sequentially-read-a-file as js module

assets/disk0/tvdos/include/seqread.js

@@ -0,0 +1,137 @@
+
+let readCount = 0
+let port = undefined
+
+function prepare(fullPath) {
+    if (fullPath[2] != '/' && fullPath[2] != '\\') throw Error("Expected full path with drive letter, got " + fullPath)
+
+
+    readCount = 0
+
+    let driveLetter = fullPath[0].toUpperCase()
+    let diskPath = fullPath.substring(2).replaceAll("\\",'/')
+
+    // remove '/' at the head of the diskPath
+    while (diskPath[0] == '/') {
+        diskPath = diskPath.substring(1)
+    }
+
+    port = _TVDOS.DRV.FS.SERIAL._toPorts(driveLetter)[0]
+
+    com.sendMessage(port, "DEVRST\x17")
+    com.sendMessage(port, `OPENR"${diskPath}",1`)
+    let statusCode = com.getStatusCode(port)
+
+    if (statusCode != 0) {
+        throw Error(`No such file (${statusCode}; ${driveLetter}:\\${diskPath})`)
+        return statusCode
+    }
+
+    com.sendMessage(port, "READ")
+    statusCode = com.getStatusCode(port)
+    if (statusCode != 0) {
+        throw Error("READ failed with "+statusCode)
+        return statusCode
+    }
+}
+
+function readBytes(length, ptrToDecode) {
+    if (length <= 0) return
+    let ptr = (ptrToDecode === undefined) ? sys.malloc(length) : ptrToDecode
+    let requiredBlocks = Math.floor((readCount + length) / 4096) - Math.floor(readCount / 4096)
+
+    let completedReads = 0
+
+//    serial.println(`readBytes(${length}); readCount = ${readCount}`)
+
+    for (let bc = 0; bc < requiredBlocks + 1; bc++) {
+        if (completedReads >= length) break
+
+        if (readCount % 4096 == 0) {
+//            serial.println("READ from serial")
+            // pull the actual message
+            sys.poke(-4093 - port, 6);sys.sleep(0) // spinning is required as Graal run is desynced with the Java side
+
+            let blockTransferStatus = ((sys.peek(-4085 - port*2) & 255) | ((sys.peek(-4086 - port*2) & 255) << 8))
+            let thisBlockLen = blockTransferStatus & 4095
+            if (thisBlockLen == 0) thisBlockLen = 4096 // [1, 4096]
+            let hasMore = (blockTransferStatus & 0x8000 != 0)
+
+
+//            serial.println(`block: (${thisBlockLen})[${[...Array(thisBlockLen).keys()].map(k => (sys.peek(-4097 - k) & 255).toString(16).padStart(2,'0')).join()}]`)
+
+            let remaining = Math.min(thisBlockLen, length - completedReads)
+
+//            serial.println(`Pulled a block (${thisBlockLen}); readCount = ${readCount}, completedReads = ${completedReads}, remaining = ${remaining}`)
+
+            // copy from read buffer to designated position
+            sys.memcpy(-4097, ptr + completedReads, remaining)
+
+            // increment readCount properly
+            readCount += remaining
+            completedReads += remaining
+        }
+        else {
+            let padding = readCount % 4096
+            let remaining = length - completedReads
+            let thisBlockLen = Math.min(4096 - padding, length - completedReads)
+
+//            serial.println(`padding = ${padding}; remaining = ${remaining}`)
+//            serial.println(`block: (${thisBlockLen})[${[...Array(thisBlockLen).keys()].map(k => (sys.peek(-4097 - padding - k) & 255).toString(16).padStart(2,'0')).join()}]`)
+//            serial.println(`Reusing a block (${thisBlockLen}); readCount = ${readCount}, completedReads = ${completedReads}`)
+
+            // copy from read buffer to designated position
+            sys.memcpy(-4097 - padding, ptr + completedReads, thisBlockLen)
+
+            // increment readCount properly
+            readCount += thisBlockLen
+            completedReads += thisBlockLen
+        }
+    }
+
+    //serial.println(`END readBytes(${length}); readCount = ${readCount}\n`)
+
+    return ptr
+}
+
+function readInt() {
+    let b = readBytes(4)
+    let i = (sys.peek(b)) | (sys.peek(b+1) << 8) | (sys.peek(b+2) << 16) | (sys.peek(b+3) << 24)
+    sys.free(b)
+    return i
+}
+
+function readShort() {
+    let b = readBytes(2)
+    let i = (sys.peek(b)) | (sys.peek(b+1) << 8)
+    sys.free(b)
+    return i
+}
+
+function readFourCC() {
+    let b = readBytes(4)
+    let s = String.fromCharCode(sys.peek(b), sys.peek(b+1), sys.peek(b+2), sys.peek(b+3))
+    sys.free(b)
+    return s
+}
+
+function readString(length) {
+    let b = readBytes(length)
+    let s = ""
+    for (let k = 0; k < length; k++) {
+        s += String.fromCharCode(sys.peek(b + k))
+    }
+    sys.free(b)
+    return s
+}
+
+function skip(n) {
+    let b = readBytes(n)
+    if (b !== undefined) sys.free(b)
+}
+
+function getReadCount() {
+    return readCount
+}
+
+exports = {prepare, readBytes, readInt, readShort, readFourCC, readString, skip, getReadCount}