plan 9 on pi



			    mkf




			  ABSTRACT

	  Tips for running plan	9 on raspberry pi




Raspberry pi is	a single board computer	made by	raspberry pi
foundation  somewhere  in UK. In 2012(?) Richard miller	have
made the plan 9, this is known as miller's pi. at some point
9front have imported miller's code.  9front have since got a
64-bit version of bcm kernel.	this  guide  covers  9front,
more info on miller's is appercited.

1.  installtion

As time	of writing by default  9front  ships  with  hjfs  on
installation  image and	that image is sized 2Gb.  You can dd
(or cp,	or whatever your prefered method may be)  that	into
your sdcard.  That's all.

Resizing the paritions

Hjfs however does not support growing a	parition (gefs seems
to  be the only	file system capable of doing so), Thus to do
so. you	may need to do a  classic  installation,  there	 are
many  ways for it; but the easiest way is to install using a
usb thumb drive.

    copy 9front	image into your	sdcard,	we need	to do  this
     since we need to have the kernel and boot blobs

    then copy same thing into your sdcard, for file  system
     contents

    boot the pi, select	the usb	in bootargs

    run	inst/start, make the partitions	as you would on	the
     sdcard, and install.





		     November 23, 2024






			   - 2 -


2.  ISSUES

audio

Raspberry Pi is	odd, audio hardware in	pi  is	perhaps	 the
most odd part of it.  Use usb audio cards if you can, but if
you can't:

1.   3.5MM jack	uses a PWM connected to	arm core, and offers
     poor  quality.   However  it is much simpler to write a
     driver for.  Load on  cpu	sometimes  casues  noticable
     effects on	PWM, and thus results in audiable and annoy-
     ing noises.

2.   HDMI audio	is much	more sophisticated (or horribly	com-
     plex,  depending on your point of view), and uses a RPC
     protocol to  communicate  with  broadcom  core.   which
     makes writing drivers much	harder offers better audio.

There are two  drivers	for  PWM,  one	is  located  under
/n/extra/src/audiobcm.tgz  and	said to	be working for first
pi (bcm2385).  I haven't tested	it, but	PWM audio  interface
have  been  realtively	same  since bcm2385 (with some minor
improvments) from arm core's view point.

3.  Wireless

9front has recently added support for raspberry	 pi's  wifi.
this  supports	3+  and	 zero  2.  zero	 too should work but
requires changes to kernel.  On	pi 3 and zero, wireless	card
is  ether0.  source code for wireless driver is	available in
 /sys/src/9/bcm/ether4330.c

4.  USB

It's widely believe before raspberry  pi  4  (that  includes
zero  2), they had nasty USB controllers, while	they may (is
there a	case otherwise?) work well for keyboard, mouses	 and
thumb  drives,	they  may  not	work as	well as	expected for
devices	that need more power.

Also note that,	USB controller can crash (is it	 a  hardware
limit?)	 if  it	 gets  too hot,	using a	heat sink and fan is
recommended if you are you are going to	use  that  raspberry
pi's USB (which	sadly, also includes ethernet, since it	uses
USB).

5.  UART

6.  Compiling a	kernel

Kernels	for pi port are	located	under	 /sys/src/9/bcm	 for
32-bit	port  (all  raspberry pis) and	/sys/src/9/bcm64 for
64-bit kernel (late revisions of pi 2, pi zero 2  and  pi  3


		     November 23, 2024






			   - 3 -


and newer)

  # 32 bit kernels (work on 64 bit pis as well)
  cd /sys/src/9/bcm
  mk 'CONF=pi'
  mk 'CONF=pi2'

  # 64 bit kernels:
  cd /sys/src/9/bcm64
  mk 'CONF=pi3'	# for pi 3
  mk 'CONF=pi4'	# for pi 4


7.  HDMI

Raspberry pi uses HDMI	for  video  output.  thankfully	 (or
not),  Firmware	 capable of handling framebuffer, and we use
that.  the only	drawback there is we can't change resolution
during run-time.  to change it,	first mount  pidos partition
(on 64-bit kernels you may need	to mount  dos instead):

  ; 9fs	pidos

And then add the following into	your  config.txt file:

  [all]
  hdmi_blanking=1
  hdmi_group=2
  hdmi_mode=51
  framebuffer_depth=32


First line means this configuration will be applied  to	 all
raspberry  pi  models. This is handy for when you share	same
sd card	between	several	boards.	  hdmi_blanking	 will  blank
your  monitor when not in use, see  mouse(3) man page to see
how to use it.	The lines  hdmi_group  and    hdmi_mode	 are
used  to  set type of display (TV or monitor) and resolution
of such.  see raspberry	pi  documention	 for  more  info  on
those.	 Lastly	   framebuffer_depth is	for amount of colors
you have,  32 means 32-bit color, default value	is  16.















		     November 23, 2024