846 Cynergy4MIE SPI Slave Component :: Quicker, easier and cheaper to make your own chip!

How it works

This projects consists of an SPI slave and other components. The SPI slave accepts an 8-bit address and an 8-bit data value. Write transactions always have bit 7 of the address set. Write transactions always have bit 7 of the address cleared. There should be a pause between address and data transactions of at least 3 system clock cycles. The project includes a register map of 21 registers, GPIO module, LFSR with serial output, timer module with PWM and capture on rising and falling edges.

Example:

Read transaction. Read data from timer capture register 1.

|00001111|pause|11101001|
 address          data

Write transaction. Enable PWM and start the timer.

|10000001|pause|00000101|
 address          data

How to test

Simulation

This project uses cocotb and Icarus Verilog. Even though it is a VHDL project, it was transpiled using GHDL, so you can use Verilog simulation tools. Just run make in the test directory.

Register map

Address	Description
0x00	Timer control
0x01	Timer top
0x02	Timer clock divisor
0x03	Timer capture control
0x04	GPIO read data
0x05	GPIO write data
0x06	GPIO direction
0x07	LFSR polynome
0x08	LFSR control
0x09	LFSR state input
0x0a	PWM 0 top
0x0b	PWM 1 top
0x0c	PWM 2 top
0x0d	PWM 3 top
0x0e	Capture 0 register
0x0f	Capture 1 register
0x10	Capture 2 register
0x11	Capture 3 register
0x12	Capture 4 register
0x13	Capture 5 register
0x14	Capture 6 register
0x15	Capture 7 register

Description of each register

All registers are 0 after reset by default.

Timer control (0x00)

You can enable or disable features of the timer through this register.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Unused	Unused	Unused	Timer overflow control	Capture control	PWM control	Direction control	Timer enable
--------	--------	--------	-------------------------	-----------------------	-------------------	-------------------	---------------------
			'1' - reset on top	'1' - enable capture	'1' - enable PWM	'1' - count down	'1' - enable timer
			'0' - reset on overflow	'0' - disable capture	'0' - disable PWM	'0' - count up	'0' - disable timer

Timer top (0x01)

Timer top value. If bit 4 of the timer control register is set, then timer will count up to this value and roll back to 0.

Timer clock divisor (0x02)

Divides the clock of the timer by (value + 1). By default it is 0, so divisor is 1.

Timer capture control (0x03)

Controls the edges at which the time of events will be saved

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Capture 7 edge	Capture 6 edge	Capture 5 edge	Capture 4 edge	Capture 3 edge	Capture 2 edge	Capture 1 edge	Capture 0 edge
--------------------	--------------------	--------------------	--------------------	--------------------	--------------------	--------------------	--------------------
'1' - rising edge	'1' - rising edge	'1' - rising edge	'1' - rising edge	'1' - rising edge	'1' - rising edge	'1' - rising edge	'1' - rising edge
'0' - falling edge	'0' - falling edge	'0' - falling edge	'0' - falling edge	'0' - falling edge	'0' - falling edge	'0' - falling edge	'0' - falling edge

GPIO read data (0x04)

GPIO input register.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Unused	Unused	Unused	Unused	GPIO pin 3	GPIO pin 2	GPIO pin 1	GPIO pin 0
--------	--------	--------	--------	----------------	----------------	----------------	----------------
				'1' - pin high	'1' - pin high	'1' - pin high	'1' - pin high
				'0' - pin low	'0' - pin low	'0' - pin low	'0' - pin low

GPIO write data (0x05)

GPIO output register.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Unused	Unused	Unused	Unused	GPIO pin 3	GPIO pin 2	GPIO pin 1	GPIO pin 0
--------	--------	--------	--------	----------------	----------------	----------------	----------------
				'1' - set high	'1' - set high	'1' - set high	'1' - set high
				'0' - set low	'0' - set low	'0' - set low	'0' - set low

GPIO direction (0x06)

GPIO direction register. GPIO is connected to uio port of the Tiny Tapeout IC. By default all pins are inputs.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Unused	Unused	Unused	Unused	GPIO pin 3	GPIO pin 2	GPIO pin 1	GPIO pin 0
--------	--------	--------	--------	--------------	---------------	----------------	----------------
				'1' - output	'1' - output	'1' - output	'1' - output
				'0' - input	'0' - input	'0' - input	'0' - input

LFSR polynome (0x07)

LFSR polynome register. Max L polynome for an 8 bit LFSR is 0x63.

LFSR control (0x08)

This register controls the LFSR.

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
Unused	Unused	Unused	Unused	Unused	Unused	Load enable	LFSR enable
--------	--------	--------	--------	--------	--------	-------------------------------	--------------------
						'1' - load inital value	'1' - enable LFSR
						'0' - don't load inital value	'0' - disable LFSR

LFSR state input (0x09)

You can set the initial state through this register.

PWM tops (0x0a -- 0x0d)

You can set tops for the PWM or use these as general purpose registers.

Capture registers (0x0e -- 0x15)

These registers hold the time of event edges happened at capture pins.

How to use

How to use the Timer.

Starting the timer
1. Set the clock divisor through the register 0x02 (optional).
2. Set the top value through the register 0x01 (optional).
3. Configure bits 4 and 1 of the register 0x00 as you wish.
4. Start the timer by setting bit 0 of the register 0x00.
Using PWM
1. Set PWM tops (registers 0x0a -- 0x0d).
2. Set bit 2 of the register 0x00
3. Start the timer.
Using event capturing
1. Set bit 3 of the register 0x00
2. Configure capture edges in the register 0x03
3. Read captured times from registers 0x0e -- 0x15

How to use the GPIO.

Configure the register 0x06 as you wish.
Use register 0x05 to set digital output.
Use register 0x05 to read digital input.

How to use the LFSR.

Load the initial value into register 0x09.
Load the polynome into register 0x09 (I suggest 0x63, because it is a max L polynome).
Set set bits 0 and 1 of the register 0x08 (enable the LFSR and enable loading).
Clear bit 1 of the register 0x08 (disable loading).
The LFSR will how cycle through all states resulting from the loaded polynome.

External hardware

The pins of the SPI slave are assigned so that you could use PMOD SPI master. Any other USB-to-SPI master should suffice. You can also use LEDs and buttons for GPIO.

#	Input	Output	Bidirectional
0	Capture 0	CS	PWM 0
1	Capture 1	MOSI	PWM 1
2	Capture 2	MISO	PWM 2
3	Capture 3	SCK	PWM 3
4	Capture 4	GPIO 0	LFSR
5	Capture 5	GPIO 1	NC
6	Capture 6	GPIO 2	NC
7	Capture 7	GPIO 3	NC

846 Cynergy4MIE SPI Slave Component