The design is backward-compatible in functionality for users
who don't want to use DRP. That is, on power on, the XADC will
scan the supply and temperature and store them in CSRs.
If drp_enable is set, the scanning stops, and the XADC is now
controlled by the DRP bus.
Wher drp_enable is reset, the XADC may return to an auto-sample
mode, but only if the internal registers are configured to do this.
If you return to drp_enable without, for example, turning on
the continuous sequence and setting which channels to check,
the results will be unpredictable (mostly either it'll scan just
once and stop, or it'll not scan all the channels, depending on
the register settings).
At this point, the backward compatibility was confirmed in testing,
the DRP API is still a work in progress as the application this
is being developed for needs to support fun stuff like real time
sampling of signals to a buffer.
Down the road, this block may have to be modified again to support an
output FIFO, so we're not railing the CPU trying to do real time
sampling of ADC data. This will probably be added as a True/False flag
of some sort in the parameter list, because the FIFO will be expensive
as far as BRAM goes to implement and applications that don't need the
FIFO buffer can probably use that BRAM for better things.
If clocks and multipliers are planned well, we can have
a zero-error solution for clocks. Suggest to change < to <= in
margin comparison loop, so that a "perfect" solution is allowed
to converge.
Various development boards' LiteDRAM ports may have native data
widths of either 64 (nexys4ddr), 128 (versa5g), or 256 (trellis)
bits. Add Rocket variants configured with mem_axi ports of matching
data widths, so that a point to point connection between the CPU's
memory port and LiteDRAM can be accomplished without any additional
data width conversion gateware.
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Enforce the condition that csr_alignment be either 32 or 64 when
requested explicitly when initializing SoCCore().
Additionally, if a CPU is specified, enforce that csr_alignment be
equal to the native CPU word size (currently either 32 or 64), and
warn the caller if an alignment value *higher* than the CPU native
word size was explicitly requested.
In conclusion, if a CPU is specified, then csr_alignment should be
assumed to equal 8*sizeof(unsigned long).
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Since the PLIC is internal to Rocket, access its registers
directly via pointer dereference, rather than through the
LiteX CSR Bus accessors (which assume subregister slicing,
and are therefore inappropriate for registers NOT accessed
over the LiteX CSR Bus).
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Since csr_data_width=64 has probably never worked properly, remove
it as one of the possible options (to be fixed and re-added later).
Add csr_data_width=16, which has been tested and does work.
Additionally, ensure csr_data_width <= csr_alignment (we should not
attempt to create (sub)registers larger than the CPU's native word
size or XLen).
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
bunnie
Florent Kermarrec
Tim 'mithro' Ansell
Giammarco Zacheo
Gabriel Somlo
Arnaud Durand