Alphatronic P2 speed follow-up 2
- Memory map
- The adjusted “Tone Generator” v4
- Upper memory
This is one additional follow up. As figured out in the last post, the used memory chips (ROM and RAM) on the CPU card are likely fast enough to be used without a wait state. So the idea is, to run my tone generator and maybe the floppy drive rotation measurement in the RAM on the CPU card.
The RAM on the CPU card is 1kB. This should be big enough for my small programs. However, this RAM is used by the MOS (Mikrocomputer Operating System), so overwriting data in there might destroy some data structures. But that’s ok, then I just need to reset the whole PC again, and it should work again.
The memory map of the Alphatronic P2 is given in the following picture:
The 1kB RAM on the CPU card begins at address 0x1800 and ends with 0x1BFF. The range from 0x1C00 to 0x1FFF seems to be unmapped and unusable.
The “Tone Generator” machine program requires 59 bytes (0x3B). The stack of the MOS starts at 0x1980 and grows up to 0x1800. So let’s just use the range 0x1800 to 0x183B for our program…
The adjusted “Tone Generator” v4
We need to adjust the program from Measuring CPU speed and change the jumps to be in the correct address space. The counters stay as they are - so the loop should be repeated 243 (0xF3) times.
; address machine code mnemonic comments 1800 06 05 MVI B, 5H 1802 G 0E DC MVI C, DCH ; 0xDC=220 1804 C 3E 01 MVI A, 1H 1806 D3 12 OUT 12H ; 0x12=18 1808 16 F3 MVI D, F3H ; 0xF3=243 180A A 15 DCR D 180B C2 0A 18 JNZ A ; A -> 0x180A 180E 3E 00 MVI A, 0H 1810 D3 12 OUT 12H ; 0x12=18 1812 16 F3 MVI D, F3H ; 0xF3=243 1814 B 15 DCR D 1815 C2 14 18 JNZ B ; B -> 0x1814 1818 0D DCR C 1819 C2 04 18 JNZ C ; C -> 0x1804 181C 0E DC MVI C, DCH ; 0xDC=220 181E F 3E 00 MVI A, 0H 1820 D3 12 OUT 12H ; 0x12=18 1822 16 F3 MVI D, F3H ; 0xF3=243 1824 D 15 DCR D 1825 C2 24 18 JNZ D ; D -> 0x1824 1828 3E 00 MVI A, 0H 182A D3 12 OUT 12H ; 0x12=18 182C 16 F3 MVI D, F3H ; 0xF3=243 182E E 15 DCR D 182F C2 2E 18 JNZ E ; E -> 0x182E 1832 0D DCR C 1833 C2 1E 18 JNZ F ; F -> 0x181E 1836 05 DCR B 1837 C2 02 18 JNZ G ; G -> 0x1802 183A C9 RET
The BASIC program to load this also looks a bit different. We don’t need the
anymore, since we don’t put it into the memory space of the BASIC interpreter anymore. The
statement made space for us by moving some data structure of the BASIC interpreter out of the way.
100 PRINT "Tone Generator V4" 110 I=&H1800 120 READ D$ 130 D=VAL("&H"+D$) 140 IF D>255 THEN GOTO 500 150 POKE I,D 160 I=I+1 170 GOTO 120 200 DATA 06,05,0E,DC,3E,01,D3,12,16,F3,15,C2,0A,18,3E,00,D3,12 210 DATA 16,F3,15,C2,14,18,0D,C2,04,18,0E,DC,3E,00,D3,12,16,F3 220 DATA 15,C2,24,18,3E,00,D3,12,16,F3,15,C2,2E,18,0D,C2,1E,18 230 DATA 05,C2,02,18,C9 490 DATA E0F 500 I=&H1800 510 CALL I
The resulting video:
If you analyze the audio, you’ll find that the tones are now about 1 second apart and closer to 440 Hz.
Bonus: Floppy Drive rotation
The original program from Measuring Floppy Drive rotation speed - Part 2 also needs some adjustments. It’s size is even smaller, it only needs 30 (0x1E) bytes. Here it is:
ORG 1800H PUBLIC READ_INDEX_DURATION 1800' 3E D4 READ_INDEX_DURATION: MVI A,D4H ;FORCE-INTERRUPT command with IP (index pulse) 1802' D3 50 OUT 50H ;execute command 1804' 06 40 MVI B,40H ;Mask for index detected flag in status register 1806' 11 0000 LXI D,0 ;init counter in D 1809' DB 50 IN 50H ;reading the command register?? apparently clearing the IRQ flag 180B' DB 54 LOOP1: IN 54H ;reading status register into A 180D' A0 ANA B ;check if index is set 180E' CA 0B18' JZ LOOP1 ;if no index yet, busy wait... 1811' DB 50 IN 50H ;clearing the INDEX flag for next index detection 1813' 13 LOOP2: INX D ;counting now... 1814' DB 54 IN 54H ;reading status register into A 1816' A0 ANA B ;check if index is set 1817' CA 1318' JZ LOOP2 ;jump back, if no index and keep counting 181A' 73 MOV M,E ;copy counter (low Byte) to memory at [H] 181B' 23 INX H ; 181C' 72 MOV M,D ;copy counter (high Byte) to memory at [H] 181D' C9 RET
And the BASIC program:
100 '************** DRIVEROT4 110 DEFINT D 120 GOSUB 500 130 PRINT"In the last used drive a floppy has to be inserted!" 140 INPUT"How many measurements should be taken?"; COUNT 150 DIM DAT%(COUNT) 160 FOR D=0 TO COUNT-1 170 PRINT" Start measurement ";D 180 CALL RID(LOOPS%) 190 DAT%(D)=LOOPS% 195 PRINT" result:";D;"->";DAT%(D) 200 NEXT 210 PRINT"Data ready" 220 MIN=DAT(0) :MAX=MIN :SUM=0 230 FOR D=0 TO COUNT-1 240 IF DAT(D)<MIN THEN MIN=DAT(D) 250 IF DAT(D)>MAX THEN MAX=DAT(D) 260 SUM=SUM+DAT(D) 270 NEXT 280 MEAN=SUM/COUNT 290 LPS=103448! 'loops per second: 3 MHz/29 cycles - dur. of one loop 300 RPM=INT(60*LPS/MEAN+.5) 310 DIF=MAX-MIN 320 PRINT" Minimum:";MIN/LPS;"s" 330 PRINT" Maximum:";MAX/LPS;"s" 340 PRINT" Mean:";MEAN/LPS;"s" 350 PRINT"Rotations:";RPM;"rpm" 360 PRINT" Accuracy:";DIF*1000/LPS;"ms" 370 END 500 ' Machine program RID (=read_index_duration) 510 I=&H1800 520 RID=&H1800 530 READ D$ 540 D=VAL("&H"+D$) 550 IF D>255 THEN RETURN 560 POKE I,D 570 I=I+1 580 GOTO 530 590 DATA 3E,D4,D3,50,06,40,11,00,00,DB,50,DB,54 600 DATA A0,CA,0B,18,DB,50,13,DB,54,A0,CA,13,18 610 DATA 73,23,72,C9,E0F
The result is pretty impressive:
RUN In the last used drive a floppy has to be inserted! How many measurements should be taken?? 10 Start measurement 0 result: 0 -> 20287 Start measurement 1 result: 1 -> 20222 Start measurement 2 result: 2 -> 20552 Start measurement 3 result: 3 -> 20778 Start measurement 4 result: 4 -> 20696 Start measurement 5 result: 5 -> 20396 Start measurement 6 result: 6 -> 20640 Start measurement 7 result: 7 -> 20652 Start measurement 8 result: 8 -> 20389 Start measurement 9 result: 9 -> 20443 Data ready Minimum: .19548 s Maximum: .200855 s Mean: .19822 s Rotations: 303 rpm Accuracy: 5.37468 ms Ok
This was the measurement on the real floppy drive: 303rpm. That’s basically valid. I also measured it on the GoTek floppy emulator: 310rpm. A bit too high, it should be exactly 300rpm. But ok.
I’ve had a close look again at the memory card and I’ve now found a connection to the READY-signal. Although I don’t know exactly, how it is connected - at least it seems to be used.
The card uses a 8202 Dynamic RAM controller to refresh the 24 chips on the left. Each of these chips is a 4116 and stores 16384 bit of memory (2048 bytes). In total, this card provides 48kB of RAM.
There is another card, that contains 16kB of RAM. So it seems that my Alphatronic is not the model P2 but the model P2U. This has the ability to use full 64kB of RAM with the help of bank switching.
The memory map explains, that the 48kB card is mapped from 0000 to BFFF. However, the lower part from 0000 to 3FFF is used by the ROM chips to provide the MOS. The 16kB card is added from C000 to FFFF. With the bank switch one can remove the MOS and use the lower part of the 48kB card from 0000 to 3FFF.
So it turns out, that my “slow” program actually ran from the 16kB card. This card however doesn’t have a dynamic memory controller and no connection to the READY signal.
That proves, that the memory on the CPU card doesn’t use any wait states and the programs are actually correct. But using the upper memory slows down the Alphatronic P2. Or P2U?
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