Skip to content

SPIDecoder: Add CPHA and LSB/MSB option #1105

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
dj-bauer wants to merge 2 commits into
base: master
Choose a base branch
from
Open

SPIDecoder: Add CPHA and LSB/MSB option #1105

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
559b433
SPIDecoder: Add CPHA and LSB/MSB option
dj-bauer Aug 9, 2026
0a3f6ce
Merge branch 'ngscopeclient:master' into master
dj-bauer Aug 10, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
115 changes: 71 additions & 44 deletions scopeprotocols/SPIDecoder.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,8 @@ using namespace std;
SPIDecoder::SPIDecoder(const string& color)
: Filter(color, CAT_BUS)
, m_cpol(m_parameters["Clock Polarity"])
, m_cpha(m_parameters["Clock Phase Alignment"])
, m_bendian(m_parameters["Byte Endianness"])
{
AddProtocolStream("data");
CreateInput<InputConstraintStreamType>("clk", Stream::STREAM_TYPE_DIGITAL);
Expand All @@ -55,6 +57,16 @@ SPIDecoder::SPIDecoder(const string& color)
m_cpol.AddEnumValue("Idle low", 0);
m_cpol.AddEnumValue("Idle high", 1);
m_cpol.SetIntVal(0);

m_cpha = FilterParameter(FilterParameter::TYPE_ENUM, Unit(Unit::UNIT_COUNTS));
m_cpha.AddEnumValue("Sample Rising CLK", 0);
m_cpha.AddEnumValue("Sample Falling CLK", 1);
m_cpha.SetIntVal(0);

m_bendian = FilterParameter(FilterParameter::TYPE_ENUM, Unit(Unit::UNIT_COUNTS));
m_bendian.AddEnumValue("LSB First", 0);
m_bendian.AddEnumValue("MSB First", 1);
m_bendian.SetIntVal(1);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
Expand All @@ -66,8 +78,57 @@ string SPIDecoder::GetProtocolName()
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Actual decoder logic

// Sample the current data-bit.
void SPIDecoder::sampleBit(SPIWaveform* cap, size_t timestamp, int endian, uint8_t& current_byte, uint8_t& bitcount, int64_t& bytestart,
bool cur_data, bool first)
{
if(bitcount == 0)
{
//Add a "chip selected" event
if(first)
{
cap->m_offsets.push_back(bytestart);
cap->m_durations.push_back(timestamp - bytestart);
cap->m_samples.push_back(SPISymbol(SPISymbol::TYPE_SELECT, 0));
first = false;
}

//Extend the last byte until this edge
else if(!cap->m_samples.empty())
{
size_t ilast = cap->m_samples.size()-1;
if(cap->m_samples[ilast].m_stype == SPISymbol::TYPE_DATA)
cap->m_durations[ilast] = timestamp- cap->m_offsets[ilast];
}

bytestart = timestamp;
}

if(endian == 0) { // LSB
if(cur_data)
current_byte = (1 << bitcount) | current_byte;
} else { // MSB
if(cur_data)
current_byte = 1 | (current_byte << 1);
else
current_byte = (current_byte << 1);
}
bitcount ++;

if(bitcount == 8)
{
cap->m_offsets.push_back(bytestart);
cap->m_durations.push_back(timestamp - bytestart);
cap->m_samples.push_back(SPISymbol(SPISymbol::TYPE_DATA, current_byte));

bitcount = 0;
current_byte = 0;
bytestart = timestamp;
}
}

// Actual decoder logic
void SPIDecoder::Refresh(
[[maybe_unused]] vk::raii::CommandBuffer& cmdBuf,
[[maybe_unused]] shared_ptr<QueueHandle> queue
Expand Down Expand Up @@ -107,8 +168,6 @@ void SPIDecoder::Refresh(
cap->m_triggerPhase = 0;
cap->PrepareForCpuAccess();

//TODO: different cpha/cpol modes

//TODO: packets based on CS# pulses?

//Loop over the data and look for transactions
Expand Down Expand Up @@ -137,6 +196,9 @@ void SPIDecoder::Refresh(

//Get SPI clock polarity
auto cpol = m_cpol.GetIntVal();
auto cpha = m_cpha.GetIntVal();
// LSB/MSB for data
auto endian = m_bendian.GetIntVal();

bool active_clk;
if(cpol == 0)
Expand Down Expand Up @@ -175,47 +237,9 @@ void SPIDecoder::Refresh(
case STATE_SELECTED_CLK_INACTIVE:
if(cur_clk == active_clk)
{
if(bitcount == 0)
{
//Add a "chip selected" event
if(first)
{
cap->m_offsets.push_back(bytestart);
cap->m_durations.push_back(timestamp - bytestart);
cap->m_samples.push_back(SPISymbol(SPISymbol::TYPE_SELECT, 0));
first = false;
}

//Extend the last byte until this edge
else if(!cap->m_samples.empty())
{
size_t ilast = cap->m_samples.size()-1;
if(cap->m_samples[ilast].m_stype == SPISymbol::TYPE_DATA)
cap->m_durations[ilast] = timestamp - cap->m_offsets[ilast];
}

bytestart = timestamp;
}

if(cpha == 0)
sampleBit(cap, timestamp, endian, current_byte, bitcount, bytestart, cur_data, first);
state = STATE_SELECTED_CLK_ACTIVE;

//TODO: selectable msb/lsb first direction
bitcount ++;
if(cur_data)
current_byte = 1 | (current_byte << 1);
else
current_byte = (current_byte << 1);

if(bitcount == 8)
{
cap->m_offsets.push_back(bytestart);
cap->m_durations.push_back(timestamp - bytestart);
cap->m_samples.push_back(SPISymbol(SPISymbol::TYPE_DATA, current_byte));

bitcount = 0;
current_byte = 0;
bytestart = timestamp;
}
}

//end of packet
Expand All @@ -233,8 +257,11 @@ void SPIDecoder::Refresh(

//wait for falling edge of clk
case STATE_SELECTED_CLK_ACTIVE:
if(cur_clk != active_clk)
if(cur_clk != active_clk) {
if(cpha == 1)
sampleBit(cap, timestamp, endian, current_byte, bitcount, bytestart, cur_data, first);
state = STATE_SELECTED_CLK_INACTIVE;
}

//end of packet
//TODO: error if a byte is truncated
Expand Down
5 changes: 5 additions & 0 deletions scopeprotocols/SPIDecoder.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,11 @@ class SPIDecoder : public Filter

protected:
FilterParameter& m_cpol;
FilterParameter& m_cpha;
// Bit endianess
FilterParameter& m_bendian;
void sampleBit(SPIWaveform*, size_t timestamp, int endian, uint8_t& current_byte, uint8_t& bitcount, int64_t& bytestart,
bool cur_data, bool first);
};

#endif