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kernel_print.rst

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Kernel Debug Print

Note

Tools are only fully supported on source builds.

Overview

The device can optionally print to the host terminal or a log file. This feature can be useful for printing variables, addresses, and Circular Buffer data from kernels running on the device. Device-side prints are controlled through API calls; the host-side is controlled through environment variables.

Enabling

Kernel debug printing can be enabled and configured using the environment variables shown below. The first environment variable, TT_METAL_DPRINT_CORES specifies which cores the host-side will read print data from, and whether this environment variable is defined determines whether printing is enabled during kernel compilation. Note that the core coordinates are logical coordinates, so worker cores and ethernet cores both start at (0, 0).

export TT_METAL_DPRINT_CORES=0,0                    # required, x,y OR (x1,y1),(x2,y2),(x3,y3) OR (x1,y1)-(x2,y2) OR all OR worker OR dispatch
export TT_METAL_DPRINT_ETH_CORES=0,0                # optional, x,y OR (x1,y1),(x2,y2),(x3,y3) OR (x1,y1)-(x2,y2) OR all OR worker OR dispatch
export TT_METAL_DPRINT_CHIPS=0                      # optional, comma separated list of chips
export TT_METAL_DPRINT_RISCVS=BR                    # optional, default is all RISCs. Use a subset of BR,NC,TR0,TR1,TR2
export TT_METAL_DPRINT_FILE=log.txt                 # optional, default is to print to the screen
export TT_METAL_DPRINT_PREPEND_DEVICE_CORE_RISC=0   # optional, enabled by default. Prepends prints with <device id>:(<core x>, <core y>):<RISC>:.
export TT_METAL_DPRINT_ONE_FILE_PER_RISC=1          # optional, splits DPRINT data on a per-RISC basis into files under $TT_METAL_HOME/generated/dprint/. Overrides TT_METAL_DPRINT_FILE and disables TT_METAL_DPRINT_PREPEND_DEVICE_CORE_RISC.

To generate kernel debug prints on the device, include the debug/dprint.h header and use the APIs defined there. An example with the different features available is shown below:

#include "debug/dprint.h"  // required in all kernels using DPRINT

void kernel_main() {
    // Direct printing is supported for const char*/char/uint32_t/float
    DPRINT << "Test string" << 'a' << 5 << 0.123456f << ENDL();
    // BF16 type printing is supported via a macro
    uint16_t my_bf16_val = 0x3dfb; // Equivalent to 0.122559
    DPRINT << BF16(my_bf16_val) << ENDL();

    // dprint.h includes macros for a subset of std::ios and std::iomanip functionality:
    // SETPRECISION macro has the same behaviour as std::setprecision
    DPRINT << SETPRECISION(5) << 0.123456f << ENDL();
    // FIXED and DEFAULTFLOAT macros have the same behaviour as std::fixed and std::defaultfloat
    DPRINT << FIXED() << 0.123456f << DEFAULTFLOAT() << 0.123456f << ENDL();
    // SETW macro is the same as std::setw, but with an optional sticky flag (default true)
    DPRINT << "SETW (sticky): " << SETW(10) << 1 << 2 << ENDL();
    DPRINT << "SETW (non-sticky): " << SETW(10, false) << 1 << 2 << ENDL();
    // HEX/DEC/OCT macros corresponding to std::hex/std::dec/std::oct
    DPRINT << HEX() << 15 << DEC() << 15 << OCT() << 15 << ENDL();

    // The following prints only occur on a particular RISCV core:
    DPRINT_MATH(DPRINT << "this is the math kernel" << ENDL());
    DPRINT_PACK(DPRINT << "this is the pack kernel" << ENDL());
    DPRINT_UNPACK(DPRINT << "this is the unpack kernel" << ENDL());
    DPRINT_DATA0(DPRINT << "this is the data movement kernel on noc 0" << ENDL());
    DPRINT_DATA1(DPRINT << "this is the data movement kernel on noc 1" << ENDL());
}

Data from Circular Buffers can be printed using the TileSlice object. It can be constructed as described below, and fed directly to a DPRINT call.

Argument Type Description
cb_id uint8_t Id of the Circular Buffer to print data form.
tile_idx int Index of tile inside the CB to print data from.
slice_range SliceRange A struct to describe starting index, ending index, and stride for data to print within the CB. Fields are h0, h1, hs, w0, w1, ws, all uint8_t.
cb_type dprint_tslice_cb_t Only used for Data Movement RISCs, specify TSLICE_INPUT_CB or TSLICE_OUTPUT_CB depending on if the CB to print from is input or output.
ptr_type dprint_tslice_ptr_t Only used for Data Movement RISCs, specify TSLICE_RD_PTR to read from the front of the CB, or TSLICE_WR_PTR to read from the back of the CB. UNPACK RISC only reads from the front of the CB, PACK RISC only reads from the back of the CB.
endl_rows bool Whether to add a newline between printed rows, default true.
print_untilized bool Whether to untilize the CB data while printing it (always done for block float formats), default true.

An example of how to print data from a CB (in this case, CBIndex::c_25) is shown below. Note that sampling happens relative to the current CB read or write pointer. This means that for printing a tile read from the front of the CB, the DPRINT call has to occur between the cb_wait_front and cb_pop_front calls. For printing a tile from the back of the CB, the DPRINT call has to occur between the cb_reserve_back and cb_push_back calls. Currently supported data formats for printing from CBs are DataFormat::Float32, DataFormat::Float16_b, DataFormat::Bfp8_b, and DataFormat::Bfp4_b.

#include "debug/dprint.h"  // required in all kernels using DPRINT

void kernel_main() {
    // Assuming the tile we want to print from CBIndex::c_25 is from the front the CB, print must happen after
    // this call. If the tile is from the back of the CB, then print must happen after cb_reserve_back().
    cb_wait_front(CBIndex::c_25, 1);
    ...

    // Extract a numpy slice `[0:32:16, 0:32:16]` from tile `0` from `CBIndex::c_25` and print it.
    DPRINT << TSLICE(CBIndex::c_25, 0, SliceRange::hw0_32_16()) << ENDL();
    // Note that since the MATH core does not have access to CBs, so this is an invalid print:
    DPRINT_MATH({ DPRINT  << TSLICE(CBIndex::c_25, 0, SliceRange::hw0_32_16()) << ENDL(); }); // Invalid

    // Print a full tile
    for (int32_t r = 0; r < 32; ++r) {
        SliceRange sr = SliceRange{.h0 = r, .h1 = r+1, .hs = 1, .w0 = 0, .w1 = 32, .ws = 1};
        // On data movement RISCs, tiles can be printed from either the CB read or write pointers. Also need to specify whether
        // the CB is input or output.
        DPRINT_DATA0({ DPRINT << (uint)r << " --READ--cin1-- " << TileSlice(0, 0, sr, TSLICE_INPUT_CB, TSLICE_RD_PTR, true, false) << ENDL(); });
        DPRINT_DATA1({ DPRINT << (uint)r << " --READ--cin1-- " << TileSlice(0, 0, sr, TSLICE_OUTPUT_CB, TSLICE_WR_PTR, true, false) << ENDL(); });
        // Unpacker RISC only has rd_ptr and only input CBs, so no extra args
        DPRINT_UNPACK({ DPRINT << (uint)r << " --READ--cin1-- " << TileSlice(0, 0, sr, true, false) << ENDL(); });
        // Packer RISC only has wr_ptr
        DPRINT_PACK({ DPRINT << (uint)r << " --READ--cin1-- " << TileSlice(0, 0, sr, true, false) << ENDL(); });
    }

    ...
    cb_pop_front(CBIndex::c_25, 1);
}

Note

The DPRINT buffer for a RISC is only flushed when ENDL() is called, a \n character is read, or the device that the RISC belongs to is closed.