1.. _docs-blog-01-kudzu: 2 3========================== 4Pigweed Eng Blog #1: Kudzu 5========================== 6.. raw:: html 7 8 <script type="application/ld+json"> 9 { 10 "@context": "https://schema.org", 11 "@type": "NewsArticle", 12 "headline": "Kudzu: Pigweed's whimsical take on a development board", 13 "image": [ 14 "https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-diagonal.jpg" 15 ], 16 "datePublished": "2023-10-12T19:27:00+08:00", 17 "dateModified": "2023-10-12T19:27:00+08:00", 18 "author": [{ 19 "@type": "Person", 20 "name": "Erik Gilling", 21 "url": "https://github.com/konkers" 22 }] 23 } 24 </script> 25 26.. admonition:: A note from the Pigweed Eng Blog editors 27 28 Welcome to the Pigweed Eng Blog! This is an informal blog where Pigweed 29 teammates, contributors, and users can share ideas and projects related to 30 Pigweed. 31 32 Our first post comes from Erik Gilling, a software engineer on the 33 Pigweed team. Today, Erik is going to tell you about Kudzu, 34 "Pigweed's whimsical take on a development board"… 35 36 Please note that **while Kudzu is open source, its hardware isn't publicly 37 available**. Pigweed users may find the `Kudzu source 38 code <https://pigweed.googlesource.com/pigweed/kudzu/+/refs/heads/main>`_ 39 to be a helpful example of a complex Pigweed integration. 40 41.. card:: 42 :img-background: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-diagonal.jpg 43 :link: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-diagonal.jpg 44 :img-alt: A single Kudzu badge face-up on a table viewed at a diagonal. 45 46---------------------------- 47It all started so innocently 48---------------------------- 49The Pigweed team is taking a field trip to the 50`Bay Area Maker Faire <https://makerfaire.com/bay-area/>`_ because 51unsurprisingly, that's the kind of good time we're up for! While discussing 52the plans at a team meeting I suggested: "We should make PCB badges that run 53Pigweed and wear that to the Faire!" I've always wanted to make a PCB badge 54and this seemed like the perfect opportunity to make a simple PCB that we could 55do a little bit of hacking on. 56 57-------- 58"Simple" 59-------- 60The idea resonated with the team… perhaps too well. What started as 61something simple in my head quickly started creeping features. Hence 62the name `Kudzu <https://en.wikipedia.org/wiki/Kudzu>`_: a vine 63considered invasive in many parts of the world. Pigweed's a weed. 64Our RFCs are called "seeds". We're all about the plant puns… 65 66Anyways, the conversation went something like this: 67 68 "We should have some sort of sensor so it does something…" 69 70 "How should we power it? Let's do LiPo charging…" 71 72 "Let's add a display to highlight our recent 73 :ref:`Display Support SEED <seed-0104>`!" 74 75 "Touch screen?" 76 77 "D-Pad and buttons?" 78 79 "Speaker?" 80 81 "Wireless?" 82 83 "No!… but also yes…" 84 85We quickly realized that what we wanted was more than a badge. We wanted a 86showcase for Pigweed. We wanted a project we can point people at to show them 87Pigweed running at it's best. And thus Kudzu was born. Part badge, part 88development board, part handheld gaming system, and all Pigweed. 89 90---------------- 91The laundry list 92---------------- 93We settled on the following laundry list of features and components: 94 95`RP2040 Microcontroller <https://www.raspberrypi.com/documentation/microcontrollers/rp2040.html>`_ 96 There's a lot to love about the RP2040: a reasonable amount of SRAM, 97 support for large/cheap/execute-in-place external flash, a wicked cool 98 programmable I/O block, and most importantly: easy and cheap to source! 99 100`16 MB of Flash <https://www.winbond.com/resource-files/w25q128jv%20revf%2003272018%20plus.pdf>`_ 101 We're adding the maximum amount of flash that the RP2040 can support. This 102 way we can pack as much awesome into the firmware as possible. Realistically 103 16 MB is an embarrassingly large amount of space for an embedded project and I 104 can't wait to see what cool stuff we fill it with! 105 106USB-C Connector 107 While we're not adding USB Power Delivery to the board, the USB C connector 108 is robust and common. Many of us on the team are tired of digging micro 109 (or even mini) USB cables out of our desk drawers to hook up brand new dev 110 boards or JTAG programmers! 111 112LiPo Battery with `charger <https://www.microchip.com/en-us/product/mcp73831>`_ and `fuel gauge <https://www.analog.com/en/products/max17048.html>`_ 113 Once we decided on a portable gaming form factor, we wanted to have a 114 built-in, rechargeable battery. The battery is 900mA and is set to charge at 500mA 115 from USB when the system is off and 250mA when the system is running. As an 116 added bonus we threw in a fuel gauge chip. Partly because it's really nice to 117 have an accurate view of the battery charge state and partly because it's 118 a neat chip to write software for. 119 120`3.2" IPS display with capacitive touch <https://www.buydisplay.com/3-2-inch-240x320-ips-tft-lcd-display-optl-capacitive-touchscreen-st7789>`_ 121 This display is 240x320 which presents two challenges. First, it's naturally 122 portrait instead of landscape. We solve this by rotating the buffers once 123 they're rendered. The second is that a single 16-bit x 320 x 240 frame buffer 124 is ~150K which is over half of the 264K of SRAM in the RP2040. Instead, we're 125 rendering at 160x120 and using the PIO module to `pixel double 126 <https://github.com/32blit/32blit-sdk>`_ the buffer as we're sending it to the 127 display. As an added bonus, the chunkier pixels gives Kudzu a nice retro feel. 128 129Directional Pad and Buttons 130 Here we're leaning on off-the-shelf buttons and silicone pads. Game 131 controller design is a whole rabbit hole and we're going to rely on the 132 collective wisdom of the retro modding community to give us nice-feeling 133 controls. 134 135`Six Axis IMU <https://invensense.tdk.com/products/motion-tracking/6-axis/icm-42670-p/>`_ 136 An IMU is a great general purpose peripheral to demonstrate Pigweed's HAL 137 layer. Plus, there's all sorts of cool demos you can write with an IMU and 138 a display. 139 140`I2S Audio DAC/Amplifier <https://www.analog.com/media/en/technical-documentation/data-sheets/max98357a-max98357b.pdf>`_ and Speaker 141 Chip tunes are best tunes. A couple of us on the team would love to 142 port/write a tracker or FM synthesis engine. 143 144Gameboy Advance Link Port 145 As a simple way of hooking two devices together, we added link port. Again 146 we're using an existing link port and cable to avoid reinventing to wheel. 147 Plus, there's something awful nostalgic about that port! 148 149... and `One More Thing <https://www.espressif.com/en/products/socs/esp32-c3>`_ 150 I kinda snuck an ESP32-C3 module onto the board at the last minute. Having 151 wireless is something we wanted but didn't want to burden the initial design 152 and bring up with it. My thinking is that we'll leave the module un-populated 153 for now. My hope is that adding it to the board now may keep these boards from 154 becoming landfill when we decide to tackle wireless. 155 156-------------------------- 157Design, build, and rollout 158-------------------------- 159I used `KiCad <https://www.kicad.org/>`_ to design the board. It's an open 160source PCB design package that has been making incredible strides in 161functionality and usability in the past few years. It comes with a high-quality 162library of symbols and footprint which is supplemented by community-maintained 163open source libraries. 164 165.. card:: 166 :img-top: https://storage.googleapis.com/pigweed-media/kudzu-schematic.png 167 :link: https://storage.googleapis.com/pigweed-media/kudzu-schematic.png 168 :img-alt: A screenshot of Kudzu's schematic. 169 :text-align: center 170 171 Kudzu schematic 172 173After some careful design review from the team and a few friends of Pigweed we 174sent off the board to get fabbed and "patiently" waited for it to be delivered. 175 176An EE at a previous company I worked at had a saying: "If you haven't found 177three problems with your board, you're not done looking". The three problems 178we found in order from least to most crushing are: 179 180.. card:: 181 :img-top: https://storage.googleapis.com/pigweed-media/kudzu-display-connector.jpeg 182 :link: https://storage.googleapis.com/pigweed-media/kudzu-display-connector.jpeg 183 :img-alt: The reworked display connector with many bodge wires. 184 :text-align: center 185 186 The reworked display connector and the unpopulated footprint for the "one more thing" 187 that "we'll get to eventually" 188 189#. **The BOOT and RESET labels were reversed.** This led to some initial 190 confusion on why the boards would not come up in bootloader mode. 191 192#. **One of the FETs (Q3) had the wrong pinout.** This caused the power 193 switch to be stuck on and the charge rate switching to not work. 194 195#. **The pins on the display FPC connector were swapped.** This one was really 196 crushing. The connector was fairly fine-pitched and 40 pins! 197 198We were able to bring up the whole board including the display by rotating the 199connector. Sadly the display would not fit in the 3D printed parts 200we'd designed when plugged into the rotated connection. To validate our 3D 201printed parts, I painstakingly reworked on-board to get the connector oriented 202correctly. However, that was too much work and too fragile for all the boards. 203We had to do a re-spin and Maker Faire was approaching quickly! Time to lather, 204rinse, and repeat. 205 206Fast forward to Monday night before Maker Faire. The boards come in and I spent 207the evening preparing for a build party. On Tuesday, with some 208`robotic help <https://www.opulo.io/>`_, we managed to build and test 8 boards 209and get them in team members' hands on Wednesday. 210 211.. card:: 212 :img-top: https://storage.googleapis.com/pigweed-media/kudzu-pnp.jpg 213 :link: https://storage.googleapis.com/pigweed-media/kudzu-pnp.jpg 214 :img-alt: A photo of the Opulo LumenPnP 215 :text-align: center 216 217 Our robotic help (Opulo LumenPnP) 218 219Thankfully, because Pigweed is modular and portable, we were able to get our 220software working on it quickly, freeing us to spend the next couple days hacking 221together some simple fun demos for Maker Faire! 222 223------ 224Photos 225------ 226.. grid:: 1 1 2 2 227 228 .. grid-item-card:: 229 :img-background: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-diagonal.jpg 230 :link: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-diagonal.jpg 231 :img-alt: A single Kudzu badge face-up on a table viewed at a diagonal. 232 233 .. grid-item-card:: 234 :img-background: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-back.jpg 235 :link: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-back.jpg 236 :img-alt: A single Kudzu badge face-down on a table viewed at a diagonal. 237 238.. grid:: 1 1 2 2 239 240 .. grid-item-card:: 241 :img-background: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-top-down.jpg 242 :link: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-top-down.jpg 243 :img-alt: A single Kudzu badge face-up on a table viewed from above. 244 245 .. grid-item-card:: 246 :img-background: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-front-standing.jpg 247 :link: https://storage.googleapis.com/pigweed-media/kudzu-finished-photo-front-standing.jpg 248 :img-alt: A single Kudzu badge standing up on a table viewed from the front. 249 250.. card:: 251 :img-top: https://storage.googleapis.com/pigweed-media/kudzu-badges.jpg 252 :link: https://storage.googleapis.com/pigweed-media/kudzu-badges.jpg 253 :img-alt: A photo of 6 of the Kudzu badges 254 :text-align: center 255 256 Six Kudzu badges for Maker Faire 2023 257 258---------- 259Learn more 260---------- 261We don't have any plans to distribute hardware outside of our team but are 262excited to publish the living project to serve as an example of how to build 263firmware integrated with Pigweed. Over the coming months we'll be publishing 264more functionality to the repository. 265 266Head over to the `Kudzu repo <https://pigweed.googlesource.com/pigweed/kudzu>`_ 267where you'll find: 268 269* KiCad PCB Design 270* Example firmware demonstrating: 271 * :ref:`module-pw_system` integration 272 * :ref:`module-pw_rpc` and :ref:`module-pw_log` support 273 * Use of Pigweed's :ref:`module-pw_digital_io`, :ref:`module-pw_i2c`, 274 and :ref:`module-pw_spi` hardware abstraction layers 275 276.. pigweed-live:: 277
