✎ soc:2010:andreif:journal:week2

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===== Week 2 [ 31 May - 6 Jun 2010 ] =====

==== Day 1 [ 31 May 2010 ] ====

Git commit: [[http://git.etherboot.org/?p=people/andreif/gpxe.git;a=commit;h=318ca039b7381e67e04f92447d9b2a211fe9541a|318ca039b7381e67e04f92447d9b2a211fe9541a]]

Today was about reorganizing parts of what I've written so far and taking some time to analyze things and try to see the big picture. Also, I did some debugging in the Linux driver (insert printks, make modules, make modules_install, modprobe -r pcnet32, modprobe pcnet32) and found out that even that one takes an unneeded branch at one point and tries to modify some registers that aren't available on older chips. Since the datasheets say that accessing inexistent registers might summon some nasty demons, I avoided this in my code. It could be that those accesses do some undocumented stuff, but for now I'll keep this in mind and see how things turn out when the driver is all done.

Other than that, I'm all set up for tackling the transmit and receive parts, which I'll start tomorrow.

==== Day 2 [ 1 Jun 2010 ] ====

Git commit: [[http://git.etherboot.org/?p=people/andreif/gpxe.git;a=commit;h=04d57225b1c06fa6c37f7565ed9b2977580a29e0|04d57225b1c06fa6c37f7565ed9b2977580a29e0]]

As I suspected, the transmit and receive were easier than the NIC's setup. I managed to implement both of them today, following the r8169 driver source code.

Transmit works by first giving you an //struct io_buffer//. It is the transmit routine's responsibility to fill the current available descriptor's fields with the iobuf's parameters (length, start address). Then you have to change the descriptor's ownership to 1 to signal that
it now contains valid information and the NIC should send the data that it describes. After this, the routine forces the NIC to send any new valid descriptors by setting the TDMD (Transmit Demand) bit. I suppose it works without this setting since the datasheet mentions that there is a poll-time counter that eventually elapses. In the end, all you have to do is make sure that the circular descriptor buffer is handled, by advancing the cursor and increasing the number of descriptors in use.

The .poll routine has to check first if there are any new received frames or if some frames have finished being transmitted by the NIC.
  * The transmitted frames now have the OWN bit from the descriptor set to 0 thus signalling that the NIC is done with their processing. To cleanup the buffer, it uses the //netdev_tx_complete()// routine, resets the descriptor, advances the tail of the circular buffer and decreases the total used descriptor count.
  * The received packets have a similar fate. One of the differences is the fact that you have to see if there weren't any errors in the frame's receival such as a CRC, framing or overflow errors. If there is such an error, the frame is discarded using //netdev_rx_err//. If there was no error first use //iob_put// to adjust the iobuffer's length if required and finally send the frame to the upper layers using //netdev_rx//. Since the buffer is out of our hands now the driver is free to remove any references it might have had to it and clear the descriptor, plus advance the cursor. As a result, the driver has to allocate new buffers for all the descriptors that were valid and which got their frames sent to the upper layers. This is the final thing the driver has to do.

After all this was done, I tested the driver on my VMWare setup, and after fixing some bugs I managed to get it working. In the end, I've booted a DSL using my driver :) Yay.

In the next few days I'll spend some time cleaning up the code and rearranging stuff.

==== Day 3 [ 2 Jun 2010 ] ====

me.rest()

==== Day 4 [ 3 Jun 2010 ] ====

Git commit: [[http://git.etherboot.org/?p=people/andreif/gpxe.git;a=commit;h=5dbf33bdc89da087fe86f4a20973b648c6372837|5dbf33bdc89da087fe86f4a20973b648c6372837]]

Back to work! Reorganized some bits of the code, some comments, etc. I have some doubts regarding the way the code handles full-duplex negotiation and multiple PHYs and most likely my driver does not handle these issues correctly ATM. I'll post the driver up for some reviews,
see what people think.

Tomorrow I'll try and setup QEmu and VirtualBox environments, to test the driver there too.

==== Day 5 [ 4 Jun 2010 ] ====

Git commit: These are not the commits you are looking for :waves hand:

Today didn't yield much in terms of code but I did manage to do some testing. First I set up QEmu and ran this small test:
<code>
qemu -net nic,model=pcnet -net user -bootp http://vmsplice.net/tinycore.gpxe -option-rom bin/pcnet32.rom
</code>
It worked, no problems there.

After that, I started setting up VirtualBox. I ran into some problems because of the already inserted kvm module, which I had to remove, after which VirtualBox worked. Since I didn't have a -bootp option like QEmu and I wanted to play with the gPXE command line, I used that one to do the exact test that I did in qemu. <code>
ifopen net0
dhcp net0
imgfetch http://vmsplice.net/tinycore.gpxe
imgload tinycore.gpxe
imgrun tinycore.gpxe
</code>
This worked on both of the pcnet NICs that VirtualBox emulates.

I started coding after that, when I realized that I forgot about the patches regarding the MAC address checking routines (is_valid_ether_addr & friends). Did two small patches and emailed them. If those get accepted I can easily finish the address checking in my pcnet32 driver.

Unfortunately, I didn't get to go through the feedback on the driver or start working on the link state code. Slow day :(

==== Day 6 [ 5 Jun 2010 ] ====

Git commit: [[http://git.etherboot.org/?p=people/andreif/gpxe.git;a=commit;h=551178b108b99374d6918ec7fdc92b8eee8bd47e|551178b108b99374d6918ec7fdc92b8eee8bd47e]]

I started today by looking at the link state code in the Linux driver. The problem with it is that it depends on the number of PHYs and the duplex mode of the NIC. The size of the code is comparable to that of some of my other main routines, but I find that its impact is minimal. I decided that for now I would leave link state on in .probe and implement it if someone specifically requests it.

Testing followed. Mdc and stefanha both told me to try and download some images larger than 100MB to see what speeds the driver reaches and how it performs. The old driver got an 100MB image in 178s my driver got it 145s. Something was wrong. Thanks to mdc, meteger and stefanha the bug eventually surfaced and got fixed. I was writing some wrong values into the CSR0 register. After this, the driver got the 100MB image in 37s. The following days I'll try to improve this. I'll post some comparisons tomorrow.

After a wonderful meeting with stefanha and mdc, I got back to fixing the stuff people told me about in the email thread. In the process, I managed to read (skipping some sections) this [[http://www.rdrop.com/users/paulmck/scalability/paper/whymb.2009.04.05a.pdf|paper]]. I'll go through it tomorrow too to make sure I fully understand the concepts.

==== Day 7 [ 31 May 2010 ] ====

me.rest()
Trace: • ubuntu_iscsi • usb_gpxe_design • audit-the-shifts • 2008 • elf-ebi-initramfs-lnxi-howto • fedora11bko • debian_lenny_iscsi
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