112 lines
4.5 KiB
Markdown
112 lines
4.5 KiB
Markdown
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## 01 UartTX
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The special function register `UartTX` mapped to memory address 4098 enables HACK to send chars to the outer world over UART with 115200 baud 8N1. The timing diagramm for the TX wire should look like:
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During idle TX line is high (logic 1). Transmission of a byte (8 bits) is initiated by the so called start bit, which always is low (logic 0), followed by the 8 data bits, starting with the least significant bit. The transmission is finished by sending the stop bit, which always is high (logic 1).
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This protocoll is refered as 8N1 meaning (8 data bits, no parity bit, 1 stop bit). We use a transmission speed of 115200 baud (bits per second), meaning that each bit takes 1s/115200 = 8.68us or 217 cycles of the internal 25MHz clock clk.
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### Chip specification
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| IN/OUT | wire | function |
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| ------ | ------- | --------------------------------------------------- |
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| IN | in[7:0] | byte to be sent. |
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| IN | load | =1 initiates the transmission |
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| OUT | out[15] | =1 chip is busy, =0 chip is ready to send next byte |
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| OUT | TX | transmission wire |
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When load = 1 the chip starts serial transmission of the byte in[7:0] to the TX line according to the protocoll 8N1 with 115200 baud. During transmission out[15] is set to high (busy). The transmission is finished after 2170 clock cycles (10 byte a 217 cycle each). When transmission completes out[15] goes low again (ready).
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### Proposed Implementation
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Use a `Bit` to store the state (0 = ready, 1 = busy). Use a counter `PC` to count from 0 to 216. When clocked at 25MHz, this counter will produce the baudrate of 115200 bits per second. A second counter `PC` counts from 0 to 9 (the 10 bits to send). Finally we need a `BitShift9R`. This will be loaded with the bit pattern to be send (startbit, 8 data bits).
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### memory map
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The special function register `UartTX` is mapped to memory map of HACK according to:
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| address | I/O device | R/W | function |
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| ------- | ---------- | --- | ------------------------------------- |
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| 4098 | UART_TX | R | out[15]=1 if busy, out[15]=0 if ready |
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| 4098 | UART_TX | W | send char in[7:0] to TX |
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### hello.asm
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To test HACK with `UartTX` we need a little machine language programm `hello.asm`, which sends the String "Hi" to UART.
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**Attention:** Use a loop to wait until UartTX is ready to send the next byte.
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### UartTX in real hardware
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The programmer Olimexino 32u4 can also be used as bridge to connect the PC to iCE40HX1K-EVB over UART. This can be done with the 10 wire UEXT cable which goes into the PGM1 connector of iCE40HX1K-EVB.
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**Note:** To connect RX and TX lines of UEXT-connector with iCE40-chip on iCE40-HX1K-EVB find the solder-jumper-pads RxD_E1 and TxD_E1 near the UEXT connector (refer to [datasheets/iCE40HX1K-EVB](../datasheets/iCE40HX1K-EVB_Rev_B.pdf)) and solder them together as in the foto below.
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The programmer olimexino 32u4 works in two different mode:
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- Mode 1 (yellow led on): programmer of iCE40-board. Used with iceprogduino.
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- Mode 2 (green led on): UART Bridge to iCE40 chip. Use with terminal programm (e.g. tio or screen on linux).
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To switch between the modes press the hardware button on olimexino 32u4 (HWB).
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Now iCE40HX1K is connected to RX,TX of olimexino 32u4 according to `iCE40HX1K-EVB.pcf`. (Check by comparing the schematic of iCE40HX1K-EVB).
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```
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set_io UART_RX 36 # PIO2_8/RxD connected to pin 3 of UEXT (PGM)
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set_io UART_TX 37 # PIO2_9/TxD connected to pin 4 of UEXT (PGM)
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```
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***
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### Project
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* Implement `UartTX` and simulate with testbench.
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```
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$ cd 01_UartTX
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$ apio clean
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$ apio sim
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```
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* Compare with CMP:
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* Edit `HACK` and add the special function register `UartTX` to the memory address 4098.
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* Implement `hello.asm` and run in simulation:
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```
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$ cd 01_UartTX
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$ make
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$ cd ../00_HACK
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$ apio clean
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$ apio sim
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```
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* Check the TX wire of the simulation and look for the transmission of "Hi".
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* build and upload HACK with `hello.asm` in ROM.BIN to iCE40HX1K-EVB.
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* switch olimexino 32u4 to UART-Bridge
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* open Terminal on your computer
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* press reset button on iCE40HX1K-EVB and see if wou can recieve "Hi" on your Computer.
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```
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$ cd 00_HACK
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$ apio clean
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$ apio upload
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$ tio /dev/ttyACM0
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```
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