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Agon VDP Notes.txt
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Agon VDP Notes.txt
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1. VDP "ready" Signal
- After VDP has initialised, it will send Esc (27) to eZ80 via the UART
- Agon eZ80 firmware (MOS) boot code will wait for Esc from VDP
2. VDP comms
- VDP will send keypress codes to eZ80 via the UART
- VDP will send results of some commands to eZ80
- When a note is triggered VDU 23, 0, 5, channel, waveform, volume, freq, duration
- MOS can query VDP for:
- Cursor position VDU 23, 0, 2
- Char at position X, Y VDU 23, 0, 3, x, y
- Pixel at position X, Y VDU 23, 0, 4, x, y
- Mode information VDU 23, 0, 6
3. VDP Internal state
- Mode
- Screen buffer
- Current cursor pos
- Last keypress
4. VDP "commands" that need to be handled (for MOS display):
Absolute minimum
- char input commands (MOS putch() or printf())
- cursor movement commands, tab and backspace
- cls
- home
- mode
- set cursor pos (VDU 23, 0, 2)
In fact basic VDP emulation can be copied from VDP video.ino
2. MOS boot sequence ("debug" MOS (no autoexec.txt handling))
- Init interrupts, timers, SPI and UART0 (UART to VDP)
TMR2_CTL - port 86h
PB_DR - port 9Ah (SPI)
PB_DDR - port 9Bh
- Wait for Esc (27) from VDP UART
- print "Agon Quark MOS Version blah blah"
- Try to mount the SD card.
NB: eZ80F92 register (port) defines in ez80F92.inc
MOS writes 255 to 9B,
then 255 to 9F PC_DDR
then 255 to A3 PD_DDR
then 0 to 9C PB_ALT1
then 0 to A0 PC_ALT1
then 0 to A4 PD_ALT1
then 0 to 9D PB_ALT2
then 0 to A1 PC_ALT2
then 0 to A5 PD_ALT2
then 0 to 80 TMR0_CTL // Disable all timers
then 0 to 83 TMR1_CTL
then 0 to 86 TMR2_CTL
then 0 to 89 TMR3_CTL
then 0 to 8C TMR4_CTL
then 0 to 8F TMR5_CTL
then 0 to C1 UART0_IER
then 0 to D1 UART1_IER
then 0 to CB I2C_CTL
then 0 to FB FLASH_IRQ
then 4 to BA SPI_CTL
reads from port ED RTC_CTL
writes 0 to port ED RTC_CTL
writes 4 to port A8 CS0_LBR
write 11 to port A9 CS0_UBR
writes 1 to port F0 CS0_BMC
write 8 to port AA CS0_CTL
write 192 to port AB CS1_LBR
write 199 to port AC CS1_UBR
write 0 to port F1 CS1_BMC
write 8 to port AD CS1_CTL
write 128 to port AE
write 191 to port AF
write 0 to port F2
write 8 to port B0
write 3 to port B1
write 3 to port B2
write 130 to port F3
write 24 to port B3
write 0 to port F7 FLASH_ADDR_U
write 40 to port F8 FLASH_CTRL
write 183 to B5 RAM_ADDR_U
write 128 to B4 RAM_CTL
read from 9A PB_DR
write 2 to 9A PB_DR ( |= 2?)
read from 9B PB_DDR
write 2 to port 9B PB_DDR ( |= 2?)
read port 9C PB_ALT1
write 2 to 9C PB_ALT1 ( |= 2?)
read port 9D PB_ALT2
write 2 to 9D PB_ALT2 ( |= 2?)
init_timer2(1):
write 0 to 86 TMR2_CTL
write 4 to 88 TMR2_DR_H
write 128 to 87 TMR2_DR_L // Set timer reload to $480 (1152) - ~ 1ms ?
read from 86 TMR2_CTL
write 87 to 86 TMR2_CTL // $57 - Enable timer + reload, CLK/16, continuous mode, enable IRQ
init_spi():
read port 9A PB_DR
write 4 to 9A PB_DR |= BIT(2)
read port 9C PB_ALT1
write 0 to 9C PB_ALT1
read port 9D PB_ALT2
write 0 to 9D
read from 9B PB_DDR
write 0 to port 9B
read from 9A PB_DR
write 16 to 9A PB_DR ( |= 16?)
...
mode_spi(4):
write 0 to BA SPI_CTL Disable SPI
write 0 to B9 SPI_BRG_H
write 4 to B8 SPI_BRG_L Set SPI data rate divisor (bps)
write 48 to BA SPI_CTL Enable SPI
<pause> (while(i < 8000) i++;
init_UART0():
write 255 to A2 PD_DR
writw 255 to A3 PD_DDR
writw 0 to A4 PD_ALT1
write 0 to A5 PD_ALT2
wait_ESP32():
writes 3 to UART0 (C0)
writes 0 to C1 UART0_IER (disable interrupts?)
read from C3 UART0_LCTL (waiting for sent?)
write 0 to port C3
write 0 to port C4 UART0_MCTL
write 7 to port C2 UART0_IIR
write 1 to port C1 UART0_IER (enable interrupts?)
write 3 to C3 UART0_LCTL (8bit, N, 1 stop)
Writes text "Agon Quark MOS..." to VDP via serial (port C0)
read port 9A PB_DR PB3,4, 6, 7 are SD card (SPI)
write 16 to 9A PB_DR != 16 ?
Hangs in delayms() in MOS timer.c