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Documentation/superio: add formatting to generic PNP documentation 

Change-Id: Id12ec4d5f11f4285a1379cf32a5d0f6cd2ce9e70
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38519
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Felix Held 2020-01-22 18:48:39 +01:00 committed by Patrick Georgi
parent fab9ae8167
commit b39bc2510e
1 changed files with 23 additions and 23 deletions
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46
Documentation/superio/common/pnp.md
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@ -15,13 +15,13 @@ specification is still the main reference though.
Super I/O chips connected via LPC to the southbridge usually have their
I/O-mapped configuration interface with a size of two bytes at the base
address 0x2e or 0x4e. Other PNP devices have their configuration
address `0x2e` or `0x4e`. Other PNP devices have their configuration
interface at other addresses.
The two byte registers allow access to an indirect 256 bytes big
register space that contains the configuration. By writing the index
to the lower byte (e.g. 0x2e), you can access the register contents at
that index by reading/writing the higher byte (e.g. 0x2f).
register space that contains the configuration. By writing the index to
the lower byte (e.g. `0x2e`), you can access the register contents at
that index by reading/writing the higher byte (e.g. `0x2f`).
To prevent accidental changes of the Super I/O (SIO) configuration,
the SIOs need a configuration mode unlock sequence. After changing the
@ -31,18 +31,18 @@ the configuration mode lock sequence.
## Logical device numbers (LDN)
Each PNP device can contain multiple logical devices. The bytes from
0x00 to 0x2f in the indirect configuration register space are common
for all LDNs, but some SIO chips require a certain LDN to be selected
in order to write certain registers in there. An LDN gets selected by
writing the LDN number to the LDN select register 0x07. Registers 0x30
to 0xFF are specific to each LDN number.
`0x00` to `0x2f` in the indirect configuration register space are common
for all LDNs, but some SIO chips require a certain LDN to be selected in
order to write certain registers in there. An LDN gets selected by
writing the LDN number to the LDN select register `0x07`. Registers
`0x30` to `0xff` are specific to each LDN number.
coreboot encodes the physical LDN number in the lower byte of the LDN
number.
### Virtual logical device numbers
Register 0x30 is the LDN enable register and since it is an 8 bit
Register `0x30` is the LDN enable register and since it is an 8 bit
register, it can contain up to 8 enable bits for different parts of
the functionality of that logical device. To set a certain enable bit
in one physical LDN, the concept of virtual LDNs was introduced.
@ -54,7 +54,7 @@ part in the lower 3 bits of the higher byte of the LDN number.
## I/O resources
Starting at register address 0x60, each LDN has 2 byte wide I/O base
Starting at register address `0x60`, each LDN has 2 byte wide I/O base
address registers. The size of an I/O resource is always a power of
two.
@ -67,29 +67,29 @@ number of LSBs being zero, which can also be zero if the LSB is a one,
the resource has N address bits and a size of 2\*\*N bytes. The mask
address is also the highest possible address to map the I/O region.
A typical example for an I/O resource mask is 0x07f8 which is
0b0000011111111000 in binary notation. The three LSBs are zeros here,
A typical example for an I/O resource mask is `0x07f8` which is
`0b0000011111111000` in binary notation. The three LSBs are zeros here,
so it's an eight byte I/O resource with three address offset bits
inside the resource. The highest base address it can be mapped to is
0x07f8, so the region will end at 0x07ff.
`0x07f8`, so the region will end at `0x07ff`.
The Super I/O datasheets typically contain the information about the
I/O resource masks. On most Super I/O chips the mask can also be found
out by writing 0xffff to the corresponding I/O base address register
out by writing `0xffff` to the corresponding I/O base address register
and reading back the value; since the lowest and highest bits are
hard-wired to zero according to the I/O resource size and maximal
possible I/O address, this gives the mask.
## IRQ resources
Each physical LDN has up to two configurable interrupt request
register pairs 0x70, 0x71 and 0x72, 0x73. Each pair can be configured
to use a certain IRQ number. Writing 1 to 15 into the first register
Each physical LDN has up to two configurable interrupt request register
pairs `0x70`, `0x71` and `0x72`, `0x73`. Each pair can be configured to
use a certain IRQ number. Writing 1 to 15 into the first register
selects the IRQ number generated by the corresponding IRQ source and
enables IRQ generation; writing 0 to it disables the generation of
IRQs for the source. The second register selects the IRQ type (level
or edge) and IRQ level (high or low). For LPC SIOs the IRQ type is
hard-wired to edge.
enables IRQ generation; writing 0 to it disables the generation of IRQs
for the source. The second register selects the IRQ type (level or edge)
and IRQ level (high or low). For LPC SIOs the IRQ type is hard-wired to
edge.
On the LPC bus a shared SERIRQ line is used to signal IRQs to the
host; the IRQ number gets encoded by the number of LPC clock cycles
@ -106,7 +106,7 @@ number. The quiet mode is often broken.
## DRQ resources
Each physical LDN has two legacy ISA-style DMA request channel
registers at 0x74 and 0x75. Those are only used for legacy devices
registers at `0x74` and `0x75`. Those are only used for legacy devices
like parallel printer ports or floppy disk controllers.
Each device using LPC legacy DMA needs its own LDMA line to the host.