PCHIP OS

An Operating system built for the Pchip.

Prerequisit

Install the rust programming language from the official website

Running

On qemu

cargo run

This will launch a serial port on your machine, and you will need to use a serial port console to connect to it.

If you wish to try the OS directly on your terminal, edit .cargo/config.toml: change pty to stdio on line 7.

On Pchip

The OS will run on the Pchip, but be aware that due to the various bug on the Pchip, the OS will not run correctly as of now.

Option 1: Run the OS from BRAM

ue to the size limit of BRAM (4k), PCHIP OS doesn't fit in BRAM anymore. If you wish to follow these steps, make sure you delete some code so that it is smaller than 4kb.

1. Change the linker script.

   In .cargo/config.toml, change the rustflags to use the pchip linker file:

   rustflags = ['-Clink-arg=-Tsrc/lds/pchip.lds', '-Ctarget-feature=-c']

2. Change the driver

   In src/uart.rs, change all instances of virt_uart to axi_uart_lite

3. generate the .mem files

   make gen_bram

   This will create 4 .mem files under the project root. These files can then be written into BRAM of the Bitstream using the Vivado tools. This is the same as the sd.c project. There should be a Makefile that does the rest of the conversions. Please ask Suezuku-San for details.

Option 2: Running the OS via Bootloader

Warning: I have not tried this as a bootloader isn't available on pchip yet.

Make sure your bootloader puts the code at address 0x8000_0000. If so, you should be able to keep using the virt.ld linker file. Otherwise you will need to write your own linker file. You will still need to change the UART driver as described above.

Using PCHIP OS

After the OS is booted, the following message is shown.

Hello world!
File status: false
Please select an Operation:
    h. Show this help message
    0. Trigger Breakpoint

After uploading a file/executable, the complete list will be shown

Please select an Operation:
    h. Show this help message
    0. Trigger Breakpoint
    1. Recieve a file
    2. Execute
    3. Show file in plain text
    4. Show file in hex
    5. Print value at memory address

Uploading files

This is tested with minicom on Linux.

1. Press 1 to initiate Xmodem Receiver on PCHIP OS. You should NOT press any keys on your keyboard, as Xmodem will be listening for a Xmodem Sender on UART.
2. To initiate Xmodem Sending in minicom, press ctrl-a and then s. Select Xmodem in the pop up window, and then choose the file you want to send. The transfer will start shortly.
3. After the file is sent, PCHIP OS will show the checksum of the received file. To verify the cksum on your host machine, you can execute cksum [FILENAME] in your terminal. If the checksum is correct, enter yes and the transfer will be complete.

Compile program to run on Pchip OS

Compile the program with:

• Base address at 0x9000_0000.
• Convert to binary format (elf is default)
• Call syscall 0 to exit the program

C example:

1. Write your program.

2. Add a system call at the end of the program. The system call will exit from the program and return control to the OS. Code for the system call:

   asm volatile ("li a0, 0; ecall;");

   If you want to add a breakpoint in your program, insert this line

   asm volatile ("ebreak;");

3. Compile the program with base address of 0x90000000 and convert to binary.

   Example Makefile:

   CROSSCOMPILE?=riscv64-unknown-elf-
   CC=${CROSSCOMPILE}gcc
   LD=${CROSSCOMPILE}ld
   OBJCOPY=${CROSSCOMPILE}objcopy
   CFLAGS=-ffreestanding
   LDFLAGS=-Ttext=0x90000000 -nostdlib
   
   main.bin: main.elf
       $(OBJCOPY) -S -O binary $^ $@
   
   main.elf: main.o
       $(LD) $(LDFLAGS) -o $@ $^
   
   %.o: %.c
       $(CC) $(CFLAGS) -c -o $@ $<
   
   clean::
       rm *.o *.elf *.bin

That's it! Compile your program and upload the .bin file to run in PCHIP OS!