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Lee Lup Yuen 2023-06-30 16:37:59 +08:00
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README.md
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@ -755,21 +755,33 @@ Usernames and Passwords are...
![Yocto Plasma on Star64](https://lupyuen.github.io/images/star64-plasma.jpg)
# UART Output on Star64
# NuttX prints to QEMU Console
TODO
Our NuttX Kernel will print to the Serial Console for debugging. Before that, let's write some RISC-V Assembly Code to print to the QEMU Console!
From [System Memory Map](https://doc-en.rvspace.org/JH7110/TRM/JH7110_TRM/system_memory_map.html):
Earlier we ran NuttX on QEMU Emulator for 64-bit RISC-V...
UART0 is at 0x00_1000_0000
- ["64-bit RISC-V with Apache NuttX Real-Time Operating System"](https://lupyuen.github.io/articles/riscv)
From [UART Device Tree](https://doc-en.rvspace.org/VisionFive2/DG_UART/JH7110_SDK/general_uart_controller.html):
QEMU emulates a 16550 UART Port. (Similar to Star64 / JH7110)
UART Register base address "0x10000000" and range "0x10000"
From [nsh64/defconfig](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/star64/boards/risc-v/qemu-rv/rv-virt/configs/nsh64/defconfig#L10-L16):
[UART Datasheet](https://doc-en.rvspace.org/JH7110/Datasheet/JH7110_DS/uart.html)
```text
CONFIG_16550_ADDRWIDTH=0
CONFIG_16550_UART0=y
CONFIG_16550_UART0_BASE=0x10000000
CONFIG_16550_UART0_CLOCK=3686400
CONFIG_16550_UART0_IRQ=37
CONFIG_16550_UART0_SERIAL_CONSOLE=y
CONFIG_16550_UART=y
```
From [u16550_send](https://github.com/apache/nuttx/blob/master/drivers/serial/uart_16550.c#L1539-L1553):
Base Address of QEMU's UART Port is `0x1000` `0000`. (Same as Star64 / JH7110 yay!)
_How to print to the 16550 UART Port?_
Let's check the 16550 UART Driver in NuttX. From [u16550_send](https://github.com/apache/nuttx/blob/master/drivers/serial/uart_16550.c#L1539-L1553):
```c
/****************************************************************************
@ -787,7 +799,9 @@ static void u16550_send(struct uart_dev_s *dev, int ch)
}
```
[u16550_serialout](https://github.com/apache/nuttx/blob/master/drivers/serial/uart_16550.c#L610-L624)
[(u16550_serialout is defined here)](https://github.com/apache/nuttx/blob/master/drivers/serial/uart_16550.c#L610-L624)
To print a character, the driver writes to the UART Base Address (`0x1000` `0000`) at Offset UART_THR_OFFSET.
[UART_THR_OFFSET](https://github.com/apache/nuttx/blob/dc69b108b8e0547ecf6990207526c27aceaf1e2e/include/nuttx/serial/uart_16550.h#L172-L200) is 0:
@ -796,11 +810,11 @@ static void u16550_send(struct uart_dev_s *dev, int ch)
#define UART_THR_OFFSET (CONFIG_16550_REGINCR*UART_THR_INCR)
```
So we can transmit to UART0 by writing to `0x1000` `0000`. How convenient!
So we can transmit to UART Port by simply writing to `0x1000` `0000`. How convenient!
# NuttX on Star64
_How to print to the QEMU Console?_
TODO: Test printing in QEMU
Let's do the printing in RISC-V Assembly Code, so that we can debug the NuttX Boot Code.
From [qemu_rv_head.S](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/star64/arch/risc-v/src/qemu-rv/qemu_rv_head.S#L43-L64):
@ -824,7 +838,7 @@ From [qemu_rv_head.S](https://github.com/lupyuen2/wip-pinephone-nuttx/blob/star6
sb t1, 0(t0)
```
Output:
This prints "123" to the QEMU Console. Here's the output:
```text
+ qemu-system-riscv64 -semihosting -M virt,aclint=on -cpu rv64 -smp 8 -bios none -kernel nuttx -nographic
@ -833,7 +847,7 @@ NuttShell (NSH) NuttX-12.0.3
nsh>
```
Which is correct because QEMU is running with 8 CPUs.
Which is correct because QEMU is running with 8 CPUs. Yay!
[Cody AI Assistant](https://about.sourcegraph.com/cody) explains our RISC-V Assembly Code...
@ -843,6 +857,22 @@ And optimises our RISC-V Assembly Code...
![Cody AI Assistant optimises our RISC-V Assembly Code](https://lupyuen.github.io/images/riscv-cody2.png)
# UART Output on Star64
TODO: We'll take the UART Assembly Code from the previous section and run on Star64 / JH7110. (So we can troubleshoot the NuttX Boot Code)
From [System Memory Map](https://doc-en.rvspace.org/JH7110/TRM/JH7110_TRM/system_memory_map.html):
UART0 is at 0x00_1000_0000
From [UART Device Tree](https://doc-en.rvspace.org/VisionFive2/DG_UART/JH7110_SDK/general_uart_controller.html):
UART Register base address "0x10000000" and range "0x10000"
[UART Datasheet](https://doc-en.rvspace.org/JH7110/Datasheet/JH7110_DS/uart.html)
# NuttX on Star64
TODO: Embed Linux Kernel Header in QEMU
This is how we decode the RISC-V Linux Header...