2020-01-05 12:42:37 +03:00
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Using PCI serial ports for debugging
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====================================
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Modern systems usually don't come with a built-in serial port anymore. This
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is unconvenient for low level debugging, since the serial port allows access
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to early boot log as well as kernel debugger, even when the display or keyboard
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are not working.
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It is fortunately possible to add a serial port over the PCI bus on machines
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which have appropriate expansion ports. This can be done using expresscard,
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mini-PCI, or PCI express ports.
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Devices known to work
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---------------------
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Dexlan XMT01A (https://www.accessoires-informatiques.com/Prix/EXPRESSCARD-PCIE-POUR-PORTABLE-23842.html)
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Uses MOSCHIP 9922 controller
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Devices to be tested
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--------------------
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https://smile.amazon.com/Industrial-Desktop-Bracket-Moschip-MCS9922/dp/B003D3MFHM/
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Configuring
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-----------
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- Install the card in your computer
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- Boot Haiku and look in the syslog for the PCI bus scan for the device:
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2021-08-24 18:45:36 +03:00
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.. code-block:: text
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KERN: PCI: [dom 0, bus 5] bus 5, device 0, function 0: vendor 9710, device 9922, revision 00
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KERN: PCI: class_base 07, class_function 00, class_api 02
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KERN: PCI: vendor 9710: MosChip Semiconductor Technology Ltd.
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KERN: PCI: device 9922: MCS9922 PCIe Multi-I/O Controller
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KERN: PCI: info: Communication controller (Serial controller, 16550)
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KERN: PCI: line_size 10, latency 00, header_type 80, BIST 00
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KERN: PCI: ROM base host 00000000, pci 00000000, size 00000000
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KERN: PCI: cardbus_CIS 00000000, subsystem_id 1000, subsystem_vendor_id a000
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KERN: PCI: interrupt_line 0b, interrupt_pin 01, min_grant 00, max_latency 00
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KERN: PCI: base reg 0: host 00004000, pci 0000KERN: 4000, size 00000008, flags 01
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KERN: PCI: base reg 1: host f1c01000, pci f1c01000, size 00001000, flags 00
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KERN: PCI: base reg 2: host 00000000, pci 00000000, size 00000000, flags 00
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KERN: PCI: base reg 3: host 00000000, pci 00000000, size 00000000, flags 00
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KERN: PCI: base reg 4: host 00000000, pci 00000000, size 00000000, flags 00
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KERN: PCI: base reg 5: host f1c00000, pci f1c00000, size 00001000, flags 00
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KERN: PCI: Capabilities: MSI, PM, PCIe
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KERN: PCI: Extended capabilities: Virtual Channel, Advanced Error Reporting
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2020-01-05 12:42:37 +03:00
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Write down the address of "base reg 0", this is where the serial port registers
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are mapped (it is probably possible to get this information from lspci on Linux
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as well?)
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Configure serial debug in config/settings/kernel/drivers/kernel:
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2021-08-24 18:45:36 +03:00
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.. code-block:: text
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serial_debug_output true
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serial_debug_speed 115200
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serial_debug_port 0x4000
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2020-01-05 12:42:37 +03:00
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Now your kernel is configured to send its output to the serial port. You can
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connect another machine to it (using an USB to serial adapter and a NULL modem
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cable, for example) and use SerialConnect or a similar tool to see the output
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and access the KDL prompt.
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Happy debugging!
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