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RISC-V hart selection

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2023-11-23 12:56:26 +00:00
parent c4dc3c89f5
commit c1c9a0ceeb
3 changed files with 63 additions and 3 deletions
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56
src/Targets/RiscV/RiscV.cpp
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@@ -30,7 +30,21 @@ namespace Targets::RiscV
void RiscV::activate() {
this->riscVDebugInterface->activate({});
// TODO: Select a hart here.
this->discoverHartIndices();
Logger::debug("Discovered RISC-V harts: " + std::to_string(this->hartIndices.size()));
/*
* We only support MCUs with a single hart, for now. So select the first index and ensure that this is
* explicitly communicated to the user.
*/
if (this->hartIndices.size() > 1) {
Logger::warning(
"Bloom only supports debugging a single RISC-V hart - selecting first available hart"
);
}
this->selectedHartIndex = *(this->hartIndices.begin());
Logger::info("Selected RISC-V hart index: " + std::to_string(this->selectedHartIndex));
this->stop();
}
@@ -65,6 +79,7 @@ namespace Targets::RiscV
void RiscV::run(std::optional<TargetMemoryAddress> toAddress) {
auto controlRegister = ControlRegister();
controlRegister.debugModuleActive = true;
controlRegister.selectedHartIndex = this->selectedHartIndex;
controlRegister.resumeRequest = true;
this->writeControlRegister(controlRegister);
@@ -88,6 +103,7 @@ namespace Targets::RiscV
void RiscV::stop() {
auto controlRegister = ControlRegister();
controlRegister.debugModuleActive = true;
controlRegister.selectedHartIndex = this->selectedHartIndex;
controlRegister.haltRequest = true;
this->writeControlRegister(controlRegister);
@@ -204,6 +220,44 @@ namespace Targets::RiscV
return false;
}
void RiscV::discoverHartIndices() {
/*
* We can obtain the maximum hart index by setting all of the hartsel bits in the control register and then
* reading the value back.
*/
auto controlRegister = ControlRegister();
controlRegister.debugModuleActive = true;
controlRegister.selectedHartIndex = 0xFFFFF;
this->writeControlRegister(controlRegister);
controlRegister = this->readControlRegister();
for (DebugModule::HartIndex hartIndex = 0; hartIndex <= controlRegister.selectedHartIndex; ++hartIndex) {
/*
* We can't just assume that everything between 0 and the maximum hart index are valid hart indices. We
* have to test each index until we find one that is non-existent.
*/
controlRegister = ControlRegister();
controlRegister.debugModuleActive = true;
controlRegister.selectedHartIndex = hartIndex;
this->writeControlRegister(controlRegister);
/*
* It's worth noting that some RISC-V targets **do not** set the non-existent flags. I'm not sure why.
* Have they just hardwired hartsel to 0 because they only support a single hart, preventing the selection
* of non-existent harts?
*
* Relying on the maximum hart index seems to be all we can do in this case.
*/
if (this->readStatusRegister().anyNonExistent) {
break;
}
this->hartIndices.insert(hartIndex);
}
}
ControlRegister RiscV::readControlRegister() {
return ControlRegister(
this->riscVDebugInterface->readDebugModuleRegister(RegisterAddresses::CONTROL_REGISTER)