nand2/06_IO_Devices/07_RTP

07 RTP

The special function register RTP memory mapped to addresses 4106 enables HACK to read bytes from the resistive touch panel controller chip AR1021 situated on MOD-LCD2.8RTP. The communication is protocol is SPI.

Attention: The specification of AR1200 requires, that SCK is inverted (compare 03_SPI/Readme.md with CPOL=1) and a slower transfer rate of max. 900kHz

Chip specification

IN/OUT	wire	function
IN	in[7:0]	byte to be sent.
IN	load	=1 initiates the transmission
OUT	out[15]	=0 chip is busy, =0 ready
OUT	out[7:0]	received byte
IN	SDI	serial data in
OUT	SDO	serial data out
OUT	SCK	serial clock

When load=1 transmission of byte in[7:0] is initiated. The byte is send to SDO bitwise together with 8 clock signals on SCK. At the same time RTP receives a byte at SDI. During transmission out[15] is 1. The transmission of a byte takes 256 clock cycles (32 cycles for each bit to achieve a slower transfer rate). Every 32 clock cycles one bit is shifted out. In the middle of each bit at counter number 31 the bit SDI is sampled. When transmission is completed out[15]=0 and RTP outputs the received byte to out[7:0].

Proposed Implementation

Use a Bit to store the state (0 = ready, 1 = busy) which is output to out[15]. Use a counter PC that counts from 0 to 511. Finally we need a BitShift8L. It will be loaded with the byte in[7:0] to be send. Use a Bit to sample the SDI line. After 8 bits are transmitted/received RTP cleares out[15] and outputs the received byte to in[7:0].

Attention: sample on rising edge of SCK and shift on falling edge of SCK.

Memory map

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

address	I/O device	R/W	function
4106	LCD	W	start transmittion of byte in[7:0]
4106	LCD	R	out[15]=1 busy, out[15]=0 idle, out[7:0] last received byte

RTP in real hardware

The board MOD-LCD2.8RTP comes with a resistive touch panel controlled by a controller chip AR1021. MOD-LCD2.8RTP must be connected to iCE40HX1K-EVB with 3 more jumper wire cables according to iCE40HX1K-EVB.pcf (Compare with schematic iCE40HX1K_EVB and MOD-LCD2.8RTP_RevB.pdf.

set_io RTP_SDI 7        # PIO3_3A connected to pin 13 of GPIO1
set_io RTP_SDO 8        # PIO3_3B connected to pin 15 of GPIO1
set_io RTP_SCK 9        # PIO3_5A connected to pin 17 of GPIO1

wire	iCE40HX1K-EVB (GPIO1)	MOD-LCD2.8RTP (UEXT)
+3.3V	3	+3.3V
GND	4	2 GND
LCD_DCX	5	7 D/C
LCD_SDO	7	8 MOSI
LCD_SCK	9	9 SCK
LCD_CSX	11	10 CS
RTP_SDI	13	4 IRQ/SDO (with solder jumper SJ3)
RTP_SDO	15	6 SDA
RTP_SCK	17	5 SCL

Attention: To enable SPI communication on the RTP controller chip AR1021 we must modify two solder jumpers. (Compare with schematic of MOD-LCD2.8RTP together with Datasheet of AR1021).

1. Cut connection SJ1-GND with a sharp cutter knife. (green)

2. Connect SJ1 to +3.3V to activate SPI mode of AR1021 (yellow)

3. Connect SJ3 (UEXT pin4 with SDO) (yellow)

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Project

• Implement special function register RTP and test with testbench:

  $ cd 07_RTP
  $ apio clean
  $ apio sim
  

• Compare output OUT of special chipRTP with CMP.

  

• Add special function registerRTP to HACK at memory addresses 4106 and upload to iCE40HX1K-EVB with bootloader boot.asm preloaded into ROM.

  $ cd ../05_GO
  $ make
  $ cd ../00_HACK
  $ apio clean
  $ apio upload
  

• Proceed to 07_Operating_System and implement the driver class Touch.jack that sends command over RTP the controller chip AR1021 on MOD-LCD2.8RTP