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Merged
merged 2 commits into from
Apr 21, 2022
Merged

ws2812: write inline assembly using C instead of Go #401

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c4d1591
ws2812: write inline assembly using C instead of Go
aykevl Apr 14, 2022
18fabe3
ws2812: convert AVR assembly to C inline assembly
aykevl Apr 14, 2022
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2 changes: 2 additions & 0 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,8 @@ smoke-test:
@md5sum ./build/test.hex
tinygo build -size short -o ./build/test.hex -target=circuitplay-express ./examples/ws2812
@md5sum ./build/test.hex
tinygo build -size short -o ./build/test.bin -target=m5stamp-c3 ./examples/ws2812
@md5sum ./build/test.bin
tinygo build -size short -o ./build/test.hex -target=feather-nrf52840 ./examples/is31fl3731/main.go
@md5sum ./build/test.hex
ifneq ($(AVR), 0)
Expand Down
105 changes: 68 additions & 37 deletions ws2812/gen-ws2812.go
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Original file line number Diff line number Diff line change
Expand Up @@ -60,21 +60,21 @@ var architectures = map[string]architectureImpl{
minBaseCyclesT1H: 1 + 1 + 2, // shift + branch (taken) + store
maxBaseCyclesT1H: 1 + 3 + 2, // shift + branch (taken) + store
minBaseCyclesTLD: 1 + 2 + 2, // subtraction + branch x2 + store (in next cycle)
valueTemplate: "uint32(c) << 24",
valueTemplate: "(uint32_t)c << 24",
template: `
1: @ send_bit
str {maskSet}, {portSet} @ [2] T0H and T0L start here
str %[maskSet], %[portSet] @ [2] T0H and T0L start here
@DELAY1
lsls {value}, #1 @ [1]
bcs.n 2f @ [1/3] skip_store
str {maskClear}, {portClear} @ [2] T0H -> T0L transition
lsls %[value], #1 @ [1]
bcs.n 2f @ [1/3] skip_store
str %[maskClear], %[portClear] @ [2] T0H -> T0L transition
2: @ skip_store
@DELAY2
str {maskClear}, {portClear} @ [2] T1H -> T1L transition
str %[maskClear], %[portClear] @ [2] T1H -> T1L transition
@DELAY3
subs {i}, #1 @ [1]
beq.n 3f @ [1/3] end
b 1b @ [1/3] send_bit
subs %[i], #1 @ [1]
beq.n 3f @ [1/3] end
b 1b @ [1/3] send_bit
3: @ end
`,
},
Expand All @@ -90,25 +90,25 @@ var architectures = map[string]architectureImpl{
minBaseCyclesT1H: 1 + 1 + 1, // shift + branch (taken) + store
maxBaseCyclesT1H: 1 + 3 + 1, // shift + branch (taken) + store
minBaseCyclesTLD: 1 + 1 + 1, // subtraction + branch + store (in next cycle)
valueTemplate: "uint32(c) << 23",
valueTemplate: "(uint32_t)c << 23",
template: `
1: // send_bit
sw {maskSet}, {portSet} // [1] T0H and T0L start here
sw %[maskSet], %[portSet] // [1] T0H and T0L start here
@DELAY1
slli {value}, {value}, 1 // [1] shift value left by 1
bltz {value}, 2f // [1/3] skip_store
sw {maskClear}, {portClear} // [1] T0H -> T0L transition
slli %[value], %[value], 1 // [1] shift value left by 1
bltz %[value], 2f // [1/3] skip_store
sw %[maskClear], %[portClear] // [1] T0H -> T0L transition
2: // skip_store
@DELAY2
sw {maskClear}, {portClear} // [1] T1H -> T1L transition
sw %[maskClear], %[portClear] // [1] T1H -> T1L transition
@DELAY3
addi {i}, {i}, -1 // [1]
bnez {i}, 1b // [1/3] send_bit
addi %[i], %[i], -1 // [1]
bnez %[i], 1b // [1/3] send_bit
`,
},
}

func writeImplementation(f *os.File, arch string, megahertz int) error {
func writeCAssembly(f *os.File, arch string, megahertz int) error {
cycleTimeNS := 1 / float64(megahertz)
// These timings are taken from the table "Updated simplified timing
// constraints for NeoPixel strings" at:
Expand Down Expand Up @@ -209,30 +209,51 @@ func writeImplementation(f *os.File, arch string, megahertz int) error {
// ignore I/O errors.
buf := &bytes.Buffer{}
fmt.Fprintf(buf, "\n")
fmt.Fprintf(buf, "func (d Device) writeByte%d(c byte) {\n", megahertz)
fmt.Fprintf(buf, " portSet, maskSet := d.Pin.PortMaskSet()\n")
fmt.Fprintf(buf, " portClear, maskClear := d.Pin.PortMaskClear()\n")
fmt.Fprintf(buf, "\n")
fmt.Fprintf(buf, "__attribute__((always_inline))\nvoid ws2812_writeByte%d(char c, uint32_t *portSet, uint32_t *portClear, uint32_t maskSet, uint32_t maskClear) {\n", megahertz)
fmt.Fprintf(buf, " // Timings:\n")
fmt.Fprintf(buf, " // T0H: %2d - %2d cycles or %.1fns - %.1fns\n", actualMinCyclesT0H, actualMaxCyclesT0H, actualMinNanosecondsT0H, actualMaxNanosecondsT0H)
fmt.Fprintf(buf, " // T1H: %2d - %2d cycles or %.1fns - %.1fns\n", actualMinCyclesT1H, actualMaxCyclesT1H, actualMinNanosecondsT1H, actualMaxNanosecondsT1H)
fmt.Fprintf(buf, " // TLD: %2d - cycles or %.1fns -\n", actualMinCyclesTLD, actualMinNanosecondsTLD)
fmt.Fprintf(buf, " mask := interrupt.Disable()\n")
fmt.Fprintf(buf, " value := %s\n", archImpl.valueTemplate)
fmt.Fprintf(buf, " uint32_t value = %s;\n", archImpl.valueTemplate)
asm := archImpl.template
asm = strings.TrimSpace(asm)
asm = strings.ReplaceAll(asm, " @DELAY1\n", strings.Repeat(" nop\n", delay1))
asm = strings.ReplaceAll(asm, " @DELAY2\n", strings.Repeat(" nop\n", delay2))
asm = strings.ReplaceAll(asm, " @DELAY3\n", strings.Repeat(" nop\n", delay3))
asm = strings.ReplaceAll(asm, "\n", "\n\t")
fmt.Fprintf(buf, " device.AsmFull(`%s`, map[string]interface{}{", asm)
fmt.Fprintf(buf, " char i = 8;\n")
fmt.Fprintf(buf, " __asm__ __volatile__(\n")
for _, line := range strings.Split(asm, "\n") {
fmt.Fprintf(buf, "\t\t%#v\n", line+"\n")
}
// Note: [value] and [i] must be input+output operands because they modify
// the value.
fmt.Fprintf(buf, ` : [value]"+r"(value),
[i]"+r"(i)
: [maskSet]"r"(maskSet),
[portSet]"m"(*portSet),
[maskClear]"r"(maskClear),
[portClear]"m"(*portClear));
}
`)

// Now write the buffer contents (with the assembly function) to a file.
_, err := f.Write(buf.Bytes())
return err
}

func writeGoWrapper(f *os.File, arch string, megahertz int) error {
// Create the Go function in a buffer. Using a buffer here to be able to
// ignore I/O errors.
buf := &bytes.Buffer{}
fmt.Fprintf(buf, "\n")
fmt.Fprintf(buf, "func (d Device) writeByte%d(c byte) {\n", megahertz)
fmt.Fprintf(buf, " portSet, maskSet := d.Pin.PortMaskSet()\n")
fmt.Fprintf(buf, " portClear, maskClear := d.Pin.PortMaskClear()\n")
fmt.Fprintf(buf, "\n")
fmt.Fprintf(buf, " mask := interrupt.Disable()\n")
fmt.Fprintf(buf, " C.ws2812_writeByte%d(C.char(c), portSet, portClear, maskSet, maskClear)\n", megahertz)
buf.WriteString(`
"value": value,
"i": 8,
"maskSet": maskSet,
"portSet": portSet,
"maskClear": maskClear,
"portClear": portClear,
})
interrupt.Restore(mask)
}
`)
Expand Down Expand Up @@ -271,16 +292,26 @@ package ws2812
// Warning: autogenerated file. Instead of modifying this file, change
// gen-ws2812.go and run "go generate".

import (
"device"
"runtime/interrupt"
)
import "runtime/interrupt"

/*
#include <stdint.h>
`)
for _, megahertz := range clockFrequencies {
err := writeImplementation(f, *arch, megahertz)
err := writeCAssembly(f, *arch, megahertz)
if err != nil {
fmt.Fprintf(os.Stderr, "could not generate WS2812 assembly code for %s and %dMHz: %s\n", *arch, megahertz, err)
os.Exit(1)
}
}
f.WriteString(`*/
import "C"
`)
for _, megahertz := range clockFrequencies {
err := writeGoWrapper(f, *arch, megahertz)
if err != nil {
fmt.Fprintf(os.Stderr, "could not generate Go wrapper: %w\n", err)
os.Exit(1)
}
}
}
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