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9 Front kernel for the MediaTek MT7688
currently tested on;
Onion Omega 2
Hi-Link HKL7688A
FPU Emulation;
The MIPS24KEc core used in the MT7688 does
not have a FPU. Because of the way Mips
does branch delay slots, tos.h needs to
include a scratch space for fpimips.c
/* scratch space for kernel use (e.g., mips fp delay-slot execution) */
ulong kscr[4];
/* top of stack is here */
Since lots of things use tos.h, the enitre
spim environment needs to be nuked and reinstalled
to keep things consistent.
Build Environment;
Because libc for spim ends up using a combination
of portable code, and mips and spim machine specific
code, I have seen some issues where things being
built in the wrong order causes failure in the
kernel. For best results;
cd /sys/src
objtype=spim
mk nuke
mk libs
mk install
Drivers;
The first UART, often documented as
"UART Lite" or "UARTL", is set up, but no others.
The MT7688 has 1 Ethernet device wired directly
into a 7 port switch, usually on port 5. Port 0
is typically used as the WAN port on routers, and
ports 1-4 are the LAN ports.
Right now, the Ethernet driver, ether7688.c, just
sets up the switch to run ports 1-5 as a simple
unmanaged switch to allow outside connections.
This has been tested on the HKL7688A, but not on
the Onion Omega 2 with the Ethernet expansion.
WiFi, SPI, I²C, GPIO, USB, MMC, and a dedicated
switch driver are works in progress.
u-boot;
The kernel currently assumes that it will be
loaded at 0x80020000 and that plan9.ini will
be loaded at 0x80010000 (CONFADDR)
nvram;
In order to connect to your auth and fileserver,
copy a nvram with the credentials you want into
a file, and add the location of that file (ex. /usr/
glenda/nvram) to the bootdir section of the kernel
configuration file (mt7688).
In plan9.ini, specify to use the nvram in the
/boot directory in the kernel;
nvram=/boot/nvram
nvroff=0
nvrlen=512
Erratum 48;
There is a known issue with the 24K series cores,
where data is lost if 3 cache writes are done in
a row. The mips linker in some legacy Plan 9
distributions has a change in vl/noop.c where it
can be set to insert a no-op between stores to
avoid this issue.
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