Add test board documentation (#3359)

Author: pjsg

tests/HardwareTestHarness.md

@@ -0,0 +1,181 @@
+Hardware Test Harness
+=====================
+
+There is an implementation of the hardware testing design which is a small 4in x 4in board with positions for
+two Wemos D! Mini ESP8266 boards, a breadboard area and a number of positions for peripherals. The schematics
+are in [schematic](Test-harness-schematic-v1.pdf) and a rendering of the board is ![Board Render](Test-Harness-Render-V1.png). 
+
+
+The test harness runs from a dedicated host computer, which is expected
+to have reset- and programming-capable UART links to both ESP8266
+devices, as found on almost all ESP8266 boards with USB to UART
+adapters, but the host does not necessarily need to use USB to connect,
+so long as TXD, RXD, DTR, and RTS are wired across.
+
+The alternate pins on the primary D1 Mini (DUT0) are cross wired to the
+RX and TX pins on the secondary D1 Mini (DUT1) and these are enabled by
+a pin on the MCP23017.
+
+Build Notes
+-----------
+
+The only thing that needs to be done is to solder on 0.1" headers at the required
+positions. Typically D1 Minis come with 2 sets of 8 pin headers, both male and female.
+I solder the female headers to the board, and the maie headers to the D1 minis. Other,
+mostly 4 pin, headers can be soldered at the other positions. The 7 pin header for
+the color sensor (TCS34725) requires some care as the board needs to be mounted
+upside down so that the sensor is directly above the WS2812. 
+
+The screw holes at the corners are for M3 screws. A standard adhesive rubber foot can
+also be used. There are no components on the underside of the test board, so not much clearance
+is required (only the length of the various headers soldered on the board).
+
+Power
+-----
+
+The board is powered by either (or both) D1 Mini USB connection. Given the cross connects
+between the two D1 Minis, I think that all the tests can be conducted from DUT0, but
+it is probably easier to connected both of the D1 Minis via USB to the test runner.
+
+There is a small resistor between the two 5 volt rails to prevent large currents
+if the two USB feeds are at slughtly different voltages. The 3.3 volt rails are
+directly connected together. If the regulators produce slightly different voltages,
+then the one producing the higher voltage will end up providing all the power for the
+3.3 volt devices.
+
+Peripherals
+-----------
+
+### I2C Bus
+
+There is an I2C bus hanging off DUT 0. Attached hardware is used both as
+tests of modules directly and also to facilitate testing other modules
+(e.g., gpio).
+
+Most of the positions on the board are connected to the DUT1 I2C bus.
+
+#### MCP23017: I/O Expander
+
+At address 0x20. An 16-bit tristate GPIO expander, this chip is used to
+test I2C, GPIO, and ADC functionality. This chip's interconnections are
+as follows:
+
+MPC23017 | Purpose
+---------|--------------------------------------------------------------
+/RESET   |DUT0 reset. This resets the chip whenever the host computer resets DUT 0 over its serial link (using DTR/RTS).
+B 0      |4K7 resistor to DUT 0 ADC.
+B 1      |2K2 resistor to DUT 0 ADC.
+B 2      |Direct to DUT1 RST
+B 3      |Direct to DUT1 D3
+B 4      |When low, connects the alternate UART pins on DUT0 to RX,TX on DUT1
+B 5      |DUT1 GPIO16/WAKE via 4K7 resitor
+B 6      |DUT0 GPIO13 via 4K4 resistor and DUT1 GPIO15 via 4K7 resistor (also feeds in the primary TX from DUT1 when enabled by B4)
+B 7      |DUT0 GPIO15 via 4K7 resistor and DUT1 GPIO13 via 4K7 resistor (also feeds the primary RX on DUT1 when enabled by B4)
+
+Notes:
+
+-   DUT 0's ADC pin is connected via a 2K2 reistor to this chip's port
+    B, pin 1 and via a 4K7 resistor to port B, pin 0. This gives us the
+    ability to produce approximately 0 (both pins low), 1.1 (pin 0 high,
+    pin 1 low), 2.2 (pin 1 high, pin 0 low), and 3.3V (both pins high)
+    on the ADC pin.
+-   Port B pins 6 and 7 sit on the UART cross-wiring between DUT 0 and
+    DUT 1. The 23017 will be tristated for inter-DUT UART tests, but
+    these
+-   All of port A, remain available for expansion and are routed to the breadboard area.
+
+#### WS2812s
+
+There are three WS2812s connected on DUT1/D4. The last Ws2812 is positioned so that a TCS34725 module
+can be mounted upside down over it to read out the color of the WS2812. That device is connected to
+the I2C port on DUT0. A suitable board is [CJMCU-34725 TCS34725 Color Sensor RGB color sensor development board module](https://www.aliexpress.com/item/32412698433.html). The illuminating
+LED is connected to the INT pin and so you can disable the LED under software control.
+
+#### Oled Displays
+
+Each of the D1 Minis is connected to a position for a 128x64 OLED display, again on the primary I2C bus.    
+
+#### Servo
+
+On DUT1 pin D4/GPIO 2 there is a connection to a position for a small servo. The servo is powered by the
+5V voltage rail. 
+
+#### DHTxx
+
+On DUT1 pin D6/GPIO 12 there is a connection to a position for a DHTxx device. The silk screen indicates the
+orientation of the device.
+
+#### DS18B20
+
+There are two positions for DS18B20s -- one with the VCC pin connected and one without. The data pin is
+connected to DUT1 pin D5/GPIO 14.
+
+#### I2C devices with VCC/GND/SCL/SDA pin order
+
+There are three positions for I2C devices which have the pins in the VCC/GND/SCL/SDA order. These
+are on the DUT1 I2 bus.
+
+#### I2C devices with other pin orders
+
+There are three positions for I2C devices with other pin orders. Each of these positions is next
+to a crossbar switch and so four blobs of solder can configure each of these headers into any
+desired pin order. As far as I can tell, most of the cheap modules use the VCC/GND/SCL/SDA order.
+
+
+Breadboard Area
+===============
+
+All the pins on each D1 Mini and the A port of the MCP23017 are brought out to a breadboard 
+area. This can be used to solder components and/or wires, or even a header could be soldered
+on to transfer all the signals to a conventional breadboard. 
+
+
+ESP8266 Device 0 Connections
+----------------------------
+
+ESP       | Usage
+----------|----------------------------------------------------------
+D3/GPIO 0    |Used to enter programming mode; otherwise unused in test environment.
+TX/GPIO 1    |Primary UART transmit; reserved for host communication
+D4/GPIO 2    |[reserved for 1-Wire] [+ reserved for 23017 INT[AB] connections]
+RX/GPIO 3    |Primary UART recieve; reserved for host communication
+D2/GPIO 4    |I2C SDA. Connected to MCP23017, Oled display and the TCS34725 if present. 
+D1/GPIO 5    |I2C SCL
+GPIO 6    |[Reserved for on-chip flash]
+GPIO 7    |[Reserved for on-chip flash]
+GPIO 8    |[Reserved for on-chip flash]
+GPIO 9    |[Reserved for on-chip flash]
+GPIO 10   |[Reserved for on-chip flash]
+GPIO 11   |[Reserved for on-chip flash]
+D6/GPIO 12   |
+D7/GPIO 13   |Secondary UART RX; DUT 1 GPIO 15, I/O expander B 6
+D5/GPIO 14   |
+D8/GPIO 15   |Secondary UART TX; DUT 1 GPIO 13, I/O expander B 7
+D0/GPIO 16   |
+A0/ADC 0     |Resistor divider with I/O expander
+
+ESP8266 Device 1 Connections
+----------------------------
+
+ESP       | Usage
+----------|----------------------------------------------------------
+D3/GPIO 0    |Used to enter programming mode; otherwise unused in test environment.
+TX/GPIO 1    |Primary UART transmit; reserved for host communication
+D4/GPIO 2    |Connected to chain of 3 WS2812s. Also connected to the servo position.
+RX/GPIO 3    |Primary UART recieve; reserved for host communication
+D2/GPIO 4    |I2C SDA. Connected to all the other I2C positions on the board
+D1/GPIO 5    |I2C SCL
+GPIO 6    |[Reserved for on-chip flash]
+GPIO 7    |[Reserved for on-chip flash]
+GPIO 8    |[Reserved for on-chip flash]
+GPIO 9    |[Reserved for on-chip flash]
+GPIO 10   |[Reserved for on-chip flash]
+GPIO 11   |[Reserved for on-chip flash]
+D6/GPIO 12   |Connected to data pin for DHTxx
+D7/GPIO 13   |Secondary UART RX; DUT 0 GPIO 15, I/O exp B 7 via 4K7 Also used as HSPI MOSI for SPI tests
+D5/GPIO 14   |Connected to data pin for DS18B20s.
+D8/GPIO 15   |Secondary UART TX; DUT 0 GPIO 13, I/O exp B 6 via 4K7 Also used as HSPI /CS for SPI tests
+D0/GPIO 16   |I/O expander B 5 via 4K7 resistor, for deep-sleep tests
+A0/ADC 0     |
+
+

tests/README.md

@@ -124,6 +124,8 @@ devices, as found on almost all ESP8266 boards with USB to UART
 adapters, but the host does not necessarily need to use USB to connect,
 so long as TXD, RXD, DTR, and RTS are wired across.
 
+A particular implementation of this can be found at [Test Harness](HardwareTestHarness.html).
+
 ## Peripherals
 
 ### I2C Bus