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--- soc:2008:stefanha:journal:week5 [2008/06/24 05:34]
stefanha
+++ soc:2008:stefanha:journal:week5 [2008/06/30 10:03] (current)
stefanha
@@ Line 29: / Line 29: @@
 **Noticed that "Linux Device Drivers, Third Edition" is free**.  See [[http://lwn.net/Kernel/LDD3/|here]].  Some of the book applies to gPXE since our code is often inspired or based off the Linux kernel.
-Next steps:
+**The b44 cannot access memory above 1 GB**.  We need a workaround that allocates descriptor rings and IO buffers from memory below 1 GB.  We hit this issue today when dmb tested the driver on his machine with 2 GB memory.  I have a temporary hack to place the gPXE heap at 4 MB into the address space.  Need to talk to mentors about a long term solution.
-  * [b44] Can DMA memory ever be allocated from >1GB?
-  * [b44] Cleanup & testing.
+==== Wed Jun 25 ====
-  * [GDB] Update [[:dev:gdbstub|GDB stub page]] and screencast when UDP code is merged into mainline.  See [[http://grub.enbug.org/DebuggingWithGDB|GRUB GDB wiki page]] for inspiration.
+**Tested and sent bzImage patch for review**.  The bzImage patch updates gPXE lkrn images to a modern Linux kernel image format.  It also includes a fix for zImage loading in gPXE and allows Lilo to load gPXE lkrn images.
-  * [GDB] Real-mode remote debugging.
+**Currently investigating a solution to the b44 1 GB memory limitation**.  Will also continue simplifying the driver.  While testing, dmb mentioned it downloaded images slowly so I may work on the performance.  I did not port the performance optimizations in the Linux driver, so there is plenty of low-hanging fruit.
+==== Fri Jun 27 ====
+**Linux DMA mapping as a solution to driver memory constraints**.  The b44 driver can only access the first gigabyte of memory.  When I asked how to work around this limitation, mcb30 suggest looking at Linux ''pci_map_single()''.  I am going to implement something similar to manage bounce buffers for devices that cannot access gPXE's heap.
+==== Sat Jun 28 ====
+Git commit:
+  * [[http://git.etherboot.org/?p=people/stefanha/gpxe.git;a=commit;h=3c923c79098190c12b686965d8bd48e1cedecd4d|[b44] DMA mapping for device address limitations]]
+  * [[http://git.etherboot.org/?p=people/stefanha/gpxe.git;a=commit;h=87455683845a6694fdc89cf986caa50571be8ef0|[b44] Fix DMA mapping]]
+**Working on DMA mapping**.  I have designed and implemented DMA mapping for gPXE, see commits above.  The b44 driver uses DMA mapping to work around the chip addressing limitations.  I am currently writing tests.
+I am not done with the code but wanted to commit instead of keeping this out of tree.  Before submitting the code for review I will break it up into several patches:
+  * **uhmalloc**, general-purpose external memory allocator.  Separates the ''umalloc'' heap from its memory allocator (which I call ''uhmalloc'').  The idea is that DMA mapping reuses ''uhmalloc'' to manage its DMA heap.
+  * **DMA mapping** for transparently managing bounce buffers when needed by hardware.  The DMA mapping API provides a way to structure DMA transactions.  If the hardware has addressing limitations and is unable to access gPXE's heap, bounce buffers are used to communicate via regions of memory that the device has access to.
+  * **b44 with DMA mapping**.  Update b44 code using DMA mapping API so it runs on machines with more than 1 GB of RAM.  This reverses the hack to place the gPXE heap at 4 MB into the physical address space.
+===== Next week =====
+On to [[.:week6|Week 6]]!

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