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caravel/docs/other/gpio.txt

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Added more documentation, fully documenting the GPIO, and various aspects of the memory mapped controls for the management protection, and the various differences between the Caravel and Caravan chips.
2021-12-23 10:54:36 -06:00
Caravel GPIO
----------------------------
The Caravel GPIO pins are multi-purpose pins capable of being configured
for numerous applications, including digital input, output, analog
signaling, with slew rate control, transition level control, and weak
pull-up and pull-down functions.
The GPIO pins are configured to operate either under the control of the
Caravel management SoC or under the control of the user project. When
used under management SoC control, certain pins have certain special
functions.
--------------------------------------------------------------------------
Register name = reg_mprj_io_0
Memory location = 0x26000024
Housekeeping SPI location = 0x1d, 0x1e
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x1e |analog |analog |analog | mode | input | hold | output| mgmt |
| |polar. |select |enable | select|disable| over | enb | enable|
+------+-------+-------+-------+-------+-------+-------+-------+-------+
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x1d | | | |digital|digital|digital| trip | slow |
| | | | |mode 0 |mode 1 |mode 2 | point | slew |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
bit 0: Management enable (bit field MGMT_ENABLE)
value 0 = User project controls the GPIO pin
value 1 = Management SoC controls the GPIO pin
bit 1: Output enable bar (output disable) (bit field OUTPUT_DISABLE)
value 0 = Pad enabled for digital output
value 1 = Pad disabled for digital output
bit 2: Holdover (bit field HOLD_OVERRIDE)
value 0 = all I/O latched during hold mode
value 1 = only inputs latched during hold mode
NOTE: The GPIO cannot be placed in hold mode in this version
of Caravel.
bit 3: Input disable (bit field INPUT_DISABLE)
value 0 = Pin enabled for digital input
value 1 = Pin disabled for digital input
bit 4: Input buffer Mode select (bit field MODE_SELECT)
value 0 = CMOS/LVTTL mode (see trip point value, below)
value 1 = Input buffer compliant with 1.8V external signals
(VIL = 0.54V; VIH = 1.26V). Overrides the trip
point setting.
bit 5: Analog enable (bit field ANALOG_ENABLE)
value 0 = analog busses disconnected
value 1 = analog busses connected
The analog function is intended for a type of switched-capacitor
operation on the inputs. Its use is limited in Caravel.
bits 6-7: Analog select and polarity (bit field ANALOG_SELECT | ANALOG_POLARITY)
(value = {out, bit[7], bit[6], out} in the list below)
value 000 = connect pad to VSSIO
value 001 = connect pad to analog A bus
value 010 = connect pad to VSSIO
value 011 = connect pad to analog B bus
value 100 = connect pad to analog A bus
value 101 = connect pad to VDDIO
value 110 = connect pad to analog B bus
value 111 = connect pad to VDDIO
bit 8: Slow slew (bit field SLOW_SLEW_MODE)
value 0 = Fast output slew rate
value 1 = Slow output slew rate
bit 9: Trip point (bit field TRIPPOINT_SEL)
value 0 = CMOS (VIL = 0.3 * VDDIO; VIH = 0.7 * VDDIO)
value 1 = LVTTL (VIL = 0.8V; VIH = 2.0V)
The value determines what input voltage is converted to a
0 or 1 bit by the input buffer. Value 0 is appropriate
for CMOS operation; value 1 is appropriate for LVTTL
operation. When the VDDIO power supply is less than 2.7V,
then the trip point is always in CMOS mode. See also
the input buffer mode select, above.
bits 10-12: Digital mode (bit field DIGITAL_MODE_MASK)
(value = {bit[12], bit[11], bit[10]} in the list below)
value 000 = analog mode
value 001 = analog mode
value 010 = digital input, 5kohm pull-up
value 011 = digital input, 5kohm pull-up
value 100 = open drain to power
value 101 = open drain to ground
value 110 = digital output
value 111 = digital output (weak)
The remaining I/O configuration registers have the same form as above.
The memory mapped addresses are as follows:
Register name = reg_mprj_io_1
Memory location = 0x26000028
Housekeeping SPI location = 0x1f, 0x20
Register name = reg_mprj_io_2
Memory location = 0x2600002c
Housekeeping SPI location = 0x21, 0x22
Register name = reg_mprj_io_3
Memory location = 0x26000030
Housekeeping SPI location = 0x23, 0x24
Register name = reg_mprj_io_4
Memory location = 0x26000034
Housekeeping SPI location = 0x25, 0x26
Register name = reg_mprj_io_5
Memory location = 0x26000038
Housekeeping SPI location = 0x27, 0x28
Register name = reg_mprj_io_6
Memory location = 0x2600003c
Housekeeping SPI location = 0x29, 0x2a
Register name = reg_mprj_io_7
Memory location = 0x26000040
Housekeeping SPI location = 0x2b, 0x2c
Register name = reg_mprj_io_8
Memory location = 0x26000044
Housekeeping SPI location = 0x2d, 0x2e
Register name = reg_mprj_io_9
Memory location = 0x26000048
Housekeeping SPI location = 0x2f, 0x30
Register name = reg_mprj_io_10
Memory location = 0x2600004c
Housekeeping SPI location = 0x31, 0x32
Register name = reg_mprj_io_11
Memory location = 0x26000050
Housekeeping SPI location = 0x33, 0x34
Register name = reg_mprj_io_12
Memory location = 0x26000054
Housekeeping SPI location = 0x35, 0x36
Register name = reg_mprj_io_13
Memory location = 0x26000058
Housekeeping SPI location = 0x37, 0x38
Register name = reg_mprj_io_14
Memory location = 0x2600005c
Housekeeping SPI location = 0x39, 0x3a
Register name = reg_mprj_io_15
Memory location = 0x26000060
Housekeeping SPI location = 0x3b, 0x3c
Register name = reg_mprj_io_16
Memory location = 0x26000064
Housekeeping SPI location = 0x3d, 0x3e
Register name = reg_mprj_io_17
Memory location = 0x26000068
Housekeeping SPI location = 0x3f, 0x40
Register name = reg_mprj_io_18
Memory location = 0x2600006c
Housekeeping SPI location = 0x41, 0x42
Register name = reg_mprj_io_19
Memory location = 0x26000070
Housekeeping SPI location = 0x43, 0x44
Register name = reg_mprj_io_20
Memory location = 0x26000074
Housekeeping SPI location = 0x45, 0x46
Register name = reg_mprj_io_21
Memory location = 0x26000078
Housekeeping SPI location = 0x47, 0x48
Register name = reg_mprj_io_22
Memory location = 0x2600007c
Housekeeping SPI location = 0x49, 0x4a
Register name = reg_mprj_io_23
Memory location = 0x26000080
Housekeeping SPI location = 0x4b, 0x4c
Register name = reg_mprj_io_24
Memory location = 0x26000084
Housekeeping SPI location = 0x4d, 0x4e
Register name = reg_mprj_io_25
Memory location = 0x26000088
Housekeeping SPI location = 0x4f, 0x50
Register name = reg_mprj_io_26
Memory location = 0x2600008c
Housekeeping SPI location = 0x51, 0x52
Register name = reg_mprj_io_27
Memory location = 0x26000090
Housekeeping SPI location = 0x53, 0x54
Register name = reg_mprj_io_28
Memory location = 0x26000094
Housekeeping SPI location = 0x55, 0x56
Register name = reg_mprj_io_29
Memory location = 0x26000098
Housekeeping SPI location = 0x57, 0x58
Register name = reg_mprj_io_30
Memory location = 0x2600009c
Housekeeping SPI location = 0x59, 0x5a
Register name = reg_mprj_io_31
Memory location = 0x260000a0
Housekeeping SPI location = 0x5b, 0x5c
Register name = reg_mprj_io_32
Memory location = 0x260000a4
Housekeeping SPI location = 0x5d, 0x5e
Register name = reg_mprj_io_33
Memory location = 0x260000a8
Housekeeping SPI location = 0x5f, 0x60
Register name = reg_mprj_io_34
Memory location = 0x260000ac
Housekeeping SPI location = 0x61, 0x62
Register name = reg_mprj_io_35
Memory location = 0x260000b0
Housekeeping SPI location = 0x63, 0x64
Register name = reg_mprj_io_36
Memory location = 0x260000b4
Housekeeping SPI location = 0x65, 0x66
Register name = reg_mprj_io_37
Memory location = 0x260000b8
Housekeeping SPI location = 0x67, 0x68
The bit value of the 13-bit static configuration GPIO setting is difficult
to remember, so the "defs.h" file (included when compiling a C program for
the management SoC) contains some definitions for typical useful configuration
values, as follows:
#define GPIO_MODE_MGMT_STD_INPUT_NOPULL 0x0403
#define GPIO_MODE_MGMT_STD_INPUT_PULLDOWN 0x0803
#define GPIO_MODE_MGMT_STD_INPUT_PULLUP 0x0c03
#define GPIO_MODE_MGMT_STD_OUTPUT 0x1809
#define GPIO_MODE_MGMT_STD_BIDIRECTIONAL 0x1801
#define GPIO_MODE_MGMT_STD_ANALOG 0x000b
#define GPIO_MODE_USER_STD_INPUT_NOPULL 0x0402
#define GPIO_MODE_USER_STD_INPUT_PULLDOWN 0x0802
#define GPIO_MODE_USER_STD_INPUT_PULLUP 0x0c02
#define GPIO_MODE_USER_STD_OUTPUT 0x1808
#define GPIO_MODE_USER_STD_BIDIRECTIONAL 0x1800
#define GPIO_MODE_USER_STD_OUT_MONITORED 0x1802
#define GPIO_MODE_USER_STD_ANALOG 0x000a
GPIO_MODE_MGMT_STD_INPUT_NOPULL:
Management controls the GPIO pin.
Pin is configured as a digital input, no pull-up or pull-down.
GPIO_MODE_MGMT_STD_INPUT_PULLDOWN:
Management controls the GPIO pin.
Pin is configured as a digital input with a weak (5k) pull-down.
GPIO_MODE_MGMT_STD_INPUT_PULLUP:
Management controls the GPIO pin.
Pin is configured as a digital input with a weak (5k) pull-up.
GPIO_MODE_MGMT_STD_OUTPUT:
Management controls the GPIO pin.
Pin is configured as a digital output (output only).
GPIO_MODE_MGMT_STD_BIDIRECTIONAL:
Management controls the GPIO pin.
Pin is configured as a digital input or output. The direct
control of the GPIO from the management SoC does not include
bidirectional control, and this should only be set for those
special functions that use bidirectional or tristatable pins
(flash QSPI data pins, housekeeping SDO, SPI master SDO, and
the debug pin).
GPIO_MODE_MGMT_STD_ANALOG:
Digital input and output buffers are disabled. The pin has no
function for the management SoC.
GPIO_MODE_USER_STD_INPUT_NOPULL:
The user project controls the GPIO pin.
Pin is configured as a digital input, no pull-up or pull-down.
GPIO_MODE_USER_STD_INPUT_PULLDOWN:
The user project controls the GPIO pin.
Pin is configured as a digital input with a weak (5k) pull-down.
GPIO_MODE_USER_STD_INPUT_PULLUP:
The user project controls the GPIO pin.
Pin is configured as a digital input with a weak (5k) pull-up.
GPIO_MODE_USER_STD_OUTPUT:
The user project controls the GPIO pin.
Pin is configured as a digital output (output only).
GPIO_MODE_USER_STD_BIDIRECTIONAL:
The user project controls the GPIO pin.
Pin is configured as a digital input or output. The input
(io_in) is always active. The output (io_out) is applied to
the pad only if the corresponding output disable (io_oeb) is
set to zero.
GPIO_MODE_USER_STD_OUT_MONITORED:
The user project controls the GPIO pin like
the GPIO_MODE_USER_STD_BIDIRECTIONAL mode, above; however,
the pad value also appears at the management SoC, so the
management SoC can treat this pad as an input pin, monitoring
the value seen by the user project.
GPIO_MODE_USER_STD_ANALOG:
The user project controls the GPIO pin.
Digital input and output buffers are disabled. If the
corresponding analog_io pin is connected to an analog signal
in the user project, then that signal (unbuffered) appears on
the pad.
--------------------------------------------------------------------------
Register name = reg_mprj_xfer
Memory location = 0x26000000
Housekeeping SPI location = 0x13
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x13 | | data | data | clock | load | resetn| enable| xfer/ |
| | | 2 | 1 | | | | | busy |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
bit 0: xfer / busy
On reading this bit:
value 0 = The serial transfer is idle
value 1 = The serial transfer is in progress
On writing this bit:
value 0 = No action (the default state)
value 1 = Initiate a serial transfer of GPIO configuration
data from the housekeeping registers to the GPIOs.
bit 1: Serial bit-bang enable:
value 0 = Serial transfer is done by the "xfer" bit.
value 1 = Serial transfer is done by bit banging.
bit 2: Serial bit-bang reset bar:
value 0 = Reset all GPIO to their default values
value 1 = No action (the default state)
(See also the page on setting the default GPIO configuration.)
bit 3: Serial bit-bang load:
value 0 = No action (the default state)
value 1 = Simultaneously copy all GPIO configuration data
from the shift register to the GPIOs.
bit 4: Serial bit-bang clock:
value 0 = No action (the default state)
value 1 = Advance data in the serial shift registers by 1 bit
bit 5: Serial bit-bang data 1:
value = GPIO configuration for the left side to be shifted on
next clock.
bit 6: Serial bit-bang data 2:
value = GPIO configuration for the right side to be shifted on
next clock.
The GPIO pins are configured through a serial chain that allows the
static configuration setting of each GPIO to be registered close to the
pad and avoid wiring every configuration bit of every pad back to the
management area. The configuration held near the pad is a copy of the
configuration held in the memory mapped registers. The value in the
memory mapped register can be considered a "staging area" value. The
GPIO function will not update until the values are transferred from the
housekeeping registers to the GPIO pad. The function that does this is
the "transfer" bit in this register. The remaining values allow the
serial programming to be done manually by "bit banging". The bit
bang functions should be considered diagnostic only.
In normal (not bit-bang) mode, the "xfer" bit needs to be set to one to
initiate a transfer of data from the memory mapped registers in the
housekeeping module to the GPIOs. The "xfer" bit is self-resetting back
to zero. The value of this bit cannot be read directly. When reading
back this register, the bit 0 position contains the "busy" state of the
serial transfer. This allows the control program for the management SoC
to know when the GPIO pins have been properly configured. The "busy" bit
will be set back to zero after the serial load has occurred.
In "bit-bang" mode, the register is used to directly control the
operation of the serial load instead of the automatic load initiated
by the "xfer" bit. "bit-bang" mode is considered diagnostic, and should
not need to be used. For completeness, its operation is described below:
There are two serial shift registers, one on the left side of the chip
running from mprj_io[37] to mprj_io[19], and the other on the right side
of the chip running from mprj_io[0] to mprj_io[18]. There are 13 bits
per GPIO according to the configuration registers (see above), applied
consecutively and in reverse. So the first value applied to data 2 is
mprj_io[18] configuration bit 12, and the the last value is mprj_io[0]
configuration bit 0, with 19 * 13 = 247 bits total. After applying each
data bit, toggle the clock. At the end of 247 clocks, the load bit is
toggled to transfer the data from the shift register to the GPIOs.
General-purpose I/O standard operation:
----------------------------------------
When a GPIO is configured for management control, and the management SoC
is not using that pin for a special function (see special functions,
below), the GPIO pin may be used for bit-wise read and write operations.
The two registers reg_mprj_datal (32 bits) and reg_mprj_datah (6 bits)
together comprise the data registers for direct readback and control of
the GPIO pad values to and from the management SoC. Unlike the static
configuration setting, these values are connected directly to the GPIOs
and update when written.
Note that the registers reg_mprj_datal and reg_mprj_datah are effectively
write-only. Reading from these addresses reads the bit value of the GPIO
pad, not the value stored in the register. There is no method implemented
to read back the value written to these registers.
--------------------------------------------------------------------------
Register name = reg_mprj_datal
Memory location = 0x2600000c
Housekeeping SPI location = 0x6a to 0x6d
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x6d | gpio | gpio | gpio | gpio | gpio | gpio | gpio | gpio |
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x6c | gpio | gpio | gpio | gpio | gpio | gpio | gpio | gpio |
| | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x6b | gpio | gpio | gpio | gpio | gpio | gpio | gpio | gpio |
| | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x6a | gpio | gpio | gpio | gpio | gpio | gpio | gpio | gpio |
| | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
--------------------------------------------------------------------------
Register name = reg_mprj_datah
Memory location = 0x26000010
Housekeeping SPI location = 0x69
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x69 | | | gpio | gpio | gpio | gpio | gpio | gpio |
| | | | 37 | 36 | 35 | 34 | 33 | 32 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
IMPORTANT NOTE: When writing to the GPIO data from the housekeeping
SPI, all writes are done byte-wise. When writing GPIO data from the
management SoC, the lower word (GPIO 0 to 31) is written simultaneously,
and the upper word (GPIO 32 to 37) is written simultaneously. There is
no option at this time to update all 38 GPIO outputs at the same time.
In particular, note that an 8-bit or 16-bit write to the register from
the management SoC that does not include the upper byte will *not*
update, but will save the written value to a temporary register that
will be applied when the upper byte is written. Therefore it is
recommended to always make 32-bit writes to the reg_mprj_datal register
to avoid unexpected behavior. 8-, 16-, and 32-bit reads on this register
will work as expected.
GPIO under user project control
---------------------------------------------------
When used by the user project, every GPIO is a simple bidirectional digital
pad. The GPIO is configured by the serial transfer method above to behave
as required by the user project. Once configured to user control, the GPIO
can be controlled by three pins:
io_in[37:0]
io_out[37:0]
io_oeb[37:0]
The io_in[..] signals are from the pad to the user project and are always
active unless the pad has been configured with the "input disable" bit set.
The io_out[..] signals are from the user project to the pad.
The io_oeb[..] signals are from the user project to the pad cell. This
controls the direction of the pad when in bidirectional mode. When set to
value zero, the pad direction is output and the value of io_out[..] appears
on the pad. When set to value one, the pad direction is input and the pad
output buffer is disabled.
The exact behavior of these signals depends on the static configuration of
the corresponding GPIO pad. See the predefined user mode definitions,
above.
Dedicated GPIO functions used by the management SoC
---------------------------------------------------
The housekeeping module defines specific GPIOs to be used for special
functions when those GPIOs are under control of the management SoC.
The dual function for each mprj_io pad is as follows:
mprj_io[0] Debug*
mprj_io[1] housekeeping SDO
mprj_io[2] housekeeping SDI
mprj_io[3] housekeeping CSB
mprj_io[4] housekeeping SCK
mprj_io[5] UART ser_rx
mprj_io[6] UART ser_tx
mprj_io[7] IRQ 1 source
mrpj_io[8] user flash CSB
mrpj_io[9] user flash SCK
mrpj_io[10] user flash IO0
mrpj_io[11] user flash IO1
mprj_io[12] IRQ 2 source
mprj_io[13] Trap monitor**
mprj_io[14] Core clock monitor
mprj_io[15] User clock monitor
mprj_io[32] SPI master SCK
mprj_io[33] SPI master CSB
mprj_io[34] SPI master SDI
mprj_io[35] SPI master SDO
mprj_io[36] flash IO2*
mprj_io[37] flash IO3*
*The Debug and flash QSPI modes may not be available on all management SoC
core types.
**The trap signal may not be implemented on all management SoC core types,
and this pin may be connected to a different signal for monitoring, or
none at all.
The 38 GPIO pins are accessed in the following order of precedence:
(1) The user project accesses the GPIO whenever the GPIO configuration
"management enable" bit (bit 0) is set to 0, using the 3-wire
interface (io_in, io_out, io_oeb).
(2) The management SoC accesses the GPIO with a special function when
the GPIO configuration "management enable" bit (bit 0) is set to
1, and the corresponding special function is enabled (see summary
below for the enable bit for each special function).
(3) The management SoC accesses the GPIO with the standard GPIO read/
write data function when the GPIO configuration "management enable"
bit (bit 0) is set to 1, and no special function is enabled.
A summary of each dedicated management core function is provided below:
Debug:
The debug pin enables the debug function on any management SoC core
that supports a debug mode. Its use is open-ended and depends on
the specific core, but a typical use case is that applying a "1"
value to this pin (setting to VDDIO) activates the UART and allows
debugging through the UART port. The debug function is enabled by
the management SoC, and its state is defined by the SoC
implementation. The implementation may choose to set the debug
enable signal high always, in which case the GPIO 0 pin cannot be
used by the management SoC for general-purpose I/O (this does not
affect the use of the pin by the user project).
Housekeeping SPI:
GPIO pads 1-4 are dedicated to the housekeeping SPI on power-up and
may not be configured otherwise by default. This allows a 4-pin
diagnostic SPI interface for querying the project ID of the chip and
a number of the internal memory mapped registers, as well as allowing
access to apply a manual interrupt to the CPU, to manually reset the
chip, or to program the SPI flash with the pass-through mode. On the
demonstration board, these pins are connected directly to the FTDI
chip so that the housekeeping SPI can be read and written from a host
computer through USB. They may be reconfigured for use by the user
project; the FTDI can be configured to tristate these pins so that
the user project can use them unconditionally. Generally speaking,
a user project should use these pins as a "last resort". When a
user project controls these pads, the "housekeeping disable" bit
should be set to 1. Likewise, when the management SoC wants to use
these pins for general-purpose I/O, the "housekeeping disable" bit
should be set to 1. Otherwise the housekeeping SPI pins are always
enabled for the special function.
UART:
GPIO pads 5 and 6 can be used by the management SoC as a serial UART.
When the UART enable bit is set in the UART control register, these
pins are used for UART Tx and Rx. When the UART enable bit is cleared,
these pins are general purpose I/O. Generally, a user project should
try to keep these pins free for use by the management SoC, since the
UART is the most convenient method for communication between the
management SoC and a host computer.
SPI master:
GPIO pads 32 to 35 are the I/O of the SPI master when it is
enabled.
Flash QSPI:
For management SoC architectures that support QSPI mode on the
SPI flash controller, the two highest-numbered GPIOs (36 and 37)
will act as data lines IO2 and IO3 when QSPI mode is enabled
on the flash controller.
Clock monitoring:
The two primary clocks from the Caravel clock module are the
core clock driving the management SoC, and the user clock, which
is a secondary clock available to the user space that is derived
from the upstream clock but with an independent output divider
(see the page on the digital locked loop). The core clock can
be copied to GPIO 14, and the secondary clock can be copied to
GPIO 15 for monitoring. Note that the GPIOs have a bandwidth
limit of 60MHz, and it is possible to run a clock up to about
150MHz. Frequencies higher than 60MHz will be severely
attenuated, although it should be possible to measure them
with a frequency counter.
Trap monitoring:
For management SoC architectures that generate a trap or fault
signal when the CPU fails, the signal can be routed to GPIO 13
for monitoring.
IRQ source:
GPIO pads 7 and 12 can be set to be the source for two IRQ lines
into the management SoC. The specific IRQs used by the management
SoC depends largely on the SoC implementation.
User flash SPI:
GPIO pads 8 to 11 can be used with an alternate pass-through
programming mode if connected to an SPI flash with the pin
assignments shown above. It is recommended that any user project
that has its own SPI flash controller should use these pins, so
that the flash can be programmed directly from a host computer
through the housekeeping SPI interface. Since the pass-through
mode does not use QSPI mode, only four pins are needed for the
pass-through function. If the user project's SPI flash controller
supports quad mode, then the additional two data pins can use
any available GPIO. There is no requirement for the user to
make use of these pins for an SPI flash, but the pass-through
mode is implemented on these pins as a convenience. To use the
pass-through mode, the following must be done:
(1) The GPIO pads 8 to 11 are put under management SoC
control with the "management enable" bit.
(2) The housekeeping SPI pads 1 to 4 must be under
management SoC control.
(3) The houskeeping SPI is enabled.
(4) The housekeeping SPI is given the command to enter
pass-through mode.
In theory, any pins can be set to management control through the
housekeeping SPI and bit-banged, but the dedicated pass-through
mode is much faster and easier to implement since the SPI commands
can be passed straight through a USB connection from a host
computer.
As noted above, some of the special functions are enabled per implementation
of the management SoC (debug, UART, SPI master, flash QSPI). For the
register setting that enable these functions, please see the documentation
for the management SoC. The enables are specified to be placed at the
following locations (but the actual location may be implementation dependent):
UART: 0x20000008 bit 0 = UART enable
SPI master: 0x24000000 bit 13 = SPI master enable
QSPI: 0x2d000000 bit 21 = QSPI enable
The remaining special functions are controlled by the housekeeping module,
and the special function enables are registered as shown below:
--------------------------------------------------------------------------
Register name = reg_hkspi_disable
Memory location = 0x26200010
Housekeeping SPI location = 0x1c
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x1c | | | | | | | |house- |
| | | | | | | | |keeping|
| | | | | | | | |disable|
+------+-------+-------+-------+-------+-------+-------+-------+-------+
bit 0: Housekeeping SPI disable
value 0 = Housekeeping SPI is enabled on GPIO pins 1 to 4
value 1 = Housekeeping SPI is disabled; GPIO pins 1 to 4
are general-purpose I/O.
--------------------------------------------------------------------------
Register name = reg_trap_out_dest, reg_clk_out_dest
Memory location = 0x26200004
Housekeeping SPI location = 0x1b
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x1b | | | | | | clk1 | clk2 | trap |
| | | | | | |monitor|monitor|monitor|
+------+-------+-------+-------+-------+-------+-------+-------+-------+
bit 0: Trap source monitor
value = 0: GPIO pin 13 is general-purpose I/O
value = 1: GPIO pin 13 outputs the CPU trap state, if
available
bit 1: User clock monitor
value = 0: GPIO pin 15 is general-purpose I/O
value = 1: GPIO pin 15 outputs the user clock.
bit 2: Core clock monitor
value = 0: GPIO pin 14 is general-purpose I/O
value = 1: GPIO pin 14 outputs the core clock.
--------------------------------------------------------------------------
Register name = reg_irq_source
Memory location = 0x2620000c
Housekeeping SPI location = 0x1c
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 0x1b | | | | | | | irq 2 | irq 1 |
| | | | | | | | source| source|
+------+-------+-------+-------+-------+-------+-------+-------+-------+
bit 0: IRQ 1 source
value = 0: GPIO pin 7 is general-purpose I/O
value = 1: GPIO pin 7 is an interrupt to the CPU
(the interrupt number is dependent on the
management SoC architecture implementation).
bit 1: IRQ 2 source
value = 0: GPIO pin 12 is general-purpose I/O
value = 1: GPIO pin 12 is an interrupt to the CPU
(the interrupt number is dependent on the
management SoC architecture implementation).