diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e13e65f..5826c5d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,13 +1,16 @@
-name: nim-chronos CI
-on: [push, pull_request]
+name: CI
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+  workflow_dispatch:
 
 jobs:
   build:
     strategy:
       fail-fast: false
-      max-parallel: 20
       matrix:
-        branch: [master]
         target:
           - os: linux
             cpu: amd64
@@ -17,25 +20,35 @@ jobs:
             cpu: amd64
           - os: windows
             cpu: amd64
-          - os: windows
-            cpu: i386
+          #- os: windows
+            #cpu: i386
+        branch: [version-1-2, version-1-4, version-1-6, devel]
         include:
           - target:
               os: linux
             builder: ubuntu-18.04
+            shell: bash
           - target:
               os: macos
             builder: macos-10.15
+            shell: bash
           - target:
               os: windows
             builder: windows-2019
+            shell: msys2 {0}
 
-    name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (${{ matrix.branch }})'
+    defaults:
+      run:
+        shell: ${{ matrix.shell }}
+
+    name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (Nim ${{ matrix.branch }})'
     runs-on: ${{ matrix.builder }}
+    continue-on-error: ${{ matrix.branch == 'devel' }}
     steps:
       - name: Checkout nim-chronos
         uses: actions/checkout@v2
         with:
+          ref: master
           path: nim-chronos
           submodules: false
 
@@ -59,13 +72,26 @@ jobs:
           chmod 755 external/bin/gcc external/bin/g++
           echo '${{ github.workspace }}/external/bin' >> $GITHUB_PATH
 
-      - name: Restore MinGW-W64 (Windows) from cache
-        if: runner.os == 'Windows'
-        id: windows-mingw-cache
-        uses: actions/cache@v2
+      - name: MSYS2 (Windows i386)
+        if: runner.os == 'Windows' && matrix.target.cpu == 'i386'
+        uses: msys2/setup-msys2@v2
         with:
-          path: external/mingw-${{ matrix.target.cpu }}
-          key: 'mingw-${{ matrix.target.cpu }}'
+          path-type: inherit
+          msystem: MINGW32
+          install: >-
+            base-devel
+            git
+            mingw-w64-i686-toolchain
+
+      - name: MSYS2 (Windows amd64)
+        if: runner.os == 'Windows' && matrix.target.cpu == 'amd64'
+        uses: msys2/setup-msys2@v2
+        with:
+          path-type: inherit
+          install: >-
+            base-devel
+            git
+            mingw-w64-x86_64-toolchain
 
       - name: Restore Nim DLLs dependencies (Windows) from cache
         if: runner.os == 'Windows'
@@ -75,29 +101,10 @@ jobs:
           path: external/dlls-${{ matrix.target.cpu }}
           key: 'dlls-${{ matrix.target.cpu }}'
 
-      - name: Install MinGW64 dependency (Windows)
-        if: >
-          steps.windows-mingw-cache.outputs.cache-hit != 'true' &&
-          runner.os == 'Windows'
-        shell: bash
-        run: |
-          mkdir -p external
-          if [[ '${{ matrix.target.cpu }}' == 'amd64' ]]; then
-            MINGW_URL="https://github.com/brechtsanders/winlibs_mingw/releases/download/11.2.0-12.0.1-9.0.0-r1/winlibs-x86_64-posix-seh-gcc-11.2.0-mingw-w64-9.0.0-r1.7z"
-            ARCH=64
-          else
-            MINGW_URL="https://github.com/brechtsanders/winlibs_mingw/releases/download/11.2.0-12.0.1-9.0.0-r1/winlibs-i686-posix-dwarf-gcc-11.2.0-mingw-w64-9.0.0-r1.7z"
-            ARCH=32
-          fi
-          curl -L "$MINGW_URL" -o "external/mingw-${{ matrix.target.cpu }}.7z"
-          7z x -y "external/mingw-${{ matrix.target.cpu }}.7z" -oexternal/
-          mv external/mingw$ARCH external/mingw-${{ matrix.target.cpu }}
-
       - name: Install DLLs dependencies (Windows)
         if: >
           steps.windows-dlls-cache.outputs.cache-hit != 'true' &&
           runner.os == 'Windows'
-        shell: bash
         run: |
           mkdir -p external
           curl -L "https://nim-lang.org/download/windeps.zip" -o external/windeps.zip
@@ -106,52 +113,49 @@ jobs:
       - name: Path to cached dependencies (Windows)
         if: >
           runner.os == 'Windows'
-        shell: bash
         run: |
-          echo '${{ github.workspace }}'"/external/mingw-${{ matrix.target.cpu }}/bin" >> $GITHUB_PATH
           echo '${{ github.workspace }}'"/external/dlls-${{ matrix.target.cpu }}" >> $GITHUB_PATH
 
-      - name: Get latest nimbus-build-system commit hash
-        id: versions
-        shell: bash
+      - name: Derive environment variables
         run: |
-          getHash() {
-            git ls-remote "https://github.com/$1" "${2:-HEAD}" | cut -f 1
-          }
-          nbsHash=$(getHash status-im/nimbus-build-system)
-          echo "::set-output name=nimbus_build_system::$nbsHash"
-
-      - name: Restore prebuilt Nim from cache
-        id: nim-cache
-        uses: actions/cache@v2
-        with:
-          path: NimBinaries
-          key: 'nim-${{ matrix.target.os }}-${{ matrix.target.cpu }}-${{ steps.versions.outputs.nimbus_build_system }}-2'
-
-      - name: Build Nim and associated tools
-        shell: bash
-        run: |
-          curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus-build-system/master/scripts/build_nim.sh
           if [[ '${{ matrix.target.cpu }}' == 'amd64' ]]; then
             PLATFORM=x64
           else
             PLATFORM=x86
           fi
-          if [[ '${{ matrix.target.os }}' == 'windows' ]]; then
-            MAKE_CMD="mingw32-make"
-          else
-            MAKE_CMD="make"
-          fi
-          env MAKE="$MAKE_CMD -j2" ARCH_OVERRIDE=$PLATFORM CC=gcc bash build_nim.sh nim csources dist/nimble NimBinaries
+          echo "PLATFORM=$PLATFORM" >> $GITHUB_ENV
 
-      - name: Setup environment
-        shell: bash
-        run: echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
+          ncpu=
+          MAKE_CMD="make"
+          case '${{ runner.os }}' in
+          'Linux')
+            ncpu=$(nproc)
+            ;;
+          'macOS')
+            ncpu=$(sysctl -n hw.ncpu)
+            ;;
+          'Windows')
+            ncpu=$NUMBER_OF_PROCESSORS
+            MAKE_CMD="mingw32-make"
+            ;;
+          esac
+          [[ -z "$ncpu" || $ncpu -le 0 ]] && ncpu=1
+          echo "ncpu=$ncpu" >> $GITHUB_ENV
+          echo "MAKE_CMD=${MAKE_CMD}" >> $GITHUB_ENV
+
+      - name: Build Nim and Nimble
+        run: |
+          curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus-build-system/master/scripts/build_nim.sh
+          env MAKE="${MAKE_CMD} -j${ncpu}" ARCH_OVERRIDE=${PLATFORM} NIM_COMMIT=${{ matrix.branch }} \
+            QUICK_AND_DIRTY_COMPILER=1 QUICK_AND_DIRTY_NIMBLE=1 CC=gcc \
+            bash build_nim.sh nim csources dist/nimble NimBinaries
+          echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
 
       - name: Run nim-chronos tests
-        shell: bash
         working-directory: nim-chronos
         run: |
+          nim --version
+          nimble --version
           nimble install -y --depsOnly
           nimble install -y libbacktrace
           nimble test
diff --git a/.github/workflows/multi_nim.yml b/.github/workflows/multi_nim.yml
index 68c4f3d..c7773a7 100644
--- a/.github/workflows/multi_nim.yml
+++ b/.github/workflows/multi_nim.yml
@@ -41,7 +41,7 @@ jobs:
 
     name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (Nim ${{ matrix.branch }})'
     runs-on: ${{ matrix.builder }}
-    continue-on-error: ${{ matrix.branch == 'version-1-6' || matrix.branch == 'devel' }}
+    continue-on-error: ${{ matrix.branch == 'devel' }}
     steps:
       - name: Checkout nim-chronos
         uses: actions/checkout@v2
@@ -152,6 +152,8 @@ jobs:
       - name: Run nim-chronos tests
         working-directory: nim-chronos
         run: |
+          nim --version
+          nimble --version
           nimble install -y --depsOnly
           nimble install -y libbacktrace
           nimble test