Added MegaFlash clock support

README.md

@@ -16,6 +16,7 @@ An internal clock on the Apple side is required for this functionality to be ena
  2. NoSlotClock
  3. Thunderclock
  4. ROMX family
+ 5. MegaFlash (Apple IIc/IIc+ with [MegaFlash](https://github.com/ThomasFok/MegaFlash))
 
 The reason why SPF can't/doesn't use the built-in ProDOS clock interface is it only gives information to the minute
 resolution - and we need seconds.  (More resolution would be nice, but seconds seems to be the best we can hope for in the universe of Apple II clocks.)

doc/MegaFlash_Clock.md

@@ -0,0 +1,75 @@
+# MegaFlash Clock Support - Design Notes
+
+This document captures the reasoning and design decisions behind adding MegaFlash clock support to SPF.
+
+## Background
+
+**MegaFlash** is an internal storage device for Apple IIc/IIc+ computers ([ThomasFok/MegaFlash](https://github.com/ThomasFok/MegaFlash)). It includes:
+- Flash storage (128MB/256MB)
+- Real-time clock with ProDOS driver
+- NTP time sync capability
+
+SPF's benchmark feature requires second-resolution timing. The standard ProDOS clock interface only provides minute resolution, so SPF uses a compatibility layer that detects and uses various hardware clocks directly.
+
+## Research Process
+
+1. **Identification**: MegaFlash was identified from the GitHub repo. The README lists "Real Time Clock with ProDOS clock driver" as a feature.
+
+2. **Architecture**: MegaFlash is IIc/IIc+ only—it replaces the system ROM. Unlike slot-based cards (Thunderclock), it uses fixed I/O addresses $C0C0-$C0C3. Activation is handled in MegaFlash ROM; SPF does not perform the magic address sequence—it only checks for presence and reads the time.
+
+3. **API Discovery**: From `common/defines.inc` and `firmware/megaflash.s`:
+   - I/O: `cmdreg`/`statusreg`=$C0C0, `paramreg`=$C0C1, `datareg`=$C0C2, `idreg`=$C0C3
+   - `CMD_GETDEVINFO` ($10) returns signature bytes $88, $74 in paramreg for detection
+   - `CMD_GETPRODOS25TIME` ($18) returns 6-byte ProDOS 2.5 timestamp (includes seconds)
+
+4. **Time Format**: From `pico/rtc.c` and `pico/cmdhandler.c`:
+   - ProDOS legacy (4 bytes): date_lo, date_hi, minute, hour — **no seconds**
+   - ProDOS 2.5 (6 bytes): t4ms, second, time_lo, time_hi, date_lo, date_hi
+   - The time word: `time = mday<<11 | hour<<6 | min` (min=bits 0-5, hour=bits 6-10, mday=bits 11-15)
+
+## Design Decisions
+
+### 1. Detection Order
+
+MegaFlash is checked **after** ROMX and **before** slotted clocks. Rationale:
+- IIgs and NoSlotClock are checked first (common)
+- ROMX is another "replacement" device
+- MegaFlash (IIc-specific) before generic slotted clocks
+- Thunderclock remains last for slot-based detection
+
+### 2. ProDOS 2.5 vs ProDOS Legacy Format
+
+We use `CMD_GETPRODOS25TIME` exclusively because:
+- SPF needs **seconds** for elapsed-time benchmarks
+- ProDOS legacy format only provides hour and minute
+- ProDOS 2.5 format includes the second byte
+
+### 3. Bit Extraction for Hour and Minute
+
+The time word layout: `[mday:5][hour:5][min:6]`
+
+- **Minutes**: `time & $3F` (low 6 bits)
+- **Hours**: `(time >> 6) & $1F` (next 5 bits)
+
+Decomposed for 6502:
+- `hour_lo2 = (time_lo >> 6)` — bits 6–7 of time_lo become bits 0–1 of hour
+- `hour_hi3 = (time_hi & $07) << 2` — bits 0–2 of time_hi (time bits 8–10) become bits 2–4 of hour
+- `hour = hour_lo2 | hour_hi3` (5 bits, 0–23)
+
+### 4. Hundredths of Seconds
+
+MegaFlash provides `t4ms` (0–249, units of 4ms), so hundredths could be approximated. We use 0 for consistency with other clocks (GS, ROMX, Thunderclock) that don't expose sub-second resolution.
+
+### 5. Error Handling
+
+- **Detection timeout**: If the busy flag stays set for 100 polls, we assume no MegaFlash.
+- **GetTime error**: If the status register error bit is set after the time command, we skip updating TimeNow and return (leaving prior values).
+
+### 6. RTC Not Initialized
+
+If MegaFlash's RTC has never been set (no NTP, no manual set), the firmware returns all zeros. SPF will show 00:00:00 and benchmarks would report ~0 elapsed time. This is a user configuration issue; we document it in the README.
+
+## Implementation Notes
+
+- **MFTime buffer**: 4 bytes for temp storage during extraction. [0] holds intermediate hour bits, [1]=sec, [2–3]=time word.
+- **Activation**: Handled in MegaFlash ROM; SPF does not perform the magic address sequence.

src/prodos/gettime.asm

@@ -26,6 +26,8 @@ InitTime:
 	bcc FoundClockNoSlot
 	jsr CheckForROMX
 	bcc FoundClockROMX
+	jsr CheckForMegaFlash
+	bcc FoundClockMegaFlash
 	jsr CheckForSlottedClocks
 	rts
 
@@ -59,6 +61,16 @@ FoundClockROMX:
 	sta GetTime+2
 	rts
 
+FoundClockMegaFlash:
+;---------------------------------------------------------
+; Patch the entry point of GetTime to the MegaFlash version
+;---------------------------------------------------------
+	lda #<GetTimeMegaFlash
+	sta GetTime+1
+	lda #>GetTimeMegaFlash
+	sta GetTime+2
+	rts
+
 GetTime:
 	jsr $0000
 	rts
@@ -176,6 +188,101 @@ GetTimeROMX:
 	sta TimeNow+3
 	rts
 
+;---------------------------------------------------------
+; MegaFlash clock support (Apple IIc/IIc+ with MegaFlash)
+; https://github.com/ThomasFok/MegaFlash
+;
+; Design notes: doc/MegaFlash_Clock.md
+;
+; Activation is handled in MegaFlash ROM; we only check presence and read time.
+; Detection: CMD_GETDEVINFO returns signature $88,$74 in paramreg.
+;
+; GetTime: CMD_GETPRODOS25TIME returns 6 bytes. Time word (bytes 2-3)
+; packs [mday:5][hour:5][min:6]; we extract hour=(time>>6)&$1F,
+; min=time&$3F. Byte 1 = seconds.
+;---------------------------------------------------------
+MF_CMDSTATUS	= $C0C0
+MF_PARAM	= $C0C1
+MF_CMD_GETDEVINFO	= $10
+MF_CMD_GETPRODOS25TIME	= $18
+MF_SIGNATURE1	= $88
+MF_SIGNATURE2	= $74
+
+CheckForMegaFlash:
+	; ROM activates MegaFlash if present; just check for presence
+	; Send GETDEVINFO command
+	lda #MF_CMD_GETDEVINFO
+	sta MF_CMDSTATUS
+	; Wait for busy to clear (with timeout)
+	ldx #100
+:	bit MF_CMDSTATUS
+	bpl :+
+	dex
+	bne :-
+	; Timeout - MegaFlash not present
+	sec
+	rts
+:	; Check for error (bit 6)
+	bvs CheckMegaFlashFail
+	; Verify signature bytes
+	lda MF_PARAM
+	cmp #MF_SIGNATURE1
+	bne CheckMegaFlashFail
+	lda MF_PARAM
+	cmp #MF_SIGNATURE2
+	bne CheckMegaFlashFail
+	; MegaFlash found
+	clc
+	rts
+CheckMegaFlashFail:
+	sec
+	rts
+
+GetTimeMegaFlash:
+	; Request ProDOS 2.5 format time (includes seconds)
+	lda #MF_CMD_GETPRODOS25TIME
+	sta MF_CMDSTATUS
+	; Wait for completion
+:	bit MF_CMDSTATUS
+	bmi :-
+	bvs GetTimeMFDone	; Error - skip update
+	; Read 6 bytes: [0]=4ms units, [1]=sec, [2-3]=time word, [4-5]=date
+	lda MF_PARAM		; t4ms - discard
+	lda MF_PARAM		; seconds
+	sta MFTime+1
+	lda MF_PARAM		; time lo
+	sta MFTime+2
+	lda MF_PARAM		; time hi
+	sta MFTime+3
+	lda MF_PARAM		; date lo - discard
+	lda MF_PARAM		; date hi - discard
+	; Extract: min = time & $3F, hour = (time >> 6) & $1F
+	lda MFTime+2
+	and #$3F
+	sta TimeNow+1		; Minutes
+	lda MFTime+2
+	lsr a
+	lsr a
+	lsr a
+	lsr a
+	lsr a
+	lsr a
+	sta MFTime+0		; temp: hour low 2 bits
+	lda MFTime+3
+	and #$07			; hour bits from high byte
+	asl a
+	asl a
+	ora MFTime+0
+	sta TimeNow		; Hours
+	lda MFTime+1
+	sta TimeNow+2		; Seconds
+	lda #$00
+	sta TimeNow+3		; Hundredths (MegaFlash has 4ms, we use 0 for simplicity)
+GetTimeMFDone:
+	rts
+
+MFTime:	.res 4		; Temp: [0]=hour bits, [1]=sec, [2]=time_lo, [3]=time_hi
+
 CheckForNoSlotClock:
 	jsr PrepNoSlotClock	; Prepare the driver
 	jsr NSCEntry		; Call it to get the time