nand2/06_IO_Devices/03_SPI

03 SPI

The special function register SPI memory mapped to address 4100 enables HACK to read/write bytes from the spi flash memory chip W25Q16BV situated on iCE40HX1K-EVB. The timing diagramm for SPI communication looks like the following diagram (we use CPOL=0 and CPHA=0).

Chip specification

IN/OUT	wire	function
IN	in[7:0]	byte to be sent.
IN	in[8]	=0 (and load=1) send byte and set CSX low
IN	in[8]	=1 (and load =1) pull CSX high without sending byte
IN	load	=1 initiates the transmission, when in[8]=0
OUT	out[15]	=0 chip is busy, =0 chip is ready
OUT	out[7:0]	received byte (when out[15]=0)
OUT	CSX	chip select not
OUT	SDO	serial data out
OUT	SCK	serial clock
IN	SDI	serial data in

When load=1 and in[8]=0 transmission of byte in[7:0] is initiated. CSX is goes low (and stays low even when transmission is completed). The byte is send to SDO bitwise together with 8 clock signals on SCK. At the same time the SPI receives a byte at SDI. During transmission out[15] is 1. After 16 clock cycles the transmission of one byte is completed. out[15] goes low and SPI outputs the received byte to out[7:0].

When load=1 and in[8]=1 CSX goes high without transmission of any bit.

Attention: Sampling of SDO is done at rising edge of SCK and shifting is done at falling edge of SCK.

Proposed Implementation

Use a Bit to store the state (0 = ready, 1 = busy) which is output to out[15]. Use a counter PC to count from 0 to 15. Finally we need a BitShift8L. This will be loaded with the byte in[7:0] to be send. Another Bit will sample the SDI wire when SCK=0 and shift the stored bit into the BitShift8L when SCK=1. After 8 bits are transmitted the module cleares out[15] and outputs the received byte to out[7:0].

Memory map

The special function register SPI is mapped to memory map of HACK according to:

address	I/O device	R/W	function
4100	SPI	R	out[15]=1 if busy, out[7:0] received byte
4100	SPI	W	start transmittion of byte in[7:0]

cat.asm

To test HACK with SPI we need a little machine language programm cat.asm, which reads 4 consecutive bytes of SPI flash memory chip W25Q16BV of iCE40HX1K-EVB, starting at address 0x040000 (256k) and sends them to UART_TX.

According to the datasheet of spi flash rom chip W25Q16BV the commands needed to read the flash rom chip are:

command	function
0xAB	wake up from deep power down (wait 3us) before launching next command.
0x03 0x04 0x00 0x00	read data (command 0x03) starting at address 0x040000 (256k)
0xB9	go in power down

SPI in real hardware

The board iCE40HX1K-EVB comes with a SPI flash rom chip W25Q16BV. The chip is already connected to iCE40HX1K according iCE40HX1K-EVB.pcf (Compare with schematic iCE40HX1K_EVB.

set_io SPI_SDO 45 # iCE40-SDO
set_io SPI_SDI 46 # iCE40-SDI
set_io SPI_SCK 48 # iCE40-SCK
set_io SPI_CSX 49 # iCE40-SS_B

---

Project

• Implement SPI.v and test with testbench:

  $ cd 03_SPI
  $ apio clean
  $ apio sim
  

• Compare output OUT of special function tregister SPI with CMP.

  

• Add special function registerSPI to HACK.v at memory address 4100.

• Implement cat.asm and test in simulation:

  $ cd 03_SPI
  $ make
  $ cd ../00_HACK
  $ apio clean
  $ apio sim
  

• Check the wake up command 0xAB:

  

• Check command 0x03040000 (read from address 0x040000)

  

• Check reading of string "SPI!" output to UartTX.

  

• preload the SPI memory chip with some text file at address 0x040000.

• build and upload HACK with cat.asm in ROM.BIN to iCE40HX1K-EVB.

  $ echo SPI! > spi.txt
  $ iceprogduino -o 256k -w spi.txt
  $ cd 00_HACK
  $ apio clean
  $ apio upload
  $ tio /dev/ttyACM0
  

• Check if you see "SPI!" in your terminal.