From 6ca34a59b582f885bffa9186c83894a1a3a55ef2 Mon Sep 17 00:00:00 2001
From: Adrien Destugues <pulkomandy@pulkomandy.tk>
Date: Sun, 5 Jan 2020 10:42:37 +0100
Subject: [PATCH] Add some notes on how to use PCI serial ports for serial
 debugging.

---
 docs/develop/kernel/pci_serial_debug.txt | 64 ++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 docs/develop/kernel/pci_serial_debug.txt

diff --git a/docs/develop/kernel/pci_serial_debug.txt b/docs/develop/kernel/pci_serial_debug.txt
new file mode 100644
index 0000000000..2eb8dd1903
--- /dev/null
+++ b/docs/develop/kernel/pci_serial_debug.txt
@@ -0,0 +1,64 @@
+Using PCI serial ports for debugging
+====================================
+
+Modern systems usually don't come with a built-in serial port anymore. This
+is unconvenient for low level debugging, since the serial port allows access
+to early boot log as well as kernel debugger, even when the display or keyboard
+are not working.
+
+It is fortunately possible to add a serial port over the PCI bus on machines
+which have appropriate expansion ports. This can be done using expresscard,
+mini-PCI, or PCI express ports.
+
+Devices known to work
+---------------------
+
+Dexlan XMT01A (https://www.accessoires-informatiques.com/Prix/EXPRESSCARD-PCIE-POUR-PORTABLE-23842.html)
+	Uses MOSCHIP 9922 controller
+
+Devices to be tested
+--------------------
+
+https://smile.amazon.com/Industrial-Desktop-Bracket-Moschip-MCS9922/dp/B003D3MFHM/
+
+Configuring
+-----------
+
+- Install the card in your computer
+- Boot Haiku and look in the syslog for the PCI bus scan for the device:
+
+KERN: PCI: [dom 0, bus  5] bus   5, device  0, function  0: vendor 9710, device 9922, revision 00
+KERN: PCI:   class_base 07, class_function 00, class_api 02
+KERN: PCI:   vendor 9710: MosChip Semiconductor Technology Ltd.
+KERN: PCI:   device 9922: MCS9922 PCIe Multi-I/O Controller
+KERN: PCI:   info: Communication controller (Serial controller, 16550)
+KERN: PCI:   line_size 10, latency 00, header_type 80, BIST 00
+KERN: PCI:   ROM base host 00000000, pci 00000000, size 00000000
+KERN: PCI:   cardbus_CIS 00000000, subsystem_id 1000, subsystem_vendor_id a000
+KERN: PCI:   interrupt_line 0b, interrupt_pin 01, min_grant 00, max_latency 00
+KERN: PCI:   base reg 0: host 00004000, pci 0000KERN: 4000, size 00000008, flags 01
+KERN: PCI:   base reg 1: host f1c01000, pci f1c01000, size 00001000, flags 00
+KERN: PCI:   base reg 2: host 00000000, pci 00000000, size 00000000, flags 00
+KERN: PCI:   base reg 3: host 00000000, pci 00000000, size 00000000, flags 00
+KERN: PCI:   base reg 4: host 00000000, pci 00000000, size 00000000, flags 00
+KERN: PCI:   base reg 5: host f1c00000, pci f1c00000, size 00001000, flags 00
+KERN: PCI:   Capabilities: MSI, PM, PCIe
+KERN: PCI:   Extended capabilities: Virtual Channel, Advanced Error Reporting
+
+
+Write down the address of "base reg 0", this is where the serial port registers
+are mapped (it is probably possible to get this information from lspci on Linux
+as well?)
+
+Configure serial debug in config/settings/kernel/drivers/kernel:
+
+serial_debug_output true
+serial_debug_speed 115200
+serial_debug_port 0x4000
+
+Now your kernel is configured to send its output to the serial port. You can
+connect another machine to it (using an USB to serial adapter and a NULL modem
+cable, for example) and use SerialConnect or a similar tool to see the output
+and access the KDL prompt.
+
+Happy debugging!