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vexriscv: put debug bus directly on wishbone bus 

By placing the VexRiscv debug bus on the Wishbone bus, the Etherbone
core can access 32-bit values directly from the core.  Additionally,
both reading and writing are supported without the need to do a SYNC
register as before.

Additionally, the address of the Wishbone bus won't move around anymore,
as it's fixed when doing `self.register_mem()`.

Signed-off-by: Sean Cross <sean@xobs.io>
This commit is contained in:
Sean Cross 2018-07-19 17:47:28 +08:00
parent 20d6fcac61
commit c87ca4f1c3
1 changed files with 53 additions and 130 deletions
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183
litex/soc/cores/cpu/vexriscv/core.py
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@ -5,7 +5,6 @@ from migen import *
from litex.soc.interconnect import wishbone
from litex.soc.interconnect.csr import AutoCSR, CSRStatus, CSRStorage
class VexRiscv(Module, AutoCSR):
def __init__(self, platform, cpu_reset_address, variant=None):
assert variant in (None, "debug"), "Unsupported variant %s" % variant
@ -25,147 +24,71 @@ class VexRiscv(Module, AutoCSR):
cpu_reset = Signal()
cpu_args = {}
cpu_filename = "VexRiscv-Debug.v"
# Create four debug registers:
# DEBUG_CORE: The contents of the debug core register
# DEBUG_DATA: Write an instruction into the pipeline, or read the result.
# DEBUG_REFRESH: Write 0x00 or 0x04 here to update either CORE or DATA
# DEBUG_COUNT: An incrementing value that can be used to detect packet loss.
# Updated on a successful WRITE to CORE, DATA, or REFRESH.
self.debug_core = debug_core = CSRStorage(32, name="debug_core", write_from_dev=True)
self.debug_data = debug_data = CSRStorage(32, name="debug_data", write_from_dev=True)
self.debug_refresh = debug_refresh = CSRStorage(8, name="debug_refresh")
self.debug_counter = debug_counter = CSRStatus(32, name="debug_counter")
# # #
debug_bus_cmd_payload_wr = Signal()
debug_bus_cmd_payload_address = Signal(8)
debug_bus_cmd_payload_data = Signal(32)
debug_bus_cmd_ready = Signal()
debug_bus_rsp_data = Signal(32)
debug_start_cmd = Signal()
debug_update_pending = Signal()
debug_write_pending = Signal()
debug_reset_out = Signal()
debug_reset_counter = Signal(16)
self.i_cmd_valid = Signal()
self.i_cmd_payload_wr = Signal()
self.i_cmd_payload_address = Signal(8)
self.i_cmd_payload_data = Signal(32)
self.o_cmd_ready = Signal()
self.o_rsp_data = Signal(32)
self.o_resetOut = Signal()
# A bit to indicate whether we're REFRESHing the CORE or DATA register
refreshing_data = Signal()
self.transfer_complete = Signal()
self.transfer_in_progress = Signal()
self.transfer_wait_for_ack = Signal()
self.debug_bus = wishbone.Interface()
self.sync += [
# If the core asserts reset_out, set debug_reset for 2**16 cycles.
If(debug_reset_out,
debug_reset_counter.eq(0),
self.debug_reset.eq(1)
).Elif(debug_reset_counter != (2**16-1),
debug_reset_counter.eq(debug_reset_counter + 1)
).Else(
self.debug_reset.eq(0)
),
self.debug_bus.dat_r.eq(self.o_rsp_data),
]
# Reset the CPU if debug_reset is asserted and none of the
# Wishbone buses are in use
cpu_reset.eq((~i.cyc & ~d.cyc & ~d.stb & ~i.stb &
self.debug_reset) | ResetSignal()),
# If there's a Wishbone write on the CORE register, write to
# debug register address 0.
If(debug_core.re,
debug_bus_cmd_payload_address.eq(0x00),
debug_bus_cmd_payload_data.eq(debug_core.storage),
debug_bus_cmd_payload_wr.eq(1),
debug_start_cmd.eq(1),
debug_write_pending.eq(1),
debug_core.we.eq(0),
debug_data.we.eq(0)
# Or, if there's a write to the DATA register, write to
# debug register address 4.
).Elif(debug_data.re,
debug_bus_cmd_payload_address.eq(0x04),
debug_bus_cmd_payload_data.eq(debug_data.storage),
debug_bus_cmd_payload_wr.eq(1),
debug_start_cmd.eq(1),
debug_write_pending.eq(1),
debug_core.we.eq(0),
debug_data.we.eq(0)
# A write to the REFRESH register indicates which register
# (DATA or CORE) we want to update from the CPU.
).Elif(debug_refresh.re,
If(debug_refresh.storage == 0,
refreshing_data.eq(0),
debug_bus_cmd_payload_address.eq(0)
).Else(
refreshing_data.eq(1),
debug_bus_cmd_payload_address.eq(4)
),
# Data can be anything, since it's a "read"
debug_bus_cmd_payload_data.eq(0),
# Start a "Read" command with the "Write" bit set to 0
debug_bus_cmd_payload_wr.eq(0),
debug_start_cmd.eq(1),
# The data will be ready when debug_bus_cmd_ready == 1,
# so set the pending bit to look for it on future cycles.
debug_update_pending.eq(1),
debug_core.we.eq(0),
debug_data.we.eq(0)
# If the pending bit is set, check to see if the cmd_ready
# bit from the debug bus is 1, indicating the CPU has finished
# its operation and is in the idle state.
).Elif(debug_update_pending,
If(debug_bus_cmd_ready,
debug_bus_cmd_payload_wr.eq(0),
debug_update_pending.eq(0),
debug_write_pending.eq(0),
debug_start_cmd.eq(0),
debug_counter.status.eq(debug_counter.status + 1),
# Depending on whether we were asked to update the CORE
# or DATA register, copy the response data to the correct CSR.
If(~refreshing_data,
debug_core.dat_w.eq(debug_bus_rsp_data),
debug_core.we.eq(1),
debug_data.we.eq(0)
).Else(
debug_data.dat_w.eq(debug_bus_rsp_data),
debug_core.we.eq(0),
debug_data.we.eq(1)
self.sync += [
# CYC is held high for the duration of the transfer.
# STB is kept high when the transfer finishes (write)
# or the master is waiting for data (read), and stays
# there until ACK, ERR, or RTY are asserted.
If((self.debug_bus.stb & self.debug_bus.cyc)
& (~self.transfer_in_progress)
& (~self.transfer_complete)
& (~self.transfer_wait_for_ack),
self.i_cmd_payload_data.eq(self.debug_bus.dat_w),
self.i_cmd_payload_address.eq((self.debug_bus.adr[0:6] << 2) | 0),
self.i_cmd_payload_wr.eq(self.debug_bus.we),
self.i_cmd_valid.eq(1),
self.transfer_in_progress.eq(1),
self.transfer_complete.eq(0),
self.debug_bus.ack.eq(0)
).Elif(self.transfer_in_progress,
If(self.o_cmd_ready,
self.i_cmd_valid.eq(0),
self.i_cmd_payload_wr.eq(0),
self.transfer_complete.eq(1),
self.transfer_in_progress.eq(0)
)
)
# If there's a pending write to CORE or DATA, increment the
# packet counter once the operation has finished.
).Elif(debug_write_pending,
If(debug_bus_cmd_ready,
# When debug_bus_cmd_ready goes 1,
debug_counter.status.eq(debug_counter.status + 1),
debug_update_pending.eq(0),
debug_write_pending.eq(0),
debug_start_cmd.eq(0),
debug_data.we.eq(0),
debug_core.we.eq(0)
)
# Otherwise, ensure the Write Enable bits on the registers
# are 0, so we're not constantly loading floating values.
).Else(
debug_core.we.eq(0),
debug_data.we.eq(0)
).Elif(self.transfer_complete,
self.transfer_complete.eq(0),
self.debug_bus.ack.eq(1),
self.transfer_wait_for_ack.eq(1)
).Elif(self.transfer_wait_for_ack & ~(self.debug_bus.stb & self.debug_bus.cyc),
self.transfer_wait_for_ack.eq(0),
self.debug_bus.ack.eq(0)
)
]
cpu_reset.eq((~i.cyc & ~d.cyc & ~d.stb & ~i.stb &
self.o_resetOut) | ResetSignal()),
cpu_args.update({
"i_debugReset": ResetSignal(),
"i_debug_bus_cmd_valid": debug_start_cmd,
"i_debug_bus_cmd_payload_wr": debug_bus_cmd_payload_wr,
"i_debug_bus_cmd_payload_address": debug_bus_cmd_payload_address,
"i_debug_bus_cmd_payload_data": debug_bus_cmd_payload_data,
"o_debug_bus_cmd_ready": debug_bus_cmd_ready,
"o_debug_bus_rsp_data": debug_bus_rsp_data,
"o_debug_resetOut": debug_reset_out
"i_debug_bus_cmd_valid": self.i_cmd_valid,
"i_debug_bus_cmd_payload_wr": self.i_cmd_payload_wr,
"i_debug_bus_cmd_payload_address": self.i_cmd_payload_address,
"i_debug_bus_cmd_payload_data": self.i_cmd_payload_data,
"o_debug_bus_cmd_ready": self.o_cmd_ready,
"o_debug_bus_rsp_data": self.o_rsp_data,
"o_debug_resetOut": self.o_resetOut
})
self.specials += Instance("VexRiscv",