Make pin chart accessible, add toolchain note

1 files changed, 11 insertions, 1 deletions

diff --git a/README.md b/README.md
index c13103e1..2c9a6db1 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,15 @@ You may have noticed that there are no sensors on this board. That is by design:
     * Up to four PWM pins on two independent TC instances
     * Two external wake inputs that can wake from the ultra-low-power BACKUP mode
 
-![image](/images/sensor-board-pinout.png)
+| **Pin** | **Digital** | **Interrupt**   | **Analog**    | **I2C**             | **SPI**              | **UART**                 | **PWM**  | **Ext. Wake** |
+| :-----: | :---------: | :-------------: | :-----------: | :-----------------: | :------------------: | :----------------------: | :------: | :-----------: |
+| **A4**  | PB00        | EIC/EXTINT\[0\] | ADC/AIN\[8\]  | —                   | MISO<br>SERCOM3\[2\] | TX or RX<br>SERCOM3\[2\] | TC3\[0\] | RTC/IN\[0\]   |
+| **A3**  | PB03        | EIC/EXTINT\[3\] | ADC/AIN\[11\] | —                   | CS<br>SERCOM3\[1\]   | RX<br>SERCOM3\[1\]       | TC2\[1\] | —             |
+| **A2**  | PB02        | EIC/EXTINT\[2\] | ADC/AIN\[10\] | —                   | MOSI<br>SERCOM3\[0\] | TX or RX<br>SERCOM3\[0\] | TC2\[0\] | RTC/IN\[1\]   |
+| **A1**  | PB01        | EIC/EXTINT\[1\] | ADC/AIN\[9\]  | —                   | SCK<br>SERCOM3\[3\]  | RX<br>SERCOM3\[3\]       | TC3\[1\] | —             |
+| **SDA** | —           | —               | —             | SDA<br>SERCOM1\[0\] | —                    | —                        | —        | —             |
+| **SCL** | —           | —               | —             | SCL<br>SERCOM1\[1\] | —                    | —                        | —        | —             |
+| **A0**  | PB04        | EIC/EXTINT\[4\] | ADC/AIN\[12\] | —                   | —                    | —                        | —        | —             |
 
 These tiny “sensor boards” have a set outline, and the available area for your electronics is quite small (5.7 × 5.7 × 1 mm). Still, this is plenty of room for an environmental sensor, MEMS accelerometer or magnetometer and a couple of decoupling capacitors. Note that you will likely be limited to QFN and LGA type parts; SOICs are too large, and even SSOP packages are generally too thick. You can find reference designs for several sensor boards in the `PCB/Sensor Boards` directory within this repository.
 
@@ -39,6 +47,8 @@ Getting code on the watch
 -------------------------
 The watch library in this repository is very work-in-progress, but it should allow you to get started. To create a new project, copy the “Sensor Watch Starter Project” and write your code in the app.c file.
 
+You will need to install [the 9-2019-q4-major version of the GNU Arm Embedded Toolchain](https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads/9-2019-q4-major) to build projects for the watch. Note that the latest version, 10-2020-q4-major, will not currently work.
+
 To build your project, open your terminal and navigate to the project's `make` folder, then type `make`.
 
 To install the project onto your Sensor Watch board, plug the watch into your USB port and double tap the tiny Reset button on the back of the board. You should see the LED light up red and begin pulsing. (If it does not, make sure you didn’t plug the board in upside down). Once you see the “WATCHBOOT” drive appear on your desktop, type `make install`. This will convert your compiled program to a UF2 file, and copy it over to the watch.