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A quick documentation of the Caravel memory map and operation
Caravel pinout:
vddio 3.3V supply for all I/O and ESD
vssio Ground for all I/O and ESD
vdda 3.3V supply for management area
vssa Ground for management area
vccd 1.8V supply for management area
vssd Digital ground for management area
vdda1 3.3V supply for user area 1
vdda2 3.3V supply for user area 2
vssa1 Ground for user area 1
vssa2 Ground for user area 2
vccd1 1.8 supply for user area 1
vccd2 1.8 supply for user area 2
vssd1 Digital ground for user area 1
vssd2 Digital ground for user area 2
clock Master clock input
gpio 1 bit, mainly used for external LDO control of user power supply
mprj_io 32 bits general purpose programmable digital or analog I/O
resetb Master reset (sense inverted) input
flash_csb SPI flash controller chip select (sense inverted)
flash_clk SPI flash controller clock
flash_io0 SPI flash controller data out
flash_io1 SPI flash controller data in
Special-use pins for the management SoC:
On power-up, the "mprj_io" GPIO are under complete control of the managment
SoC. The first 8 user GPIO are special-purpose pads with dedicated functions
for the management SoC:
mprj_io[0] JTAG I/O
mprj_io[1] SDO, housekeeping SPI
mprj_io[2] SDI, housekeeping SPI
mprj_io[3] CSB, housekeeping SPI
mprj_io[4] SCK, housekeeping SPI
mprj_io[5] Rx, UART
mprj_io[6] Tx, UART
mprj_io[7] IRQ
The next 4 user GPIO are designed to be used with an SPI flash controller in
the user space. They allow the four pins to be overridden by the housekeeping
SPI to access the SPI flash in pass-through mode.
mprj_io[8] user flash CSB
mprj_io[9] user flash SCK
mprj_io[10] user flash IO0
mprj_io[11] user flash IO1
The user may additionally use any available GPIO for the SPI flash IO2 and IO3
lines; the pass-through mode only uses the basic 4-pin SPI mode.
All of the special-use pins are configured through a memory-mapped region. But
to avoid a large number of wires in the user space to reach all of the GPIO
pad controls, each user GPIO pad has a corresponding local control block. The
control block holds the configuration data for the corresponding pad. This
configuration data is a mirror of the data in the memory-mapped region, and is
loaded by a "transfer" bit in another memory-mapped register. In addition to
all of the static control bits for the GPIO, each block contains a single bit
that specifies whether that pad is under the control of the user or the management
area. All pins are configured from the management area. However, the configuration
of static control bits leaves three dynamic signals: input, output, and output
enable. One set of these three signals is available to the user when the pad is
under user control. The other set of these three signals is available to the
management SoC. Again, to reduce wiring, only the two pads for JTAG and the
housekeeping SDO have all three pins under control of the SoC; the remaining
pads have a single wire to the management SoC which is either an input wire
or an output wire, depending on how the control signals for the pad are set.
This setup gives a simplified view of the pad to the user: For digital
applications, the user can treat the pad as a simple bidirectional digital
pad with an output enable to switch between output and input functions.
The user can set the output enable line high or low for a static input or
output function. The user will also have access to the ESD-protected
pad connections for analog signals, and can connect to the VDDA domain
input digital signal if needed.
Memory map:
The Caravel memory map is as follows:
SRAM: 0000 0000
Flash: Config: 1000 0000
UART: Clock divider: 2000 0000
Data: 2000 0004
Enable 2000 0008
GPIO: Data: 2100 0000
Output enable: 2100 0004
Pullup 2100 0008
Pulldown 2100 000c
Counter 1: Config: 2200 0000
Value: 2200 0004
Data: 2200 0008
Counter 2: Config: 2300 0000
Value: 2300 0004
Data: 2300 0008
SPI master: Config: 2400 0000
Data: 2400 0004
Logic analyzer: Data 0: 2500 0000
Data 1: 2500 0004
Data 2: 2500 0008
Data 3: 2500 000c
Enable 0: 2500 0010
Enable 1: 2500 0014
Enable 2: 2500 0018
Enable 3: 2500 001c
Project ctrl: Data (L): 2600 0000
Data (H): 2600 0004
Transfer: 2600 0008
I/O Config: 2600 000c
to 2600 009c
Power Config: 2600 00a0
to 2600 0130
Flash ctrl: Config: 2D00 0000
System: PLL out: 2F00 0000
Trap out: 2F00 0004
IRQ7 source: 2F00 0008
User area base: 3000 0000
Crossbar: QSPI control 8000 0000
Storage area 9000 0000
Any slave 1 a000 0000
Any slave 2 b000 0000
Project I/O Control:
Configuration bits per I/O (13 bits for each GPIO pad):
Global Default
Bits 12-10: digital mode (3 bits) 001
Bit 9: voltage trip point select 0
Bit 8: slow slew select 0
Bit 7: analog bus polarity 0
Bit 6: analog bus select 0
Bit 5: analog bus enable 0
Bit 4: IB mode select 0
Bit 3: input disable 0
Bit 2: holdover value 0
Bit 1: output disable 1
Bit 0: management control enable 1
Default I/O modes:
mprj_io[0] JTAG I/O 110 0 0 0 0 0 0 0 0 0 1
mprj_io[1] SDO, housekeeping SPI 110 0 0 0 0 0 0 0 0 0 1
all others: 001 0 0 0 0 0 0 0 0 1 1
Standard GPIO output configuration:
mprj_io[6] Tx, UART 110 0 0 0 0 0 0 1 0 0 1
Standard GPIO input configuration:
mprj_io[*] 001 0 0 0 0 0 0 0 0 1 1
Standard GPIO input configuration with pullup:
mprj_io[*] 010 0 0 0 0 0 0 0 0 1 1
Standard GPIO input configuration with pulldown:
mprj_io[*] 011 0 0 0 0 0 0 0 0 1 1
JTAG and SDO are set to output. The output enable configure bit
is a don't-care, since the output enable line is directly controlled
by the module (JTAG or housekeeping SPI, respectively).
All other I/O are set as input mode only, with output disabled.
Tx is set to input like the others; before enabling the UART
from a program in flash, the I/O must be set to an output configuration.
Note that the standard input configurations with pull-up and pull-down
require that "out" be set 1 or 0, respectively; since the I/O are
designed with minimal wiring, there is only one wire for input and
output, so the wire is used for input in these cases, and special
signal handling is done locally to set the value of "out" equal to
~dm[0]. This is a (minor) restriction on the available I/O modes.
Other possible modes are open-drain (for I2C), weak drive strength
output (5k up + down), and analog mode (digital disabled)