It takes me longer than most people to get to this point as I'm a software person at heart and so blame that first ;)
I just happened to have a vintage 6522 VIA lying on my desk so I swapped the chips over. Joy! I was flipping bits like a demon. Naturally my thoughts turned to MMC...
10@=0
20!#208=!#208+3
30V=#B800
40W=#FFF4
50T=#80
60DIM LL(13),C(6)
70F.N=0TO13;LL(N)=#FFFF;N.N
80F.N=1TO2; DIM P(-1)
90P."PASS "N',$21
100[
110\ main
120:LL0 LDA @#0
130STA C+1; STA C+2; STA C+3; STA C+4
140LDA @#95; STA C+0
150JSR LL3
160LDA @#40+#0; JSR LL7
170LDA @CH"1"; SBC @0; JMP W
180\ select card
190:LL1 LDA @0; STA V; RTS
200\ deselect card
210:LL2 LDA @#20; STA V; RTS
220\ init hw and go spi
230:LL3 LDA @0; STA V+#C
240LDA @#FE; STA V+2
250LDA @#20; STA V
260LDY @10
270:LL4 LDA @#FF; JSR LL5; DEY; BNE LL4
280RTS
290\ xferbyte
300:LL5 STX T+0; STY T+1; LDY @8
310:LL6 PHA; AND @#80; STA V
320ORA @#40; STA V
330LDX V; AND @#BF; STA V
340TXA; ROR A
350PLA; ROL A
360DEY; BNE LL6
370PHA; JSR #F7FA; PLA
380LDY T+1; LDX T+0;
390RTS
400\ command
410:LL7 STA C+5; LDY @5
420:LL8 LDA C,Y; JSR LL5; DEY; BPL LL8
430:LL9 LDA @#FF; JSR LL5; AND @#FF; CLC; BPL LL10
440DEY; BNE LL9;
450SEC
460:LL10 RTS
470]
480P.$6
490NE.N
500END
If you're an ex-atommer or you've been around BBC micros you might recognise this. If you don't then I can tell you it's some Atom basic with inline assembler. The Atom's Basic dialect was hard on the eyes but lightning fast. By the standards of the day, naturally ;)
The built-in assembler gave the user of this machine an instant boost when learning to program. No fussing with 3rd party apps, loading the assembler or machine code, or the attendant problems with cassettes. Turn on. Assemble. Bam! (Which is as it happens almost quite literally what happened to my 1st Atom over 20 years ago...) Now if only it was that easy for the kids of today - it was much better in the old days - I remember when all this was fields etc. etc.
The above listing is code to bit-bang SPI to an MMC card attached via the simplest of hardware harnesses to the rear expansion connector of the Atom. I'm looking at making a ROM based solution that hooks into the OS's filing system vectors. It's all quite primitive at the moment but I'm hoping it'll solidify. Get in touch if you have any experience of developing this kind of Atom program. I'd love to talk to you.
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