According to the pin placement requirements in Intel® Agilex™ General-Purpose I/O and LVDS SERDES User Guide, each x4 DQ group shares the same OE, reset, and clock enable signals, therefore you cannot split the OE, Reset or clock enable signals within a x4 DQ group. Given the constraint, here are some considerations when placing I2C pins.
1. FPGA is used as I2C master, requiring multi-master mode:
(i) A typical implementation of I2C is using OE on both SCL and SDA as shown below, thus you cannot place SCL and SDA in the same x4 DQ group.
assign i2c_serial_scl_in = arduino_adc_scl;
assign arduino_adc_scl = i2c_serial_scl_oe ? 1'b0 : 1'bz;
assign i2c_serial_sda_in = arduino_adc_sda;
assign arduino_adc_sda = i2c_serial_sda_oe ? 1'b0 : 1'bz;
(ii) Another way is to use GPIO Intel FPGA IP. You can enable open-drain for SCL and SDA, connect both OE ports for SCL and SDA to 1 (high), and connect the inverted signals of the original OE control signals. In this way, you can workaround the constraint. Following is an example:
gpioip gpioip_scl (
.dout (i2c_serial_scl_in),
.din (~i2c_serial_scl_oe),
.oe (1'b1),
.pad_io (arduino_adc_scl)
);
gpioip gpioip_sda (
.dout (i2c_serial_sda_in),
.din (~i2c_serial_sda_oe),
.oe (1'b1),
.pad_io (arduino_adc_sda)
);
2. FPGA is used a I2C master single mode:
SCL is an output pin without OE. SDA is a bidirectional pin with OE.
3. FPGA is used as I2C slave:
SCL is an input pin without OE. SDA is a bidirectional pin with OE.
In 2 and 3 above, because SCL doesn’t have OE,
- A SCL and a SDA can be assigned in the same x4 DQ group
- Multiple SCL and a SDA can be assigned in the same x4 DQ group
- Multiple SDA can’t be assigned in the same x4 DQ group
- When multiple SDA are assigned in the same x4 DQ group, using GPIO Intel FPGA IP as mentioned above is also a workaround.
