izapple2/component/mc6845.go
2021-03-14 22:38:41 +01:00

118 lines
3.2 KiB
Go

package component
/*
MC6845 CRT Controller
See:
Motorola MC6845 datasheet
Pins:
RW, RS, D0-D7: Read() and Write()
MA0-13, RA04, CURSOR, DE: MC6845RasterCallBack()
*/
type MC6845 struct {
reg [18]uint8 // Internal registers R0 to R17
sel uint8 // Selected address register AR
}
func (m *MC6845) Read(rs bool) uint8 {
if !rs {
// AR is not readable
return 0x00
} else if m.sel >= 14 && m.sel <= 17 {
// Only R14 to R17 are readable
// Should we mask R14 and R16?
return m.reg[m.sel]
}
return 0x00
}
func (m *MC6845) Write(rs bool, value uint8) {
if !rs {
// AR is 5 bits
// What happens if AR > 17 ?
m.sel = value & 0x1f
} else if m.sel <= 15 {
// R0 to R15 are writable
m.reg[m.sel] = value
//fmt.Printf("Set %v to %v\n", m.sel, value)
}
}
func (m *MC6845) ImageData() MC6845ImageData {
var data MC6845ImageData
data.firstChar = uint16(m.reg[12]&0x3f)<<8 + uint16(m.reg[13])
data.charLines = (m.reg[9] + 1) & 0x1f
data.columns = m.reg[1]
data.lines = m.reg[6] & 0x7f
data.adjustLines = m.reg[5] & 0x1f
data.cursorPos = uint16(m.reg[14]&0x3f)<<8 + uint16(m.reg[15])
data.cursorStart = m.reg[10] & 0x1f
data.cursorEnd = m.reg[11] & 0x1f
data.cursorMode = (m.reg[10] >> 5) & 0x03 // Bit 6 and 5
return data
}
const (
MC6845CursorFixed = uint8(0)
MC6845CursorNone = uint8(1)
MC6845CursorFast = uint8(2)
MC6845CursorSlow = uint8(3)
)
type MC6845ImageData struct {
firstChar uint16 // 14 bits, address of the firt char on the first line
charLines uint8 // 5 bits, lines par character
columns uint8 // 8 bits, chars per line
lines uint8 // 7 bits, char lines per screen
adjustLines uint8 // 5 bits, extra blank lines
cursorPos uint16 // 14 bits, address? of the cursor position
cursorStart uint8 // 5 bits, cursor starting char row
cursorEnd uint8 // 5 bits, cursor ending char row
cursorMode uint8 // 2 bits, cursor mode
}
func (data *MC6845ImageData) DisplayedWidthHeight(charWidth uint8) (int, int) {
return int(data.columns) * int(charWidth),
int(data.lines)*int(data.charLines) + int(data.adjustLines)
}
type MC6845RasterCallBack func(address uint16, charLine uint8, // Lookup in char ROM
cursorMode uint8, displayEnable bool, // Modifiers
column uint8, y int) // Position in screen
func (data *MC6845ImageData) IterateScreen(callBack MC6845RasterCallBack) {
lineAddress := data.firstChar
y := 0
var address uint16
for line := uint8(0); line < data.lines; line++ {
for charLine := uint8(0); charLine < data.charLines; charLine++ {
address = lineAddress // Back to the first char of the line
for column := uint8(0); column < data.columns; column++ {
cursorMode := MC6845CursorNone
isCursor := (address == data.cursorPos) &&
(charLine >= data.cursorStart) &&
(charLine <= data.cursorEnd)
if isCursor {
cursorMode = data.cursorMode
}
callBack(address, charLine, cursorMode, true, column, y)
address = (address + 1) & 0x3fff // 14 bits
}
y++
}
lineAddress = address
}
for adjust := uint8(0); adjust <= data.adjustLines; adjust++ {
for column := uint8(0); column < data.columns; column++ {
callBack(0, 0, MC6845CursorNone, false, column, y) // lines with display not enabled
}
y++
}
}