If the CPU is resetting during a Wishbone transfer, assert the ERR line.
Because the resetOut line is likely multiple cycles long, this should
give Wishbone enough time to finish its transfer, which will cause d.stb
and i.stb to go to 0, which will return d_err and i_err to 0.
Signed-off-by: Sean Cross <sean@xobs.io>
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>
The REFRESH register accepts an 8-bit address and determines which
register to refresh. Since there are only two addresses currently in
use, this register can be either 0x00 or 0x04.
A refactor replaced the compare with one that checked for any 0 bits.
Since both 0x00 and 0x04 have 0 bits, this check always evaluated as
true, causing the logic to always refresh the CORE register.
Replace this check with an explicit check for 0x00.
Signed-off-by: Sean Cross <sean@xobs.io>
Add support for debugging the CPU, and gate it behind a new cpu_debug
parameter. With this enabled, a simple Wishbone interface is provided.
The debug version of the core adds two 32-bit registers to the CPU.
The register at address 0 indicates status, and is used to halt
and reset the core.
The debug register at address 4 is used to inject opcodes into the
core, and read back the result.
A patched version of OpenOCD can be used to attach to this bus via
the Litex Ethernet or UART bridges.
Signed-off-by: Sean Cross <sean@xobs.io>
The upstream vexriscv repo now generates both the current VexRiscv.v
softcore, as well as VexRiscv-Debug.v. This -Debug varient exposes
their specialized debug bus that allows for attaching a modified version
of openocd.
Sync the litex repo with the upstream version to take advantage of debug
support.
Signed-off-by: Sean Cross <sean@xobs.io>
