FPGA computer boots from the SD card

FPGA computer boots now from the SD card

This is a follow-up of my first text about 32-bit FPGA computer.

The 32-bit FPGA computer now has a kind of a hard disk. ESP32 is used as a hard disk controller (I have designed the board to work with the Arduino as well - you can see the empty socket for the Arduino to the right of the ESP32), while the SD card is used as a kind of a hard disk.

The FPGA computer with the ESP32-Arduino board is on the images above and below.

Initially, it was just the Arduino:

Since the FPGA computer is designed to boot from the serial port, I have created a kind of a hard disk controller, which consists of an ESP32 and SD card reader. When started, ESP32 lists files in the root folder of the SD card, and if it finds the file "BOOT.BIN", it reads it and sends the content to the FPGA computer over the serial port, using the Raspbootin protocol (as described in one of my previous posts).

The video above shows the boot from the powerup. Next video shows boot from the reset.

The code is available at the github.

This is the schematics:

The main idea is that the controller behaves just like the PC from which the FPGA computer initally gets its boot code. During the powerup, the FPGA computer will try to load the boot code from the serial interface, using a modified Raspbootin protocol. On the other side of the serial cable, there can be a PC with the corresponding Raspbootin client, or, just like in this case, the microcontroller, which has the following functionality:

1. wait for the Raspbootin start sequence,
2. look for the BOOT.BIN file in the SD card, and
3. send that file content over serial cable, using the Raspbootin protocol.

The FPGA computer would then boot from the loaded BOOT.BIN file. The BOOT.BIN file is the assembled file obtained using the custom assembler also available on my github page.

Conclusion

With this board, the FPGA-based computer can now boot from the SD card. Next step would be to extend the code so it would be used as a real SD controller, allowing the FPGA computer to open files, read, write, delete, etc.

ENC28J60 with 12-pin connector

I have recently purchased this module, and it has some strange pin names:

As you can see, some pins have wrong names:
LNT is actually INT
ST is actually SI (MOSI)
Q3 is actually 3.3V power
SCK is sometimes referred to SCLK (don't use the CLK for the SPI clock)

I am posting this to help people who, just like me, purchased this strange module.

Two-way AC control

How to control the AC two way using Raspberry Pi

In my previous posts, I have described my small Home Automation system. It consists of various sensors, connected to several Raspberry Pi computers. The control was initially one-way, meaning that I could only watch sensor data on the Home Automation web site. Then I have added AC remote control support to the system. I have used the lirc library which enables user to record IR commands and then to reproduce them. The initial setup enabled users to remotely control the AC from the Home web site. However, there was no way of knowing the actual AC status (if the AC already works or not). This means that the Home web site could not display the current AC status and instead of turning the AC on, we could turn it off. That is the topic of this post - how to add the support to the Home Automation system, which can read AC status.

By default, the AC is controlled using the IR remote. I have rather old AC, which is not connected to the WiFi, so there is only one way of knowing if the AC is working or not - the status LED at the AC device. I have figured out a way to read the LED status and to feed that information to the RPI. The Idea is quite simple: glue the photo sensitive resistor to the AC status LED, and connect that resistor to the simple circuit which gives an information to the RPI if the AC is working.

This is the photo sensitive resistor - photoresistor:

Here is the circuit:

The photo resistor decreases the resistance when exposed to the light. If there is no light, the resistance is couple of hundred kilo Ohms. When lit by the AC LED, the resistance drops to the approx. 20 kilo Ohms. Since the circuit is actually a voltage divider, when LED is not lit, the voltage at the GPIO port is high, meaning logical 1. If the LED is turned on, the resistance drops, the voltage at the divider drops, and the GPIO port reads 0.

The Python code which reacts to the change of LED operation is here:

PORT_AC = 21
GPIO.setmode(GPIO.BCM)
GPIO.setup(PORT_AC, GPIO.IN)

acStatus = not GPIO.input(PORT_AC)
print 'AC STATUS: ', acStatus

def ac_edge_detected(channel):
  time.sleep(0.25) // give some time to properly read GPIO port
  print 'AC EDGE detected, channel is ', channel
  global acStatus
  acStatus = not GPIO.input(PORT_AC)
  print 'AC STATUS: ', acStatus
  requests.get('http://' + STATUS_HOST + ':8080/setAc/' + str(acStatus))

GPIO.add_event_detect(PORT_AC, GPIO.BOTH, callback=ac_edge_detected, bouncetime=50)

Here is how it looks implemented:

And here is the AC part of the Home Web application:

Conclusion

Initial AC solution provided me with the option of turning on/off AC remotely. However, the system could not know the initial and current AC status, making turning on/off unreliable. This contraption is capable of determining the AC status by observing the AC LED status. It does so by having the voltage over the photo resistor dropping when the LED is turned on.