106 lines
2.9 KiB
Go
106 lines
2.9 KiB
Go
package component
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/*
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MC6845 CRT Controller
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See:
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Motorola MC6845 datasheet
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Pins:
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RW, RS, D0-D7: Read() and Write()
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MA0-13, RA04, CURSOR, DE: MC6845RasterCallBack()
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*/
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type MC6845 struct {
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reg [18]uint8 // Internal registers R0 to R17
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sel uint8 // Selected address register AR
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}
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func (m *MC6845) Read(rs bool) uint8 {
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if !rs {
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// AR is not readable
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return 0x00
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} else if m.sel >= 14 && m.sel <= 17 {
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// Only R14 to R17 are readable
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// Should we mask R14 and R16?
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return m.reg[m.sel]
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}
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return 0x00
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}
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func (m *MC6845) Write(rs bool, value uint8) {
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if !rs {
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// AR is 5 bits
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// What happens if AR > 17 ?
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m.sel = value & 0x1f
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} else if m.sel <= 15 {
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// R0 to R15 are writable
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m.reg[m.sel] = value
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//fmt.Printf("Set %v to %v\n", m.sel, value)
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}
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}
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func (m *MC6845) ImageData() MC6845ImageData {
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var data MC6845ImageData
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data.firstChar = uint16(m.reg[12]&0x3f)<<8 + uint16(m.reg[13])
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data.charLines = (m.reg[9] + 1) & 0x1f
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data.columns = m.reg[1]
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data.lines = m.reg[6] & 0x7f
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data.adjustLines = m.reg[5] & 0x1f
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data.cursorPos = uint16(m.reg[14]&0x3f)<<8 + uint16(m.reg[15])
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data.cursorStart = m.reg[10] & 0x1f
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data.cursorEnd = m.reg[11] & 0x1f
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// cursor mode is on bits 6 and 5 of R10
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return data
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}
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type MC6845ImageData struct {
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firstChar uint16 // 14 bits, address of the firt char on the first line
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charLines uint8 // 5 bits, lines par character
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columns uint8 // 8 bits, chars per line
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lines uint8 // 7 bits, char lines per screen
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adjustLines uint8 // 5 bits, extra blank lines
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cursorPos uint16 // 14 bits, address? of the cursor position
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cursorStart uint8 // 5 bits, cursor starting char row
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cursorEnd uint8 // 5 bits, cursos ending char row
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// cursor mode
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}
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func (data *MC6845ImageData) DisplayedWidthHeight(charWidth uint8) (int, int) {
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return int(data.columns) * int(charWidth),
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int(data.lines)*int(data.charLines) + int(data.adjustLines)
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}
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type MC6845RasterCallBack func(address uint16, charLine uint8, // Lookup in char ROM
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cursor bool, displayEnable bool, // Modifiers
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column uint8, y int) // Position in screen
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func (data *MC6845ImageData) IterateScreen(callBack MC6845RasterCallBack) {
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lineAddress := data.firstChar
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y := 0
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var address uint16
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for line := uint8(0); line < data.lines; line++ {
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for charLine := uint8(0); charLine < data.charLines; charLine++ {
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address = lineAddress // Back to the first char of the line
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for column := uint8(0); column < data.columns; column++ {
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isCursor := (address == data.cursorPos) &&
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(charLine >= data.cursorStart) &&
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(charLine <= data.cursorEnd)
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callBack(address, charLine, isCursor, true, column, y)
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address = (address + 1) & 0x3fff // 14 bits
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}
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y++
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}
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lineAddress = address
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}
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for adjust := uint8(0); adjust <= data.adjustLines; adjust++ {
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for column := uint8(0); column < data.columns; column++ {
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callBack(0, 0, false, false, column, y) // lines with display not enabled
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}
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y++
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}
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}
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