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<!--
README.md - Description of sbc-harness
Copyright (C) 2024 Luke T. Shumaker <lukeshu@lukeshu.com>
SPDX-License-Identifier: AGPL-3.0-or-later
-->
# Building
Building requires cmake, make, an "arm-none-eabi" toolchain (including
newlib), and picotool (including the .cmake files;
eg. /usr/lib/cmake/picotool/*.cmake).
At the time of this writing, on Parabola GNU/Linux-libre that means:
- make 4.4.1-2
- cmake 3.30.3-1
- arm-none-eabi-binutils 2.42-1
- arm-none-eabi-gcc 14.1.0-1
- arm-none-eabi-newlib 4.4.0.20231231-1
- picotool 2.0.0-2
```bash
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make
```
# Debugging
UART:
- pin1: gpio0: TX (so connect it to your FTDI's RX)
- pin2: gpio1: RX (so connect it to your FTDI's TX)
- pin3: gnd (so connect it to your FTDI's GND)
- `picocom --baud=115200 /dev/ttyUSB0`
- `picocom --baud=115200 /dev/ttyACM0`
- `openocd -f interface/cmsis-dap.cfg -c 'set USE_CORE 0' -f target/rp2040.cfg -c "adapter speed 5000"`
(Explanation of `USE_CORE`: https://github.com/raspberrypi/debugprobe/issues/45)
- `arm-none-eabi-gdb ./build/rp2040/cmd/sbc_harness/sbc_harness.elf`
```
target extended-remote localhost:3333
monitor reset init
continue
```
https://openocd.org/doc/html/General-Commands.html
SWD:
- https://www.raspberrypi.com/documentation/microcontrollers/debug-probe.html
- https://github.com/raspberrypi/debugprobe
- https://developer.arm.com/documentation/101451/0100/About-CMSIS-DAP
## Raspberry Pi 3-pin Debug Connector
- https://datasheets.raspberrypi.com/debug/debug-connector-specification.pdf
| Pin # | UART | ARM SW-DP | cJTAG (IEEE 1149.7) |
|-------|----------------------|------------------------------------|----------------------------------|
| 1 | RX (targetâdebugger) | SC/SWCLK (serial clock) | TMSC - Test Clock Control |
| 2 | GND | GND | GND |
| 3 | TX (targetâdebugger) | SD/SWDIO (bidi serial data) | TCKC - Test Master/Slave Control |
| | | SWO (optional: serial wire output) | |
## UART (Universal asynchronous receiver/transmitter)
## ARM SWD (Serial Wire Debug)
- https://developer.arm.com/documentation/101761/1-0/Debug-and-trace-interface/Serial-Wire-Debug-signals
- https://developer.arm.com/documentation/ihi0031/a/The-Serial-Wire-Debug-Port--SW-DP-/Introduction-to-the-ARM-Serial-Wire-Debug--SWD--protocol
- https://arm-software.github.io/CMSIS-DAP/latest/index.html
- ADIv5: https://developer.arm.com/documentation/ihi0031/g/
- ADIv6: https://developer.arm.com/documentation/ihi0074/e/
Alternative to Raspberry Pi Debug Probe:
https://oshwlab.com/wagiminator/samd11c-swd-programmer which uses
https://github.com/ataradov/free-dap instead of ARM's reference CMSIS
implementation
Note that the RP2040 chip has a pure SW-DP (just speaks SWD), not a
JTAG-DP (just speaks JTAG) or a SWJ-DP (can speak either SWD or JTAG).
```
+-[Host PC]-------------------------+
| |
| +-----+ |
| | GDB | |
| +-----+ |
| ^ |
| | GDB Remote Serial Protocol
| | on localhost:3333
| V |
| +---------+ |
| | OpenOCD | |
| +---------+ |
| ^ |
| | |
+-----------------|-----------------+
USB-A
|
| ARM CMSIS-DAP protocol
| (a USB-based protocol)
|
(micro)USB-B
+-[Debug Probe]-------+
| | |
| V |
| +----------------+ |
| | ARM's | |
| | reference | |
| | CMSIS-DAP | |
| | implementation | |
| +----------------+ |
| ^ |
| | |
+----------|----------+
SW-DP (3-pin JST-SH)
|
| ADIv5 SWD protocol
|
SW-DP (3 .1" headers)
+-[SBC-Harness]---|-----------------+
| | |
| ,---------------' |
| | |
| | +----------------------------+ |
| | | Cortex-M0+ | |
| | | +------------------------+ | |
| +--->| CoreSight ADIv5 module | | |
| | | +------------------------+ | |
| | +----------------------------+ |
| | |
| | +----------------------------+ |
| | | Cortex-M0+ | |
| | | +------------------------+ | |
| `--->| CoreSight ADIv5 module | | |
| | +------------------------+ | |
| +----------------------------+ |
| |
+-----------------------------------+
```
# Usage
The harness uses DHCP to acquire an IPv4 address, then serves the 9P
protocol over TCP:
- TCP port: 564 (9P does not have a standard TCP port number, but
this is the default port number used by most 9P-over-TCP clients,
including the Linux kernel's v9fs driver).
- Supported protocol versions:
- `9P2000` (base protocol): Yes
- `9P2000.u` (Unix extension): Yes, with Linux kernel
architecture-"generic" errnos. This will match the Linux kernel
errnos on most architectures (but, as of Linux v6.7, not on
Alpha, MIPS, PA-RISC, PowerPC, or SPARC; I am unsure whether on
these platforms the kernel's v9fs filesystem driver will map the
"generic" errnos to the architecture-specific errnos for you).
- `9P2000.L` (Linux extension): No, it's an abomination and
unlikely to ever be supported
- `9P2000.e` (Erlang extension): No, but if you want it and ask
nicely I'd be happy to add it (I'm not sure why you'd want it
though).
- Authentication: None
There are lots of 9P clients that you can use. 9P is a filesystem
protocol; and you can mount it directly with the the Linux kernel's
v9fs filesystem driver, with plan9port's `9pfuse`; or interact with it
without mounting it using the shell commands `9p` (from plan9port),
`wmiir`, `ixpc`; or interact with it without mounting it by using a
library for your programming language of choice.
Some notes on choosing a client:
- On x86-32, the Linux kernel v9fs driver is known to drop entries
from directory listings; I advise using 9pfuse instead of you want
to mount it on 32-bit systems.
- I generally like mounting it as a real filesystem, but this means
that you only get errno errors, and the more-helpful error strings
are discarded.
- The sbc-harness only supports 8 concurrent connections to the 9P
server, so while shell commands are handy for poking around, for
real use where you're doing things in parallel you'll likely want
to mount it or use a library that can reuse existing connections.
# Bugs/Limitations
- Only supports 8 concurrent TCP connectsions to the 9P server (due
to limitations in the W5500 TCP-offload chip; TODO: investigate
using a software TCP/IP stack with the W5500 in MAC-raw mode)
- Only supports 16 concurrent 9P requests (I wanted a static limit,
and "connections*2" seemed reasonable)
- Only supports IPv4, not IPv6 (due to limitations in the W5500
TCP-offload chip; TODO: investigate upgrading to the W6100 or using
a software TCP/IP stack with the W5500 in MAC-raw mode)
|
