From c255903323d3055b93b3210e714f73770689aded Mon Sep 17 00:00:00 2001 From: Clanmaster21 Date: Thu, 17 Oct 2019 20:20:13 +0100 Subject: [PATCH] Saved some bytes in parseHexPair and sdc I replaced some doubled up nops with pushes and pops again, saving two bytes. There was also a nop in a loop that didn't look necessary, since the jump back to the top of the loop is already 13 cycles, so way more than 80 cycles are spent in that loop anyway. I reworked things a little in parseHexPair and saved 5 bytes and 6 cycles, with more cycles saved in error cases. --- kernel/parse.asm | 80 ++++++++++++++++++++++-------------------------- kernel/sdc.asm | 11 +++---- 2 files changed, 40 insertions(+), 51 deletions(-) diff --git a/kernel/parse.asm b/kernel/parse.asm index 1bd81b2..3935e31 100644 --- a/kernel/parse.asm +++ b/kernel/parse.asm @@ -11,26 +11,16 @@ ; On success, the carry flag is reset. On error, it is set. parseHex: ; First, let's see if we have an easy 0-9 case - cp '0' - jr c, .error ; if < '0', we have a problem - cp '9'+1 - jr nc, .alpha ; if >= '9'+1, we might have alpha - ; We are in the 0-9 range - sub '0' ; C is clear - ret + + add a, 0xc6 ; maps '0'-'9' onto 0xf6-0xff + sub 0xf6 ; maps to 0-9 and carries if not a digit + ret nc -.alpha: - call upcase - cp 'A' - jr c, .error ; if < 'A', we have a problem - cp 'F'+1 - jr nc, .error ; if >= 'F', we have a problem - ; We have alpha. - sub 'A'-10 ; C is clear - ret - -.error: - scf + and 0xdf ; converts lowercase to uppercase + add a, 0xe9 ; map 0x11-x017 onto 0xFA - 0xFF + sub 0xfa ; map onto 0-6 + ret c + add a, 10 ; C is clear, map back to 0xA-0xF ret ; Parses 2 characters of the string pointed to by HL and returns the numerical @@ -39,34 +29,35 @@ parseHex: ; HL is set to point to the last char of the pair. ; ; On success, the carry flag is reset. On error, it is set. -parseHexPair: - push bc - ld a, (hl) - call parseHex - jr c, .end ; error? goto end, keeping the C flag on - rla \ rla \ rla \ rla ; let's push this in MSB - ld b, a - inc hl - ld a, (hl) - cp 0x21 - jr c, .single ; special char? single digit - call parseHex - jr c, .end ; error? - or b ; join left-shifted + new. we're done! - ; C flag was set on parseHex and is necessarily clear at this point - jr .end -.single: - ; If we have a single digit, our result is already stored in B, but - ; we have to right-shift it back. - ld a, b - and 0xf0 - rra \ rra \ rra \ rra - dec hl +parseHexPair: ; 31 bytes, 78 cycles + ld a, (hl) + call parseHex + ret c ; faster and smaller than a conditional jump +; by delaying this push, we can use a conditional return above + push bc + ld b, a + inc hl + ld a, (hl) + cp 0x21 + jr c, .single + call parseHex + jr c, .end + ld c, a + ld a, b + ; by delaying shifting until the end, we save bytes in the single case. + rla \ rla \ rla \ rla + or c -.end: - pop bc + .end: + pop bc + ret + + .single: ;53 cycles if single + ld a, b + dec hl + pop bc ret ; Parse arguments at (HL) with specifiers at (DE) into (IX). @@ -86,6 +77,7 @@ parseHexPair: ; be placed in the next two bytes. This has to be the ; last argument of the list and it stops parsing. ; Sets A to nonzero if there was an error during parsing, zero otherwise. + parseArgs: push bc push de diff --git a/kernel/sdc.asm b/kernel/sdc.asm index 6cd00c6..1b63214 100644 --- a/kernel/sdc.asm +++ b/kernel/sdc.asm @@ -85,14 +85,13 @@ ; *** Code *** ; Wake the SD card up. After power up, a SD card has to receive at least 74 -; dummy clocks with CS and DI high. We send 80. +; dummy clocks with CS and DI high. We send (way more than) 80. sdcWakeUp: out (SDC_PORT_CSHIGH), a - ld b, 10 ; 10 * 8 == 80 + ld b, 10 ; 10 * 11 == 110 ld a, 0xff .loop: out (SDC_PORT_SPI), a - nop djnz .loop ret @@ -100,11 +99,9 @@ sdcWakeUp: ; is placed in A. sdcSendRecv: out (SDC_PORT_SPI), a - nop - nop + push hl ; nop, pairs with pop later in a, (SDC_PORT_SPI) - nop - nop + pop hl ; nop, pairs with earlier push ret sdcIdle: