Add README for tutorial 10_DMA_memory

10_DMA_memory/README.md

@@ -1,13 +1,245 @@
 # Tutorial 10 - DMA Memory
 
-Coming soon!
+There's a secret I haven't told you! A certain part of our code doesn't work
+anymore since the [virtual memory](../0D_virtual_memory) tutorial. There is a
+regression that manifests in the `Videocore Mailbox` driver. It will only work
+until **paging and caching** is switched on. Afterwards, the `call()` method
+will fail. Why is that?
 
-This lesson will teach about:
-- Simple bump memory allocators and non-cacheable memory.
-- Using MiniUart for early boot messages and dynamically switching to the PL011
-  Uart later (which now needs the memory allocator that theoretically could fail
-  - which the MiniUart could then print).
+The reason is that in our code, the RPi's processor is sharing a `DRAM buffer`
+with the `Videocore` device. In other words, the concept of **shared memory** is
+used. Let's recall a simplified version of the protocol:
 
+1. RPi `CPU` checks the `STATUS` MMIO register of the `Videcore` if a message can
+   be written.
+2. If so, `CPU` writes the address of the `DRAM buffer` in which the actual
+   message is stored into the `Videocore`'s `WRITE` MMIO register.
+3. `CPU` checks the `STATUS` and `READ` MMIO registers if the Videocore has
+   answered.
+4. If so, `CPU` checks the first `u32` word of the earlier provided `DRAM buffer`
+   if the response is valid (the `Videocore` puts its answer into the same buffer
+   in which the original request was stored. This is what is commonly called
+   a `DMA` transaction).
+
+At step **4**, things break. The reason is that code and **page tables** were
+set up in a way that the `DRAM buffer` used for message exchange between `CPU`
+and Videcore is attributed as _cacheable_.
+
+So when the `CPU` is writing to the buffer, the contents might not get written
+back to `DRAM` in time before the notification of a new message is signaled to
+the Videocore via the `WRITE` MMIO register (which is correctly attributed as
+device memory in the page tables and hence not cached).
+
+Even if the contents would land in `DRAM` in time, the `Videocore`'s answer
+which overwrites the same buffer would not be reflected in the `CPU`'s cache,
+since there is no coherency mechanism in place between the two. The RPi `CPU`
+would read back the same values it put into the buffer itself when setting up
+the message, and not the `DRAM` content that contains the answer.
+
+![DMA block diagram](../doc/dma_0.png)
+
+The regression did not manifest yet because the Mailbox is only used before the
+paging caching is switched on, and never afterwards. However, now is a good time
+to fix this.
+
+## An Allocator for DMA Memory
+
+The first step is to introduce a region of _non-cacheable DRAM_ in the
+`KERNEL_VIRTUAL_LAYOUT` in `memory.rs`:
+
+```rust
+Descriptor {
+    name: "DMA heap pool",
+    virtual_range: || RangeInclusive::new(map::virt::DMA_HEAP_START, map::virt::DMA_HEAP_END),
+    translation: Translation::Identity,
+    attribute_fields: AttributeFields {
+        mem_attributes: MemAttributes::NonCacheableDRAM,
+        acc_perms: AccessPermissions::ReadWrite,
+        execute_never: true,
+    },
+},
+```
+
+When you saw the inferior performance of non-cacheable mapped DRAM compared to
+cacheable DRAM in the [cache performance tutorial](../0E_cache_performance)
+earlier and asked yourself why anybody would ever want this: Exactly for the
+use-case at hand!
+
+Theoretically, some linker hacks could be used to ensure that the `Videcore` is
+using a buffer that is statically linked to the DMA heap pool once paging and
+caching is turned on. However, in real-world kernels, it is common to frequently
+map/allocate and unmap/free chunks of `DMA` memory at runtime, for example in
+device drivers for DMA-capable devices.
+
+Hence, let's introduce an `allocator`.
+
+### Bump Allocation
+
+As always in the tutorials, a simple implementation is used for getting started
+with basic concepts of a topic, and upgrades are introduced when they are
+needed.
+
+In a `bump allocator`, when a requests comes in, it always returns the next
+possible aligned region of its heap until it runs out of memory. What makes it
+really simple is that it doesn't provide means for freeing memory again. When no
+more memory is left, game is over.
+
+Conveniently enough, [Rust already provides memory allocation APIs](https://doc.rust-lang.org/alloc/alloc/index.html). There is an
+[Alloc](https://doc.rust-lang.org/alloc/alloc/trait.Alloc.html) and a
+[GlobalAlloc](https://doc.rust-lang.org/alloc/alloc/trait.GlobalAlloc.html)
+trait. The latter is intended for realizing a _default allocator_, meaning it
+would be the allocator used for any standard language construtcs that
+automatically allocate something on the heap, for example a
+[Box](https://doc.rust-lang.org/alloc/boxed/index.html). There can only be one
+global allocator, so the tutorials will make use of it for cacheable DRAM later.
+
+Hence, for the DMA bump allocator,
+[Alloc](https://doc.rust-lang.org/alloc/alloc/trait.Alloc.html) will be
+used. What is also really nice is that for both traits, only the `alloc()`
+method needs to be implemented. If this is done, you automatically get a bunch
+of additional default methods for free, e.g. `alloc_zeroed()`.
+
+Here is the implementation in `memory/bump_allocator.rs`:
+
+```rust
+pub struct BumpAllocator {
+    next: usize,
+    pool_end: usize,
+    name: &'static str,
+}
+
+unsafe impl Alloc for BumpAllocator {
+    unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
+        let start = crate::memory::aligned_addr_unchecked(self.next, layout.align());
+        let end = start + layout.size();
+
+        if end <= self.pool_end {
+            self.next = end;
+
+            println!(
+                "[i] {}:\n      Allocated Addr {:#010X} Size {:#X}",
+                self.name,
+                start,
+                layout.size()
+            );
+
+            Ok(NonNull::new_unchecked(start as *mut u8))
+        } else {
+            Err(AllocErr)
+        }
+    }
+
+    // A bump allocator doesn't care
+    unsafe fn dealloc(&mut self, _ptr: NonNull<u8>, _layout: Layout) {}
+}
+```
+
+The `alloc()` method returns a pointer to memory. However, it is safer to
+operate with [slices](https://doc.rust-lang.org/alloc/slice/index.html), since
+they are intrinsically bounds-checked. Therefore, the `BumpAllocator` gets an
+additional method called `alloc_slice_zeroed()`, which wraps around
+`alloc_zeroed()` provided by the `Alloc` trait and on success returns a `&'a mut
+[T]`.
+
+### Global Instance
+
+A global instance of the allocator is needed, and since its methods demand
+_mutable references_ to `self`, it is wrapped into a `NullLock`, which was
+introduced in the [last tutorial](../0F_globals_synchronization_println):
+
+```rust
+/// The global allocator for DMA-able memory. That is, memory which is tagged
+/// non-cacheable in the page tables.
+static DMA_ALLOCATOR: sync::NullLock<memory::BumpAllocator> =
+    sync::NullLock::new(memory::BumpAllocator::new(
+        memory::map::virt::DMA_HEAP_START as usize,
+        memory::map::virt::DMA_HEAP_END as usize,
+        "Global DMA Allocator",
+    ));
+
+```
+
+## Videocore Driver
+
+The `Videocore` driver has to be changed to use the allocator during
+instantiation, and in contrast to earlier, this could fail now:
+
+```rust
+let ret = crate::DMA_ALLOCATOR.lock(|d| d.alloc_slice_zeroed(MBOX_SIZE, MBOX_ALIGNMENT));
+
+if ret.is_err() {
+    return Err(());
+}
+```
+
+## Reorg of the Kernel Init
+
+Since the `Videcore` now depends on the `DMA Allocator`, its initialization must
+now happen _after_ the `MMU init`, which turns on **paging and caching**. This,
+in turn, means that the `PL011 UART`, which is used for printing and needs the
+`Videcore` for its setup, has to shift its init as well. So there is a lot of
+shuffling happening.
+
+In summary, the new init procedure would be:
+
+1. GPIO
+2. MMU
+3. Videcore
+4. PL011 UART
+
+That is a bit unfortunate, because if anything goes wrong at `MMU` or
+`Videocore` init, we can not print any fault info on the console. For this
+reason, the `MiniUart` from the earlier tutorials is revived, because it only
+needs the `GPIO` driver to set itself up. So here is the revamped init:
+
+1. GPIO
+2. MiniUart
+3. MMU
+4. Videcore
+5. PL011 UART
+
+Using this procedure, the `MiniUart` can report faults for any of the subsequent
+stages like`MMU` or `Videocore` init. If all is successful and the more capable
+`PL011 UART` comes online, we can let it conveniently replace the `MiniUart`
+through the `CONSOLE.replace_with()` scheme introduced in the [last tutorial](../0F_globals_synchronization_println).
+
+### Make it Fault
+
+If you feel curious and want to put all the theory to action, take a look at the
+code in `main.rs` for the DMA allocator instantiation and try the changes in the
+comments:
+
+```rust
+/// The global allocator for DMA-able memory. That is, memory which is tagged
+/// non-cacheable in the page tables.
+static DMA_ALLOCATOR: sync::NullLock<memory::BumpAllocator> =
+    sync::NullLock::new(memory::BumpAllocator::new(
+        memory::map::virt::DMA_HEAP_START as usize,
+        memory::map::virt::DMA_HEAP_END as usize,
+        "Global DMA Allocator",
+        // Try the following arguments instead to see the PL011 UART init
+        // fail. It will cause the allocator to use memory that is marked
+        // cacheable and therefore not DMA-safe. The communication with the
+        // Videocore will therefore fail.
+
+        // 0x00600000 as usize,
+        // 0x007FFFFF as usize,
+        // "Global Non-DMA Allocator",
+    ));
+```
+
+This might only work on the real HW and not in QEMU.
+
+## QEMU
+
+On the actual HW it is possible to reprogram the same `GPIO` pins at runtime to
+either use the `MiniUart` or the `PL011`, and as a result the console output of
+both is sent through the same USB-serial dongle. This is transparent to the
+user.
+
+On QEMU, unfortunately, two different virtual terminals must be used and this
+multiplexing is not possible. As a result, you'll see that the QEMU output has
+changed in optics a bit and now provides separate views for the two `UARTs`.
 
 ## Output
 

10_DMA_memory/src/main.rs

@@ -49,10 +49,9 @@ static DMA_ALLOCATOR: sync::NullLock<memory::BumpAllocator> =
         memory::map::virt::DMA_HEAP_END as usize,
         "Global DMA Allocator",
         // Try the following arguments instead to see the PL011 UART init
-        // fail. It will cause the allocator to use memory that are marked
-        // cacheable and therefore not DMA-safe. The answer from the Videocore
-        // won't be received by the CPU because it reads an old cached value
-        // that resembles an error case instead.
+        // fail. It will cause the allocator to use memory that is marked
+        // cacheable and therefore not DMA-safe. The communication with the
+        // Videocore will therefore fail.
 
         // 0x00600000 as usize,
         // 0x007FFFFF as usize,

doc/dma_0.svg

@@ -0,0 +1,402 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="870"
+   height="180"
+   viewBox="0 0 230.18749 47.625001"
+   version="1.1"
+   id="svg8"
+   inkscape:version="0.92.3 (2405546, 2018-03-11)"
+   sodipodi:docname="dma_0.svg"
+   inkscape:export-xdpi="95.999992"
+   inkscape:export-ydpi="95.999992">
+  <defs
+     id="defs2">
+    <marker
+       inkscape:stockid="Arrow2Lstart"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lstart"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         id="path2173"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(1.1,0,0,1.1,1.1,0)"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lend"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lend"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         id="path2176"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lend"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="marker1253"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         id="path1251"
+         style="fill:#ff6600;fill-opacity:1;fill-rule:evenodd;stroke:#ff6600;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:isstock="true"
+       style="overflow:visible"
+       id="marker1193"
+       refX="0"
+       refY="0"
+       orient="auto"
+       inkscape:stockid="Arrow2Lend">
+      <path
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         style="fill:#cc0000;fill-opacity:1;fill-rule:evenodd;stroke:#cc0000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         id="path1191"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:isstock="true"
+       style="overflow:visible"
+       id="marker1768"
+       refX="0"
+       refY="0"
+       orient="auto"
+       inkscape:stockid="Arrow2Lend">
+      <path
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         style="fill:#669900;fill-opacity:1;fill-rule:evenodd;stroke:#669900;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         id="path1766"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lend"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="marker1415"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         id="path1413"
+         style="fill:#808080;fill-opacity:1;fill-rule:evenodd;stroke:#808080;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)"
+         inkscape:connector-curvature="0" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lstart"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lstart-5"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         inkscape:connector-curvature="0"
+         id="path2173-4"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(1.1,0,0,1.1,1.1,0)" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lend"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lend-6"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         inkscape:connector-curvature="0"
+         id="path2176-8"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lstart"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lstart-5-5"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         inkscape:connector-curvature="0"
+         id="path2173-4-5"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(1.1,0,0,1.1,1.1,0)" />
+    </marker>
+    <marker
+       inkscape:stockid="Arrow2Lend"
+       orient="auto"
+       refY="0"
+       refX="0"
+       id="Arrow2Lend-6-6"
+       style="overflow:visible"
+       inkscape:isstock="true">
+      <path
+         inkscape:connector-curvature="0"
+         id="path2176-8-3"
+         style="fill:#000000;fill-opacity:1;fill-rule:evenodd;stroke:#000000;stroke-width:0.625;stroke-linejoin:round;stroke-opacity:1"
+         d="M 8.7185878,4.0337352 -2.2072895,0.01601326 8.7185884,-4.0017078 c -1.7454984,2.3720609 -1.7354408,5.6174519 -6e-7,8.035443 z"
+         transform="matrix(-1.1,0,0,-1.1,-1.1,0)" />
+    </marker>
+  </defs>
+  <sodipodi:namedview
+     id="base"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageopacity="0.0"
+     inkscape:pageshadow="2"
+     inkscape:zoom="0.99999999"
+     inkscape:cx="233.75149"
+     inkscape:cy="343.57437"
+     inkscape:document-units="mm"
+     inkscape:current-layer="layer1"
+     showgrid="true"
+     units="px"
+     showguides="true"
+     inkscape:snap-grids="true"
+     inkscape:snap-text-baseline="true"
+     inkscape:window-width="1920"
+     inkscape:window-height="1172"
+     inkscape:window-x="0"
+     inkscape:window-y="0"
+     inkscape:window-maximized="1">
+    <inkscape:grid
+       type="xygrid"
+       id="grid10" />
+  </sodipodi:namedview>
+  <metadata
+     id="metadata5">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(0,-249.37499)">
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:10.58333302px;line-height:1.25;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="103.18751"
+       y="56.229153"
+       id="text4524-3"><tspan
+         sodipodi:role="line"
+         id="tspan4522-6"
+         x="103.18751"
+         y="66.100143"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:4.23333311px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332" /></text>
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;line-height:4px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';text-align:center;letter-spacing:0px;word-spacing:0px;text-anchor:middle;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="96.572922"
+       y="254.66664"
+       id="text4524-6-0-4-2-1-02-1-0-8-2-0-69-7-9-2"><tspan
+         sodipodi:role="line"
+         x="96.572922"
+         y="257.75211"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;line-height:4px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';text-align:center;text-anchor:middle;stroke-width:0.26458332"
+         id="tspan2059-6-3-70" /></text>
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="63.715191"
+       y="268.32797"
+       id="text2086"><tspan
+         sodipodi:role="line"
+         id="tspan2084"
+         x="63.715191"
+         y="268.32797"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332">core0</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#000000;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2088"
+       width="13.229166"
+       height="13.229166"
+       x="61.515621"
+       y="260.61978" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#bfbfbf;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="80.913109"
+       y="268.32797"
+       id="text2086-3"><tspan
+         sodipodi:role="line"
+         id="tspan2084-0"
+         x="80.913109"
+         y="268.32797"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';fill:#bfbfbf;stroke-width:0.26458332">core1</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#bfbfbf;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2088-2"
+       width="13.229167"
+       height="13.229167"
+       x="78.713539"
+       y="260.61978" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#bfbfbf;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="63.715191"
+       y="284.20297"
+       id="text2086-0"><tspan
+         sodipodi:role="line"
+         id="tspan2084-9"
+         x="63.715191"
+         y="284.20297"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';fill:#bfbfbf;stroke-width:0.26458332">core2</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#bfbfbf;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2088-4"
+       width="13.229167"
+       height="13.229167"
+       x="61.515621"
+       y="276.49478" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#bfbfbf;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="80.913109"
+       y="284.20297"
+       id="text2086-9"><tspan
+         sodipodi:role="line"
+         id="tspan2084-3"
+         x="80.913109"
+         y="284.20297"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';fill:#bfbfbf;stroke-width:0.26458332">core3</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#bfbfbf;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2088-8"
+       width="13.229167"
+       height="13.229167"
+       x="78.713539"
+       y="276.49478" />
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#000000;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2131"
+       width="50.270832"
+       height="38.364582"
+       x="58.869789"
+       y="254.00519" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="96.13018"
+       y="276.37131"
+       id="text2086-37"><tspan
+         sodipodi:role="line"
+         id="tspan2084-1"
+         x="96.13018"
+         y="276.37131"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332">Cache</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#000000;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2151"
+       width="11.90625"
+       height="29.104166"
+       x="94.588539"
+       y="260.61978" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.26458332px;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1;marker-start:url(#Arrow2Lstart);marker-end:url(#Arrow2Lend)"
+       d="M 75.273958,271.2031 H 94.059374"
+       id="path2153"
+       inkscape:connector-curvature="0"
+       sodipodi:nodetypes="cc" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="81.359375"
+       y="257.97394"
+       id="text2086-7"><tspan
+         sodipodi:role="line"
+         x="81.359375"
+         y="257.97394"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332"
+         id="tspan2681">CPU</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#000000;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2685"
+       width="15.874998"
+       height="38.36459"
+       x="122.36979"
+       y="254.00519" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="126.7407"
+       y="274.2811"
+       id="text2086-37-1"><tspan
+         sodipodi:role="line"
+         id="tspan2084-1-8"
+         x="126.7407"
+         y="274.2811"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332">DRAM</tspan></text>
+    <rect
+       style="fill:#000000;fill-opacity:0;stroke:#000000;stroke-width:0.26458332;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2685-4"
+       width="19.843758"
+       height="38.364578"
+       x="151.47395"
+       y="254.00519" />
+    <text
+       xml:space="preserve"
+       style="font-style:normal;font-weight:normal;font-size:10.58333302px;line-height:1.25;font-family:sans-serif;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.26458332"
+       x="153.51477"
+       y="274.39047"
+       id="text2086-37-1-3"><tspan
+         sodipodi:role="line"
+         id="tspan2084-1-8-2"
+         x="153.51477"
+         y="274.39047"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:3.52777767px;font-family:'Ubuntu Mono';-inkscape-font-specification:'Ubuntu Mono';stroke-width:0.26458332">Videocore</tspan></text>
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.26458332px;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1;marker-start:url(#Arrow2Lstart-5);marker-end:url(#Arrow2Lend-6)"
+       d="m 107.02396,273.18748 h 14.81667"
+       id="path2153-1"
+       inkscape:connector-curvature="0"
+       sodipodi:nodetypes="cc" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.26458332px;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1;marker-start:url(#Arrow2Lstart-5-5);marker-end:url(#Arrow2Lend-6-6)"
+       d="m 138.77396,273.18747 h 12.17083"
+       id="path2153-1-2"
+       inkscape:connector-curvature="0"
+       sodipodi:nodetypes="cc" />
+  </g>
+</svg>