---|
| committer | Warner Losh <imp@FreeBSD.org> | 2023-01-24 21:49:32 +0000 |
| commit | adeec17f8122f9af4940e6e45391b38b377082c1 (patch) | |
| tree | 9a5ae68fec462576a7bd7bbc3f9594ff67cbffae | |
| parent | f80cdedebe9f10fe0e7cb0548c1ead0237c37d06 (diff) | |
| download | src-adeec17f8122f9af4940e6e45391b38b377082c1.tar.gz src-adeec17f8122f9af4940e6e45391b38b377082c1.zip | |
stand: Document that boot0 uses BIOS
And thus has a limited range of supported baud rates. Also add that
setting BOOT_BOOT0_COMCONSOLE_SPEED=0 will leave it unchanged which
sometimes can give you 115200 if the BIOS initialized things outside of
the normal BIOS baud rates (which many x86 enbedded-targetted boards
do).
Sponsored by: Netflix
Reviewed by: emaste, manu (earlier versions)
Suggestions by: jhb
Differential Revision: https://reviews.freebsd.org/D36300
(cherry picked from commit 7ed3228323ef4f9e3130603ea68c3be9c2ed50ce)
| -rw-r--r-- | stand/i386/boot0/Makefile | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/stand/i386/boot0/Makefile b/stand/i386/boot0/Makefile index 82eb9eefee76..1453f17751b9 100644 --- a/stand/i386/boot0/Makefile +++ b/stand/i386/boot0/Makefile @@ -42,6 +42,13 @@ BOOT_BOOT0_ORG?= 0x600 ORG=${BOOT_BOOT0_ORG} # Comm settings for boot0sio. +# +# boot0sio uses BIOS INT $0x14 for serial ports, we can only support these +# baudrates due to INT14's limited interface. In addition, if +# BOOT_BOOT0_COMCONSOLE_SPEED=0, then the baud rate and frame format will remain +# unchanged. Some BIOSes initialize the serial ports to 115200, and this may +# allow boot0sio access at that rate if so. +# # Bit(s) Description # 7-5 data rate (110,150,300,600,1200,2400,4800,9600 bps) # 4-3 parity (00 or 10 = none, 01 = odd, 11 = even) |