diff --git a/tools/pioasm/pio_assembler.cpp b/tools/pioasm/pio_assembler.cpp
new file mode 100644
index 0000000..469d733
--- /dev/null
+++ b/tools/pioasm/pio_assembler.cpp
@@ -0,0 +1,390 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <cstdio>
+#include <iterator>
+#include "pio_assembler.h"
+#include "parser.hpp"
+
+#ifdef _MSC_VER
+#pragma warning(disable : 4996) // fopen
+#endif
+
+using syntax_error = yy::parser::syntax_error;
+
+std::string output_format::default_name = "c-sdk";
+
+pio_assembler::pio_assembler() {
+}
+
+int pio_assembler::generate(std::shared_ptr<output_format> _format, const std::string &_source,
+                            const std::string &_dest, const std::vector<std::string> &_options) {
+    format = _format;
+    source = _source;
+    dest = _dest;
+    options = _options;
+    location.initialize(&source);
+    scan_begin();
+    yy::parser parse(*this);
+//    parse.set_debug_level(false);
+    int res = parse();
+    scan_end();
+    return res;
+}
+
+void program::add_instruction(std::shared_ptr<instruction> inst) {
+    uint limit = MAX_INSTRUCTIONS;
+    if (instructions.size() >= limit) {
+        // todo take offset into account
+        std::stringstream msg;
+        msg << "program instruction limit of " << limit << " instruction(s) exceeded";
+        throw syntax_error(inst->location, msg.str());
+    }
+    if (!sideset_opt && !inst->sideset) {
+        std::stringstream msg;
+        msg << "instruction requires 'side' to specify side set value for the instruction because non optional sideset was specified for the program at " << sideset.location;
+        throw syntax_error(inst->location, msg.str());
+    }
+    instructions.push_back(inst);
+}
+
+using syntax_error = yy::parser::syntax_error;
+
+void program::add_symbol(std::shared_ptr<symbol> symbol) {
+    const auto &existing = pioasm->get_symbol(symbol->name, this);
+    if (existing) {
+        std::stringstream msg;
+        if (symbol->is_label != existing->is_label) {
+            msg << "'" << symbol->name << "' was already defined as a " << (existing->is_label ? "label" : "value")
+                << " at " << existing->location;
+        } else if (symbol->is_label) {
+            msg << "label '" << symbol->name << "' was already defined at " << existing->location;
+        } else {
+            msg << "'" << symbol->name << "' was already defined at " << existing->location;
+        }
+        throw syntax_error(symbol->location, msg.str());
+    }
+    symbols.insert(std::pair<std::string, std::shared_ptr<::symbol>>(symbol->name, symbol));
+    ordered_symbols.push_back(symbol);
+}
+
+int resolvable::resolve(const program &program) {
+    return resolve(program.pioasm, &program);
+}
+
+int unary_operation::resolve(pio_assembler *pioasm, const program *program, const resolvable &scope) {
+    int value = arg->resolve(pioasm, program, scope);
+    switch (op) {
+        case negate:
+            return -value;
+        case reverse: {
+            // slow is fine
+            uint result = 0;
+            for (uint i = 0; i < 32; i++) {
+                result <<= 1u;
+                if (value & 1u) {
+                    result |= 1u;
+                }
+                value >>= 1u;
+            }
+            return result;
+        }
+        default:
+            throw syntax_error(location, "internal error");
+    }
+}
+
+int binary_operation::resolve(pio_assembler *pioasm, const program *program, const resolvable &scope) {
+    int lvalue = left->resolve(pioasm, program, scope);
+    int rvalue = right->resolve(pioasm, program, scope);
+    switch (op) {
+        case add:
+            return lvalue + rvalue;
+        case subtract:
+            return lvalue - rvalue;
+        case multiply:
+            return lvalue * rvalue;
+        case divide:
+            return lvalue / rvalue;
+        case and_:
+            return lvalue & rvalue;
+        case or_:
+            return lvalue | rvalue;
+        case xor_:
+            return lvalue ^ rvalue;
+        default:
+            throw syntax_error(location, "internal error");
+    }
+}
+
+void program::set_wrap(const yy::location &l) {
+    if (wrap) {
+        std::stringstream msg;
+        msg << ".wrap was already specified at " << wrap->location;
+        throw syntax_error(l, msg.str());
+    }
+    if (instructions.empty()) {
+        throw syntax_error(l, ".wrap cannot be placed before the first program instruction");
+    }
+    wrap = resolvable_int(l, instructions.size() - 1);
+}
+
+void program::set_wrap_target(const yy::location &l) {
+    if (wrap_target) {
+        std::stringstream msg;
+        msg << ".wrap_target was already specified at " << wrap_target->location;
+        throw syntax_error(l, msg.str());
+    }
+    wrap_target = resolvable_int(l, instructions.size());
+}
+
+void program::add_code_block(const code_block &block) {
+    code_blocks[block.lang].push_back(block);
+}
+
+void program::add_lang_opt(std::string lang, std::string name, std::string value) {
+    lang_opts[lang].emplace_back(name, value);
+}
+
+void program::finalize() {
+    if (sideset.value) {
+        int bits = sideset.value->resolve(*this);
+        if (bits < 0) {
+            throw syntax_error(sideset.value->location, "number of side set bits must be positive");
+        }
+        sideset_max = (1u << bits) - 1;
+        if (sideset_opt) bits++;
+        sideset_bits_including_opt = bits;
+        if (bits > 5) {
+            if (sideset_opt)
+                throw syntax_error(sideset.value->location, "maximum number of side set bits with optional is 4");
+            else
+                throw syntax_error(sideset.value->location, "maximum number of side set bits is 5");
+        }
+        delay_max = (1u << (5 - bits)) - 1;
+    } else {
+        sideset_max = 0;
+        delay_max = 31;
+    }
+}
+
+int name_ref::resolve(pio_assembler *pioasm, const program *program, const resolvable &scope) {
+    auto symbol = pioasm->get_symbol(name, program);
+    if (symbol) {
+        if (symbol->resolve_started) {
+            std::stringstream msg;
+            msg << "circular dependency in definition of '" << name << "'; detected at " << location << ")";
+            throw syntax_error(scope.location, msg.str());
+        }
+        try {
+            symbol->resolve_started++;
+            int rc = symbol->value->resolve(pioasm, program, scope);
+            symbol->resolve_started--;
+            return rc;
+        } catch (syntax_error &e) {
+            symbol->resolve_started--;
+            throw e;
+        }
+    } else {
+        std::stringstream msg;
+        msg << "undefined symbol '" << name << "'";
+        throw syntax_error(location, msg.str());
+    }
+}
+
+uint instruction::encode(const program &program) {
+    raw_encoding raw = raw_encode(program);
+    int _delay = delay->resolve(program);
+    if (_delay < 0) {
+        throw syntax_error(delay->location, "instruction delay must be positive");
+    }
+    if (_delay > program.delay_max) {
+        if (program.delay_max == 31) {
+            throw syntax_error(delay->location, "instruction delay must be <= 31");
+        } else {
+            std::stringstream msg;
+            msg << "the instruction delay limit is " << program.delay_max << " because of the side set specified at "
+                << program.sideset.location;
+            throw syntax_error(delay->location, msg.str());
+        }
+    }
+    int _sideset = 0;
+    if (sideset) {
+        _sideset = sideset->resolve(program);
+        if (_sideset < 0) {
+            throw syntax_error(sideset->location, "side set value must be >=0");
+        }
+        if (_sideset > program.sideset_max) {
+            std::stringstream msg;
+            msg << "the maximum side set value is " << program.sideset_max << " based on the configuration specified at "
+                << program.sideset.location;
+            throw syntax_error(sideset->location, msg.str());
+        }
+        _sideset <<= (5u - program.sideset_bits_including_opt);
+        if (program.sideset_opt) {
+            _sideset |= 0x10u;
+        }
+    }
+    return (((uint) raw.type) << 13u) | (((uint) _delay | (uint) _sideset) << 8u) | (raw.arg1 << 5u) | raw.arg2;
+}
+
+raw_encoding instruction::raw_encode(const program &program) {
+    throw syntax_error(location, "internal error");
+}
+
+uint instr_word::encode(const program &program) {
+    uint value = encoding->resolve(program);
+    if (value > 0xffffu) {
+        throw syntax_error(location, ".word value must be a positive 16 bit value");
+    }
+    return value;
+}
+
+raw_encoding instr_jmp::raw_encode(const program &program) {
+    int dest = target->resolve(program);
+    if (dest < 0) {
+        throw syntax_error(target->location, "jmp target address must be positive");
+    } else if (dest >= (int)program.instructions.size()) {
+        std::stringstream msg;
+        msg << "jmp target address " << dest << " is beyond the end of the program";
+        throw syntax_error(target->location, msg.str());
+    }
+    return {inst_type::jmp, (uint) cond, (uint) dest};
+}
+
+raw_encoding instr_in::raw_encode(const program &program) {
+    int v = value->resolve(program);
+    if (v < 1 || v > 32) {
+        throw syntax_error(value->location, "'in' bit count must be >= 1 and <= 32");
+    }
+    return {inst_type::in, (uint) src, (uint) v & 0x1fu};
+}
+
+raw_encoding instr_out::raw_encode(const program &program) {
+    int v = value->resolve(program);
+    if (v < 1 || v > 32) {
+        throw syntax_error(value->location, "'out' bit count must be >= 1 and <= 32");
+    }
+    return {inst_type::out, (uint) dest, (uint) v & 0x1fu};
+}
+
+raw_encoding instr_set::raw_encode(const program &program) {
+    int v = value->resolve(program);
+    if (v < 0 || v > 31) {
+        throw syntax_error(value->location, "'set' bit count must be >= 0 and <= 31");
+    }
+    return {inst_type::set, (uint) dest, (uint) v};
+}
+
+raw_encoding instr_wait::raw_encode(const program &program) {
+    uint pol = polarity->resolve(program);
+    if (pol > 1) {
+        throw syntax_error(polarity->location, "'wait' polarity must be 0 or 1");
+    }
+    uint arg2 = source->param->resolve(program);
+    switch (source->target) {
+        case wait_source::irq:
+            if (arg2 > 7) throw syntax_error(source->param->location, "irq number must be must be >= 0 and <= 7");
+            break;
+        case wait_source::gpio:
+            if (arg2 > 31)
+                throw syntax_error(source->param->location, "absolute GPIO number must be must be >= 0 and <= 31");
+            break;
+        case wait_source::pin:
+            if (arg2 > 31) throw syntax_error(polarity->location, "pin number must be must be >= 0 and <= 31");
+            break;
+    }
+    return {inst_type::wait, (pol << 2u) | (uint) source->target, arg2 | (source->flag ? 0x10u : 0u)};
+}
+
+raw_encoding instr_irq::raw_encode(const program &program) {
+    uint arg2 = num->resolve(program);
+    if (arg2 > 7) throw syntax_error(num->location, "irq number must be must be >= 0 and <= 7");
+    if (relative) arg2 |= 0x10u;
+    return {inst_type::irq, (uint)modifiers, arg2};
+}
+
+std::vector<compiled_source::symbol> pio_assembler::public_symbols(program &program) {
+    std::vector<std::shared_ptr<symbol>> public_symbols;
+    std::remove_copy_if(program.ordered_symbols.begin(), program.ordered_symbols.end(),
+                        std::inserter(public_symbols, public_symbols.end()),
+                        [](const std::shared_ptr<symbol> &s) { return !s->is_public; });
+
+    std::vector<compiled_source::symbol> rc;
+    std::transform(public_symbols.begin(), public_symbols.end(), std::back_inserter(rc),
+                   [&](const std::shared_ptr<symbol> &s) {
+                       return compiled_source::symbol(s->name, s->value->resolve(program), s->is_label);
+                   });
+    return rc;
+}
+
+int pio_assembler::write_output() {
+    std::set<std::string> known_output_formats;
+    std::transform(output_format::all().begin(), output_format::all().end(),
+                   std::inserter(known_output_formats, known_output_formats.begin()),
+                   [&](std::shared_ptr<output_format> &f) {
+                       return f->name;
+                   });
+
+    compiled_source source;
+    source.global_symbols = public_symbols(get_dummy_global_program());
+    for (auto &program : programs) {
+        program.finalize();
+        source.programs.emplace_back(compiled_source::program(program.name));
+        auto &cprogram = source.programs[source.programs.size() - 1];
+        cprogram = compiled_source::program(program.name);
+
+        // encode the instructions
+        std::transform(program.instructions.begin(), program.instructions.end(),
+                       std::back_inserter(cprogram.instructions), [&](std::shared_ptr<instruction> &inst) {
+                    return inst->encode(program);
+                });
+
+        for (const auto &e : program.code_blocks) {
+            bool ok = false;
+            for(const auto &o : known_output_formats) {
+                if (o == e.first || 0 == e.first.find(o+"-")) {
+                    ok = true;
+                    break;
+                }
+            }
+            if (!ok) {
+                std::cerr << e.second[0].location << ": warning, unknown code block output type '" << e.first << "'\n";
+                known_output_formats.insert(e.first);
+            }
+        }
+
+        if (program.wrap) cprogram.wrap = program.wrap->resolve(program); else cprogram.wrap = std::max((int)program.instructions.size() - 1, 0);
+        if (program.wrap_target) cprogram.wrap_target = program.wrap_target->resolve(program); else cprogram.wrap_target = 0;
+        if (program.origin.value) cprogram.origin = program.origin.value->resolve(program);
+        if (program.sideset.value) {
+            cprogram.sideset_bits_including_opt = program.sideset_bits_including_opt;
+            cprogram.sideset_opt = program.sideset_opt;
+            cprogram.sideset_pindirs = program.sideset_pindirs;
+        }
+        std::transform(program.code_blocks.begin(), program.code_blocks.end(), std::inserter(cprogram.code_blocks, cprogram.code_blocks.begin()), [](const std::pair<std::string, std::vector<code_block>>&e) {
+            std::vector<std::string> blocks;
+            std::transform(e.second.begin(), e.second.end(), std::back_inserter(blocks), [&](const code_block& block) {
+                return block.contents;
+            });
+            return std::pair<std::string, std::vector<std::string>>(e.first, blocks);
+        });
+        cprogram.lang_opts = program.lang_opts;
+        cprogram.symbols = public_symbols(program);
+    }
+    if (programs.empty()) {
+        std::cout << "warning: input contained no programs" << std::endl;
+    }
+    return format->output(dest, options, source);
+}
+
+FILE *output_format::open_single_output(std::string destination) {
+    FILE *out = destination == "-" ? stdout : fopen(destination.c_str(), "w");
+    if (!out) {
+        std::cerr << "Can't open output file '" << destination << "'" << std::endl;
+    }
+    return out;
+}