Any read materials to understand uart device driver architecture in FreeBSD.

Rajesh Kumar rajfbsd at
Fri Jul 13 09:41:33 UTC 2018

Hi blubee,

Thanks for your quick response.

Definitely, these two books are good reads. But, I was looking for some
information regarding the code design from the perspective of existing uart
code base in FreeBSD source (sys/dev/uart), not just generic device driver
concepts and overall system architecture. Anyway, thanks again for your

On Fri, Jul 13, 2018 at 2:40 PM blubee blubeeme <gurenchan at> wrote:

> On Fri, Jul 13, 2018, 16:57 Rajesh Kumar <rajfbsd at> wrote:
>> Hi,
>> I am trying to understand the uart device drivers architecture in FreeBSD.
>> I see the following set of file in sys/dev/uart.
>> a) uart_bus_xxxx -> one file each for acpi, pci, isa bus etc.,
>> b) uart_core - uart common routines
>> c) uart_cpu_xxxx -> one file each for x86, powerpc etc.,
>> d) uart_dev_xxxx -> I assume this is one file each for seperate uart IP's.
>> e) some other files.
>> Questions :
>> a) Is there any good read materials to understand the uart driver
>> architecutre (from code perspective) in FreeBSD?
>> b) If I need to write a new uart driver for a uart IP, what are the things
>> to do? I assume i need to have a seperate uart_dev_* file and need to add
>> that device ID in appropriate uart_bus_* file? what other things I need to
>> take care?
>> c) In uart_bus_acpi.c and uart_bus_isa.c, I see the definitions of
>> acpi_ns8250_ids and isa_ns8250_ids list.  Where are those ID's derived
>> from? I understand PNP ID, ACPI ID and PCI Vendor and Device ID, but not
>> sure about those above mentioned IDs?
>> Thanks,
>> Rajesh.
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> Writing drivers:
> FreeBSD architecture:

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