corrects tohost functionality and minor cleanup

src/iss/arch/riscv_hart_common.h

@@ -36,11 +36,14 @@
 #define _RISCV_HART_COMMON
 
 #include "iss/vm_types.h"
+#include <array>
 #include <cstdint>
 #include <elfio/elfio.hpp>
 #include <fmt/format.h>
 #include <iss/arch_if.h>
 #include <iss/log_categories.h>
+#include <limits>
+#include <sstream>
 #include <string>
 #include <unordered_map>
 #include <util/logging.h>
@@ -56,8 +59,6 @@
 namespace iss {
 namespace arch {
 
-enum { tohost_dflt = 0xF0001000, fromhost_dflt = 0xF0001040 };
-
 enum features_e { FEAT_NONE, FEAT_PMP = 1, FEAT_EXT_N = 2, FEAT_CLIC = 4, FEAT_DEBUG = 8, FEAT_TCM = 16 };
 
 enum riscv_csr {
@@ -316,8 +317,8 @@ struct riscv_hart_common {
     ~riscv_hart_common(){};
     std::unordered_map<std::string, uint64_t> symbol_table;
     uint64_t entry_address{0};
-    uint64_t tohost = tohost_dflt;
+    uint64_t tohost = std::numeric_limits<uint64_t>::max();
-    uint64_t fromhost = fromhost_dflt;
+    uint64_t fromhost = std::numeric_limits<uint64_t>::max();
 
     bool read_elf_file(std::string name, uint8_t expected_elf_class,
                        std::function<iss::status(uint64_t, uint64_t, const uint8_t* const)> cb) {
@@ -365,11 +366,10 @@ struct riscv_hart_common {
                 }
                 try {
                     tohost = symbol_table.at("tohost");
+                } catch(std::out_of_range& e) {
+                }
                 try {
                     fromhost = symbol_table.at("fromhost");
-                    } catch(std::out_of_range& e) {
-                        fromhost = tohost + 0x40;
-                    }
                 } catch(std::out_of_range& e) {
                 }
             }
@@ -377,6 +377,36 @@ struct riscv_hart_common {
         }
         return false;
     };
+    iss::status execute_sys_write(arch_if* aif, const std::array<uint64_t, 8>& loaded_payload, unsigned mem_type) {
+        std::stringstream io_buf;
+        uint64_t fd = loaded_payload[1];
+        uint64_t buf_ptr = loaded_payload[2];
+        uint64_t len = loaded_payload[3];
+        std::vector<char> buf(len);
+        if(aif->read(address_type::PHYSICAL, access_type::DEBUG_READ, mem_type, buf_ptr, len, reinterpret_cast<uint8_t*>(buf.data()))) {
+            CPPLOG(ERR) << "SYS_WRITE buffer read went wrong";
+            return iss::Err;
+        }
+        // we disregard the fd and just log to stdout
+        for(size_t i = 0; i < len; i++) {
+            if(buf[i] == '\n') {
+                CPPLOG(INFO) << "tohost send '" << io_buf.str() << "'";
+                io_buf.str("");
+            } else
+                io_buf << buf[i];
+        }
+        if(io_buf.str().length()) {
+            CPPLOG(INFO) << "tohost send '" << io_buf.str() << "'";
+        }
+        // Not sure what the correct return value should be
+        uint8_t ret_val = 1;
+        if(fromhost != std::numeric_limits<uint64_t>::max())
+            if(aif->write(address_type::PHYSICAL, access_type::DEBUG_WRITE, mem_type, fromhost, 1, &ret_val)) {
+                CPPLOG(ERR) << "Fromhost write went wrong";
+                return iss::Err;
+            }
+        return iss::Ok;
+    }
 };
 
 } // namespace arch

src/iss/arch/riscv_hart_m_p.h

@@ -41,7 +41,11 @@
 #include "iss/vm_if.h"
 #include "iss/vm_types.h"
 #include "riscv_hart_common.h"
+#include "util/logging.h"
+#include <algorithm>
+#include <cstdint>
 #include <elfio/elf_types.hpp>
+#include <limits>
 #include <stdexcept>
 #ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
@@ -344,7 +348,6 @@ protected:
     int64_t instret_offset{0};
     uint64_t minstret_csr{0};
     reg_t fault_data;
-    bool tohost_lower_written = false;
     riscv_instrumentation_if instr_if;
 
     semihosting_cb_t<reg_t> semihosting_cb;
@@ -354,7 +357,6 @@ protected:
     using csr_page_type = typename csr_type::page_type;
     mem_type mem;
     csr_type csr;
-    std::stringstream uart_buf;
     std::unordered_map<reg_t, uint64_t> ptw;
     std::unordered_map<uint64_t, uint8_t> atomic_reservation;
     std::unordered_map<unsigned, rd_csr_f> csr_rd_cb;
@@ -446,7 +448,6 @@ riscv_hart_m_p<BASE, FEAT, LOGCAT>::riscv_hart_m_p(feature_config cfg)
     csr[marchid] = traits<BASE>::MARCHID_VAL;
     csr[mimpid] = 1;
 
-    uart_buf.str("");
     if(traits<BASE>::FLEN > 0) {
         csr_rd_cb[fcsr] = &this_class::read_fcsr;
         csr_wr_cb[fcsr] = &this_class::write_fcsr;
@@ -610,7 +611,7 @@ iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::read(const address_type type, co
     try {
         switch(space) {
         case traits<BASE>::MEM: {
-            auto alignment = is_fetch(access) ? (has_compressed() ? 2 : 4) : length;
+            auto alignment = is_fetch(access) ? (has_compressed() ? 2 : 4) : std::min<unsigned>(length, sizeof(reg_t));
             if(unlikely(is_fetch(access) && (addr & (alignment - 1)))) {
                 fault_data = addr;
                 if(is_debug(access))
@@ -720,7 +721,8 @@ iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::write(const address_type type, c
                 return iss::Err;
             }
             try {
-                if(length > 1 && (addr & (length - 1)) && (access & access_type::DEBUG) != access_type::DEBUG) {
+                auto alignment = std::min<unsigned>(length, sizeof(reg_t));
+                if(length > 1 && (addr & (alignment - 1)) && !is_debug(access)) {
                     this->reg.trap_state = (1UL << 31) | 6 << 16;
                     fault_data = addr;
                     return iss::Err;
@@ -740,7 +742,7 @@ iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::write(const address_type type, c
                 } else {
                     res = write_mem(phys_addr, length, data);
                 }
-                if(unlikely(res != iss::Ok && (access & access_type::DEBUG) == 0)) {
+                if(unlikely(res != iss::Ok && !is_debug(access))) {
                     this->reg.trap_state = (1UL << 31) | (7UL << 16); // issue trap 7 (Store/AMO access fault)
                     fault_data = addr;
                 }
@@ -750,38 +752,6 @@ iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::write(const address_type type, c
                 fault_data = ta.addr;
                 return iss::Err;
             }
-
-            if((addr + length) > mem.size())
-                return iss::Err;
-            switch(addr) {
-            case 0x10013000: // UART0 base, TXFIFO reg
-            case 0x10023000: // UART1 base, TXFIFO reg
-                uart_buf << (char)data[0];
-                if(((char)data[0]) == '\n' || data[0] == 0) {
-                    std::cout << uart_buf.str();
-                    uart_buf.str("");
-                }
-                return iss::Ok;
-            case 0x10008000: { // HFROSC base, hfrosccfg reg
-                auto& p = mem(addr / mem.page_size);
-                auto offs = addr & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                if(x & 0x40)
-                    x |= 0x80; // hfroscrdy = 1 if hfroscen==1
-                return iss::Ok;
-            }
-            case 0x10008008: { // HFROSC base, pllcfg reg
-                auto& p = mem(addr / mem.page_size);
-                auto offs = addr & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                x |= 0x80; // set pll lock upon writing
-                return iss::Ok;
-            } break;
-            default: {
-            }
-            }
         } break;
         case traits<BASE>::CSR: {
             if(length != sizeof(reg_t))
@@ -1094,60 +1064,52 @@ iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::read_mem(phys_addr_t paddr, unsi
 
 template <typename BASE, features_e FEAT, typename LOGCAT>
 iss::status riscv_hart_m_p<BASE, FEAT, LOGCAT>::write_mem(phys_addr_t paddr, unsigned length, const uint8_t* const data) {
-    switch(paddr.val) {
-    // TODO remove UART, Peripherals should not be part of the ISS
-    case 0xFFFF0000: // UART0 base, TXFIFO reg
-        if(((char)data[0]) == '\n' || data[0] == 0) {
-            CPPLOG(INFO) << "UART" << ((paddr.val >> 12) & 0x3) << " send '" << uart_buf.str() << "'";
-            uart_buf.str("");
-        } else if(((char)data[0]) != '\r')
-            uart_buf << (char)data[0];
-        break;
-    default: {
     mem_type::page_type& p = mem(paddr.val / mem.page_size);
     std::copy(data, data + length, p.data() + (paddr.val & mem.page_addr_mask));
     // tohost handling in case of riscv-test
+    // according to https://github.com/riscv-software-src/riscv-isa-sim/issues/364#issuecomment-607657754:
     if(paddr.access && iss::access_type::FUNC) {
-            auto tohost_upper =
+        if(paddr.val == tohost) {
-                (traits<BASE>::XLEN == 32 && paddr.val == (tohost + 4)) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            reg_t cur_data = *reinterpret_cast<const reg_t*>(data);
-            auto tohost_lower = (traits<BASE>::XLEN == 32 && paddr.val == tohost) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            // Extract Device (bits 63:56)
-            if(tohost_lower || tohost_upper) {
+            uint8_t device = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 56) & 0xFF;
-                uint64_t hostvar = *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask));
+            // Extract Command (bits 55:48)
-                // in case of 32 bit system, two writes to tohost are needed, only evaluate on the second (high) write
+            uint8_t command = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 48) & 0xFF;
-                if(tohost_upper && (tohost_lower || tohost_lower_written)) {
+            // Extract payload (bits 47:0)
-                    switch(hostvar >> 48) {
+            uint64_t payload_addr = cur_data & 0xFFFFFFFFFFFFULL;
-                    case 0:
+            if(payload_addr & 1) {
-                        if(hostvar != 0x1) {
+                CPPLOG(FATAL) << "tohost value is 0x" << std::hex << payload_addr << std::dec << " (" << payload_addr
-                            CPPLOG(FATAL) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
                               << "), stopping simulation";
-                        } else {
-                            CPPLOG(INFO) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
-                                         << "), stopping simulation";
-                        }
                 this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-                        this->interrupt_sim = hostvar;
+                this->interrupt_sim = payload_addr;
-                        break;
+                return iss::Ok;
-                    case 0x0101: {
+            } else if(device == 0 && command == 0) {
-                        char c = static_cast<char>(hostvar & 0xff);
+                std::array<uint64_t, 8> loaded_payload;
-                        if(c == '\n' || c == 0) {
+                if(read(address_type::PHYSICAL, access_type::DEBUG_READ, traits<BASE>::MEM, payload_addr, 8 * sizeof(uint64_t),
-                            CPPLOG(INFO) << "tohost send '" << uart_buf.str() << "'";
+                        reinterpret_cast<uint8_t*>(loaded_payload.data())) == iss::Err)
-                            uart_buf.str("");
+                    CPPLOG(ERR) << "Syscall read went wrong";
-                        } else
+                uint64_t syscall_num = loaded_payload.at(0);
-                            uart_buf << c;
+                if(syscall_num == 64) { // SYS_WRITE
-                    } break;
+                    return execute_sys_write(this, loaded_payload, traits<BASE>::MEM);
-                    default:
+                } else {
-                        break;
+                    CPPLOG(ERR) << "tohost syscall with number 0x" << std::hex << syscall_num << std::dec << " (" << syscall_num
+                                << ") not implemented";
+                    this->reg.trap_state = std::numeric_limits<uint32_t>::max();
+                    this->interrupt_sim = payload_addr;
+                    return iss::Ok;
                 }
-                    tohost_lower_written = false;
+            } else {
-                } else if(tohost_lower)
+                CPPLOG(ERR) << "tohost functionality not implemented for device " << device << " and command " << command;
-                    tohost_lower_written = true;
+                this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-            } else if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
+                this->interrupt_sim = payload_addr;
+                return iss::Ok;
+            }
+        }
+        if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
             uint64_t fhostvar = *reinterpret_cast<uint64_t*>(p.data() + (fromhost & mem.page_addr_mask));
             *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask)) = fhostvar;
         }
     }
-    }
-    }
     return iss::Ok;
 }
 

src/iss/arch/riscv_hart_msu_vp.h

@@ -41,6 +41,11 @@
 #include "iss/vm_if.h"
 #include "iss/vm_types.h"
 #include "riscv_hart_common.h"
+#include "util/logging.h"
+#include <algorithm>
+#include <cstdint>
+#include <elfio/elf_types.hpp>
+#include <limits>
 #include <stdexcept>
 #ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
@@ -393,7 +398,6 @@ protected:
     uint64_t minstret_csr{0};
     reg_t fault_data;
     std::array<vm_info, 2> vm;
-    bool tohost_lower_written = false;
     riscv_instrumentation_if instr_if;
 
     std::function<void(arch_if*, reg_t, reg_t)> semihosting_cb;
@@ -404,7 +408,6 @@ protected:
     mem_type mem;
     csr_type csr;
     void update_vm_info();
-    std::stringstream uart_buf;
     std::unordered_map<reg_t, uint64_t> ptw;
     std::unordered_map<uint64_t, uint8_t> atomic_reservation;
     std::unordered_map<unsigned, rd_csr_f> csr_rd_cb;
@@ -459,7 +462,6 @@ riscv_hart_msu_vp<BASE>::riscv_hart_msu_vp()
     csr[marchid] = traits<BASE>::MARCHID_VAL;
     csr[mimpid] = 1;
 
-    uart_buf.str("");
     for(unsigned addr = mhpmcounter3; addr <= mhpmcounter31; ++addr) {
         csr_rd_cb[addr] = &this_class::read_null;
         csr_wr_cb[addr] = &this_class::write_csr_reg;
@@ -580,7 +582,7 @@ iss::status riscv_hart_msu_vp<BASE>::read(const address_type type, const access_
     try {
         switch(space) {
         case traits<BASE>::MEM: {
-            auto alignment = is_fetch(access) ? (traits<BASE>::MISA_VAL & 0x100 ? 2 : 4) : length;
+            auto alignment = is_fetch(access) ? (has_compressed() ? 2 : 4) : std::min<unsigned>(length, sizeof(reg_t));
             if(unlikely(is_fetch(access) && (addr & (alignment - 1)))) {
                 fault_data = addr;
                 if(access && iss::access_type::DEBUG)
@@ -699,6 +701,7 @@ iss::status riscv_hart_msu_vp<BASE>::write(const address_type type, const access
             }
             phys_addr_t paddr = BASE::v2p(iss::addr_t{access, type, space, addr});
             try {
+                // TODO: There is no check for alignment
                 if(unlikely((addr & ~PGMASK) != ((addr + length - 1) & ~PGMASK))) { // we may cross a page boundary
                     vm_info vm = hart_state_type::decode_vm_info(this->reg.PRIV, state.satp);
                     if(vm.levels != 0) { // VM is active
@@ -721,40 +724,6 @@ iss::status riscv_hart_msu_vp<BASE>::write(const address_type type, const access
                 fault_data = ta.addr;
                 return iss::Err;
             }
-
-            if((paddr.val + length) > mem.size())
-                return iss::Err;
-            switch(paddr.val) {
-            case 0x10013000: // UART0 base, TXFIFO reg
-            case 0x10023000: // UART1 base, TXFIFO reg
-                uart_buf << (char)data[0];
-                if(((char)data[0]) == '\n' || data[0] == 0) {
-                    // CPPLOG(INFO)<<"UART"<<((paddr.val>>16)&0x3)<<" send
-                    // '"<<uart_buf.str()<<"'";
-                    std::cout << uart_buf.str();
-                    uart_buf.str("");
-                }
-                return iss::Ok;
-            case 0x10008000: { // HFROSC base, hfrosccfg reg
-                auto& p = mem(paddr.val / mem.page_size);
-                auto offs = paddr.val & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                if(x & 0x40)
-                    x |= 0x80; // hfroscrdy = 1 if hfroscen==1
-                return iss::Ok;
-            }
-            case 0x10008008: { // HFROSC base, pllcfg reg
-                auto& p = mem(paddr.val / mem.page_size);
-                auto offs = paddr.val & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                x |= 0x80; // set pll lock upon writing
-                return iss::Ok;
-            } break;
-            default: {
-            }
-            }
         } break;
         case traits<BASE>::CSR: {
             if(length != sizeof(reg_t))
@@ -1024,62 +993,52 @@ template <typename BASE> iss::status riscv_hart_msu_vp<BASE>::read_mem(phys_addr
 }
 
 template <typename BASE> iss::status riscv_hart_msu_vp<BASE>::write_mem(phys_addr_t paddr, unsigned length, const uint8_t* const data) {
-    switch(paddr.val) {
-    case 0xFFFF0000: // UART0 base, TXFIFO reg
-        if(((char)data[0]) == '\n' || data[0] == 0) {
-            CPPLOG(INFO) << "UART" << ((paddr.val >> 12) & 0x3) << " send '" << uart_buf.str() << "'";
-            uart_buf.str("");
-        } else if(((char)data[0]) != '\r')
-            uart_buf << (char)data[0];
-        break;
-    default: {
     mem_type::page_type& p = mem(paddr.val / mem.page_size);
     std::copy(data, data + length, p.data() + (paddr.val & mem.page_addr_mask));
     // tohost handling in case of riscv-test
+    // according to https://github.com/riscv-software-src/riscv-isa-sim/issues/364#issuecomment-607657754:
     if(paddr.access && iss::access_type::FUNC) {
-            auto tohost_upper =
+        if(paddr.val == tohost) {
-                (traits<BASE>::XLEN == 32 && paddr.val == (tohost + 4)) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            reg_t cur_data = *reinterpret_cast<const reg_t*>(data);
-            auto tohost_lower = (traits<BASE>::XLEN == 32 && paddr.val == tohost) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            // Extract Device (bits 63:56)
-            if(tohost_lower || tohost_upper) {
+            uint8_t device = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 56) & 0xFF;
-                uint64_t hostvar = *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask));
+            // Extract Command (bits 55:48)
-                // in case of 32 bit system, two writes to tohost are needed, only evaluate on the second (high) write
+            uint8_t command = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 48) & 0xFF;
-                if(tohost_upper && (tohost_lower || tohost_lower_written)) {
+            // Extract payload (bits 47:0)
-                    switch(hostvar >> 48) {
+            uint64_t payload_addr = cur_data & 0xFFFFFFFFFFFFULL;
-                    case 0:
+            if(payload_addr & 1) {
-                        if(hostvar != 0x1) {
+                CPPLOG(FATAL) << "tohost value is 0x" << std::hex << payload_addr << std::dec << " (" << payload_addr
-                            CPPLOG(FATAL) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
                               << "), stopping simulation";
-                        } else {
-                            CPPLOG(INFO) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
-                                         << "), stopping simulation";
-                        }
                 this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-                        this->interrupt_sim = hostvar;
+                this->interrupt_sim = payload_addr;
-#ifndef WITH_TCC
+                return iss::Ok;
-                        throw(iss::simulation_stopped(hostvar));
+            } else if(device == 0 && command == 0) {
-#endif
+                std::array<uint64_t, 8> loaded_payload;
-                        break;
+                if(read(address_type::PHYSICAL, access_type::DEBUG_READ, traits<BASE>::MEM, payload_addr, 8 * sizeof(uint64_t),
-                    case 0x0101: {
+                        reinterpret_cast<uint8_t*>(loaded_payload.data())) == iss::Err)
-                        char c = static_cast<char>(hostvar & 0xff);
+                    CPPLOG(ERR) << "Syscall read went wrong";
-                        if(c == '\n' || c == 0) {
+                uint64_t syscall_num = loaded_payload.at(0);
-                            CPPLOG(INFO) << "tohost send '" << uart_buf.str() << "'";
+                if(syscall_num == 64) { // SYS_WRITE
-                            uart_buf.str("");
+                    return execute_sys_write(this, loaded_payload, traits<BASE>::MEM);
-                        } else
+                } else {
-                            uart_buf << c;
+                    CPPLOG(ERR) << "tohost syscall with number 0x" << std::hex << syscall_num << std::dec << " (" << syscall_num
-                    } break;
+                                << ") not implemented";
-                    default:
+                    this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-                        break;
+                    this->interrupt_sim = payload_addr;
+                    return iss::Ok;
                 }
-                    tohost_lower_written = false;
+            } else {
-                } else if(tohost_lower)
+                CPPLOG(ERR) << "tohost functionality not implemented for device " << device << " and command " << command;
-                    tohost_lower_written = true;
+                this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-            } else if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
+                this->interrupt_sim = payload_addr;
+                return iss::Ok;
+            }
+        }
+        if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
             uint64_t fhostvar = *reinterpret_cast<uint64_t*>(p.data() + (fromhost & mem.page_addr_mask));
             *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask)) = fhostvar;
         }
     }
-    }
-    }
     return iss::Ok;
 }
 

src/iss/arch/riscv_hart_mu_p.h

@@ -41,6 +41,11 @@
 #include "iss/vm_if.h"
 #include "iss/vm_types.h"
 #include "riscv_hart_common.h"
+#include "util/logging.h"
+#include <algorithm>
+#include <cstdint>
+#include <elfio/elf_types.hpp>
+#include <limits>
 #include <stdexcept>
 #ifndef FMT_HEADER_ONLY
 #define FMT_HEADER_ONLY
@@ -370,7 +375,6 @@ protected:
     int64_t instret_offset{0};
     uint64_t minstret_csr{0};
     reg_t fault_data;
-    bool tohost_lower_written = false;
     riscv_instrumentation_if instr_if;
 
     semihosting_cb_t<reg_t> semihosting_cb;
@@ -380,7 +384,6 @@ protected:
     using csr_page_type = typename csr_type::page_type;
     mem_type mem;
     csr_type csr;
-    std::stringstream uart_buf;
     std::unordered_map<reg_t, uint64_t> ptw;
     std::unordered_map<uint64_t, uint8_t> atomic_reservation;
     std::unordered_map<unsigned, rd_csr_f> csr_rd_cb;
@@ -475,7 +478,6 @@ riscv_hart_mu_p<BASE, FEAT, LOGCAT>::riscv_hart_mu_p(feature_config cfg)
     csr[marchid] = traits<BASE>::MARCHID_VAL;
     csr[mimpid] = 1;
 
-    uart_buf.str("");
     if(traits<BASE>::FLEN > 0) {
         csr_rd_cb[fcsr] = &this_class::read_fcsr;
         csr_wr_cb[fcsr] = &this_class::write_fcsr;
@@ -783,7 +785,7 @@ iss::status riscv_hart_mu_p<BASE, FEAT, LOGCAT>::read(const address_type type, c
                     return iss::Err;
                 }
             }
-            auto alignment = is_fetch(access) ? (has_compressed() ? 2 : 4) : length;
+            auto alignment = is_fetch(access) ? (has_compressed() ? 2 : 4) : std::min<unsigned>(length, sizeof(reg_t));
             if(unlikely(is_fetch(access) && (addr & (alignment - 1)))) {
                 fault_data = addr;
                 if(is_debug(access))
@@ -902,7 +904,8 @@ iss::status riscv_hart_mu_p<BASE, FEAT, LOGCAT>::write(const address_type type,
                 return iss::Err;
             }
             try {
-                if(length > 1 && (addr & (length - 1)) && (access & access_type::DEBUG) != access_type::DEBUG) {
+                auto alignment = std::min<unsigned>(length, sizeof(reg_t));
+                if(length > 1 && (addr & (alignment - 1)) && !is_debug(access)) {
                     this->reg.trap_state = (1UL << 31) | 6 << 16;
                     fault_data = addr;
                     return iss::Err;
@@ -932,38 +935,6 @@ iss::status riscv_hart_mu_p<BASE, FEAT, LOGCAT>::write(const address_type type,
                 fault_data = ta.addr;
                 return iss::Err;
             }
-
-            if((addr + length) > mem.size())
-                return iss::Err;
-            switch(addr) {
-            case 0x10013000: // UART0 base, TXFIFO reg
-            case 0x10023000: // UART1 base, TXFIFO reg
-                uart_buf << (char)data[0];
-                if(((char)data[0]) == '\n' || data[0] == 0) {
-                    std::cout << uart_buf.str();
-                    uart_buf.str("");
-                }
-                return iss::Ok;
-            case 0x10008000: { // HFROSC base, hfrosccfg reg
-                auto& p = mem(addr / mem.page_size);
-                auto offs = addr & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                if(x & 0x40)
-                    x |= 0x80; // hfroscrdy = 1 if hfroscen==1
-                return iss::Ok;
-            }
-            case 0x10008008: { // HFROSC base, pllcfg reg
-                auto& p = mem(addr / mem.page_size);
-                auto offs = addr & mem.page_addr_mask;
-                std::copy(data, data + length, p.data() + offs);
-                auto& x = *(p.data() + offs + 3);
-                x |= 0x80; // set pll lock upon writing
-                return iss::Ok;
-            } break;
-            default: {
-            }
-            }
         } break;
         case traits<BASE>::CSR: {
             if(length != sizeof(reg_t))
@@ -1312,66 +1283,54 @@ iss::status riscv_hart_mu_p<BASE, FEAT, LOGCAT>::read_mem(phys_addr_t paddr, uns
     }
     return iss::Ok;
 }
-
 template <typename BASE, features_e FEAT, typename LOGCAT>
 iss::status riscv_hart_mu_p<BASE, FEAT, LOGCAT>::write_mem(phys_addr_t paddr, unsigned length, const uint8_t* const data) {
-    switch(paddr.val) {
-    // TODO remove UART, Peripherals should not be part of the ISS
-    case 0xFFFF0000: // UART0 base, TXFIFO reg
-        if(((char)data[0]) == '\n' || data[0] == 0) {
-            CPPLOG(INFO) << "UART" << ((paddr.val >> 12) & 0x3) << " send '" << uart_buf.str() << "'";
-            uart_buf.str("");
-        } else if(((char)data[0]) != '\r')
-            uart_buf << (char)data[0];
-        break;
-    default: {
     mem_type::page_type& p = mem(paddr.val / mem.page_size);
     std::copy(data, data + length, p.data() + (paddr.val & mem.page_addr_mask));
     // tohost handling in case of riscv-test
+    // according to https://github.com/riscv-software-src/riscv-isa-sim/issues/364#issuecomment-607657754:
     if(paddr.access && iss::access_type::FUNC) {
-            auto tohost_upper =
+        if(paddr.val == tohost) {
-                (traits<BASE>::XLEN == 32 && paddr.val == (tohost + 4)) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            reg_t cur_data = *reinterpret_cast<const reg_t*>(data);
-            auto tohost_lower = (traits<BASE>::XLEN == 32 && paddr.val == tohost) || (traits<BASE>::XLEN == 64 && paddr.val == tohost);
+            // Extract Device (bits 63:56)
-            if(tohost_lower || tohost_upper) {
+            uint8_t device = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 56) & 0xFF;
-                uint64_t hostvar = *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask));
+            // Extract Command (bits 55:48)
-                // in case of 32 bit system, two writes to tohost are needed, only evaluate on the second (high) write
+            uint8_t command = traits<BASE>::XLEN == 32 ? 0 : (cur_data >> 48) & 0xFF;
-                if(tohost_upper && (tohost_lower || tohost_lower_written)) {
+            // Extract payload (bits 47:0)
-                    switch(hostvar >> 48) {
+            uint64_t payload_addr = cur_data & 0xFFFFFFFFFFFFULL;
-                    case 0:
+            if(payload_addr & 1) {
-                        if(hostvar != 0x1) {
+                CPPLOG(FATAL) << "tohost value is 0x" << std::hex << payload_addr << std::dec << " (" << payload_addr
-                            CPPLOG(FATAL) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
                               << "), stopping simulation";
-                        } else {
-                            CPPLOG(INFO) << "tohost value is 0x" << std::hex << hostvar << std::dec << " (" << hostvar
-                                         << "), stopping simulation";
-                        }
                 this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-                        this->interrupt_sim = hostvar;
+                this->interrupt_sim = payload_addr;
-#ifndef WITH_TCC
+                return iss::Ok;
-                        throw(iss::simulation_stopped(hostvar));
+            } else if(device == 0 && command == 0) {
-#endif
+                std::array<uint64_t, 8> loaded_payload;
-                        break;
+                if(read(address_type::PHYSICAL, access_type::DEBUG_READ, traits<BASE>::MEM, payload_addr, 8 * sizeof(uint64_t),
-                    case 0x0101: {
+                        reinterpret_cast<uint8_t*>(loaded_payload.data())) == iss::Err)
-                        char c = static_cast<char>(hostvar & 0xff);
+                    CPPLOG(ERR) << "Syscall read went wrong";
-                        if(c == '\n' || c == 0) {
+                uint64_t syscall_num = loaded_payload.at(0);
-                            CPPLOG(INFO) << "tohost send '" << uart_buf.str() << "'";
+                if(syscall_num == 64) { // SYS_WRITE
-                            uart_buf.str("");
+                    return execute_sys_write(this, loaded_payload, traits<BASE>::MEM);
-                        } else
+                } else {
-                            uart_buf << c;
+                    CPPLOG(ERR) << "tohost syscall with number 0x" << std::hex << syscall_num << std::dec << " (" << syscall_num
-                    } break;
+                                << ") not implemented";
-                    default:
+                    this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-                        break;
+                    this->interrupt_sim = payload_addr;
+                    return iss::Ok;
                 }
-                    tohost_lower_written = false;
+            } else {
-                } else if(tohost_lower)
+                CPPLOG(ERR) << "tohost functionality not implemented for device " << device << " and command " << command;
-                    tohost_lower_written = true;
+                this->reg.trap_state = std::numeric_limits<uint32_t>::max();
-            } else if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
+                this->interrupt_sim = payload_addr;
+                return iss::Ok;
+            }
+        }
+        if((traits<BASE>::XLEN == 32 && paddr.val == fromhost + 4) || (traits<BASE>::XLEN == 64 && paddr.val == fromhost)) {
             uint64_t fhostvar = *reinterpret_cast<uint64_t*>(p.data() + (fromhost & mem.page_addr_mask));
             *reinterpret_cast<uint64_t*>(p.data() + (tohost & mem.page_addr_mask)) = fhostvar;
         }
     }
-    }
-    }
     return iss::Ok;
 }