DE0-Nano and I2C Opencores Issues

Finally had a chance sit down and play around with DE0-Nano. I am using Quartus/Qsys 11.1 and Nios II 11.1 Software build tools.

I thought as a relatively quick project I would experiment using the opencores I2C master downloaded from alterawiki.com/wiki/I2C_(OpenCores) to interface with the ADXL345 accelerometer and 24LC02B eeprom ICs on the DE0-Nano board.

The first problem I hit was with the version of Qsys required by the I2C master (12.0 vs 11.1). I simply used the 'New component' wizard in Qsys to generate the new _hw.tcl file with the following wishbone to avalon bus signal assignments:

wb_clk_i --- clk

wb_rst_i --- reset

wb_adr_i --- address

wb_we_i --- write

wb_ack_o --- waitrequrest_n

wb_dat_i --- writedata

wb_dat_o --- readdata

wb_stb_i --- chipselect

wb_inta_o --- irq

scl_pad_io --- export

sda_pad_io --- export

I then made the following pin assignments

scl_pad_io == PIN F2 (output)

sda_pad_io == PIN F1 (bi-dir)

PIN G5 (G_SENSOR_CS_N) I tied to VCC to ensure the accelerometer is in I2C mode rather than SPI mode.

I had a few more niggles after this, specifically getting the driver to be recognised by Nios II IDE. Turns out I had to rename all instances of opencores_I2C to I2C_opencores in the _sw.tcl file.

Now I have the following code which is running on the DE0-Nano, which should write 0x55 to the first byte of the eeprom and read back the same byte as a second I2C transaction. The eeprom 7-bit address should be 0x50 (assuming I have found the correct datasheet). The software functions are defined with I2C_opencores available from the link above.

//Intialise I2C master controller at 100kHz, 50MHz Cpu clock.

I2C_init(I2C0_BASE,ALT_CPU_CPU_FREQ,100000);

// Write 0x55 to location 0x0 for I2C device at 0x50 (22LC02B)

I2C_start(I2C0_BASE,0x50,0);

I2C_write(I2C0_BASE,0x0,0);

I2C_write(I2C0_BASE,0x55,1);

// Write address that is to be read from

I2C_start(I2C0_BASE,0x50,0);

I2C_write(I2C0_BASE,0x0,0);

// Read from the device

I2C_start(I2C0_BASE,0x50,1);

data = I2C_read(I2C0_BASE,1);

printf("Data: 0x%x \n",data);

However I get the following console output if I defined I2C_DEBUG...

Initializing I2C at 0x40040b0,

with clock speed 0x2faf080

and SCL speed 0xc350

and prescale 0xc7

Start I2C at 0x40040b0,

with address 0x50

and r/w 0x0

NOACK

Write I2C at 0x40040b0,

with data 0x0,

with last 0x0

ACK

Write I2C at 0x40040b0,

with data 0x55,

with last 0x1

ACK

Start I2C at 0x40040b0,

with address 0x50

and r/w 0x0

NOACK

Write I2C at 0x40040b0,

with data 0x0,

with last 0x0

ACK

Start I2C at 0x40040b0,

with address 0x50

and r/w 0x1

NOACK

Read I2C at 0x40040b0,

with last 0x1

Data: 0x50dc5a0f

What I don't understand is why I am getting an NOACK response from the start transaction, but do get an ACK response from the following write transaction. Without a scope/logic analyser I am a bit stuck as to what could be going wrong.

Hope there is someone out there who has had a similar experience to me and will be able to help me out.